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Today in Weather History for April 1 April 1, 1912 A tornado with incredible velocity ripped into downtown Houston, TX, breaking the water table and giving the city its first natural waterspout. (The Weather Channel) April 1, 1923 Residents in the eastern U.S. awoke on "April Fool's Day" to bitterly cold temperatures. The mercury plunged to -34 degrees at Bergland MI and to 16 degrees in Georgia. (David Ludlum) April 1, 1987 Forty-five cities across the southeastern U.S. reported record low temperatures for the date. Lows of 37 degrees at Apalachicola FL, 34 degrees at Jacksonville FL, 30 degrees at Macon GA, and 22 degrees at Knoxville TN, were records for April. (The National Weather Summary) April 1, 1987 A tornado touched down briefly during a snow squall on the south shore of White Fish Bay (six miles northwest of Bay Mills WI). A mobile home was unroofed and insulation was sucked from its walls. (The Weather Channel) April 1, 1988 A powerful spring storm produced 34 inches of snow at Rye CO, 22 inches at Timpas OK, 19 inches at Sharon Springs KS, and up to 35 inches in New Mexico. Severe thunderstorms associated with the same storm spawned a tornado which caused 2.5 million dollars damage at East Mountain TX. (The National Weather Summary) (Storm Data) April 1, 1989 Up to six inches of snow blanketed the Adirondacks of eastern New York State and the Saint Lawrence Valley of Vermont. Up to a foot of snow blanketed the Colorado Rockies. (Storm Data) (The National Weather Summary) April 1, 1990 Thunderstorms produced severe weather in Texas, from southern Arkansas and northern Louisiana to southern Georgia, and from northern South Carolina to the Upper Ohio Valley during the day and evening. Thunderstorms spawned a tornado at Evergreen AL, and there were more than eighty reports of large hail and damaging winds. Thunderstorms produced baseball size hail north of Bastrop LA, and produced damaging winds which injured one person west of Meridian MS. (The National Weather Summary) (Storm Data) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 31 March 31, 1890 Saint Louis, MO, received 20 inches of snow in 24 hours. It was the worst snowstorm of record for the St Louis. (David Ludlum) March 31, 1954 The temperature at Rio Grande City, TX, hit 108 degrees, which for thirty years was a U.S. record for the month of March. (The Weather Channel) March 31, 1962 A tornado struck the town of Milton, FL, killing 17 persons and injuring 100 others. It was the worst tornado disaster in Florida history. (David Ludlum) March 31, 1973 An F-2 tornado with a path of 72 miles from Jonesboro (Clayton County) to Athens (Clarke County) killed 2 people. It lasted almost 2 hours and caused $113,000,000. It was the costliest natural disaster in Georgia history at that time. (NWS Atlanta) March 31, 1987 March went out like a lion in the northeastern U.S. A slow moving storm produced heavy snow in the Lower Great Lakes Region, and heavy rain in New England. Heavy rain and melting snow caused catastrophic flooding along rivers and streams in Maine and New Hampshire. Strong southerly winds ahead of the storm gusted to 62 mph at New York City, and reached 87 mph at Milton MA. (The National Weather Summary) (Storm Data) March 31, 1988 March went out like a lion in eastern Colorado. A winter-like storm produced 42 inches of snow at Lake Isabel, including 20 inches in six hours. Fort Collins reported 15 inches of snow in 24 hours. Winds gusted to 80 mph at Centerville UT. Albuquerque NM received 14 inches of snow. (The National Weather Summary) (Storm Data) March 31, 1989 Afternoon thunderstorms produced severe weather from North Carolina to Pennsylvania. Thunderstorm winds gusted to 76 mph at Cape Henry VA. While squalls blanketed northwest Pennsylvania with up to 9 inches of snow, thunderstorms in eastern Pennsylvania produced golf ball size hail at Avondale. (Storm Data) (The National Weather Summary) March 31, 1990 The month of March went out just as it came in, like a lamb. Marquette MI, which started the month with a record high of 52 degrees, equaled their record for the date with a reading of 62 degrees. (The National Weather Summary) March 31, 2010 Jacksonville, Florida's, record streak of days with high temperatures below 80 degrees comes to an end at 105 days. It was also Jacksonville's first 80 degree reading of the year. The previous latest first 80 degree day was on March 14, 1978. Data courtesy of WeatherForYou View the full article

Today in Weather History for March 30 March 30, 1823 A great Northeast storm with hurricane force winds raged from Pennsylvania to Maine. The storm was most severe over New Jersey with high tides, uprooted trees, and heavy snow inland. (David Ludlum) March 30, 1899 A storm which buried Ruby, CO, under 141 inches of snow came to an end. Ruby was an old abandoned mining town on the Elk Mountain Range in the Crested Butte area. (The Weather Channel) March 30, 1977 Hartford, CT, hit 87 degrees to establish a record for the month of March. (The Weather Channel) March 30, 1987 A storm spread heavy snow across the Ohio Valley and Lower Great Lakes Region. Cleveland OH received sixteen inches of snow in 24 hours, their second highest total of record. Winds gusting to 50 mph created 8 to 12 foot waves on Lake Huron. The storm also ushered unseasonably cold air into the south central and southeastern U.S., with nearly one hundred record lows reported in three days. (The National Weather Summary) (Storm Data) March 30, 1988 A winter-like storm developed in the Central Rockies. Snowfall totals in Utah ranged up to 15 inches at the Brian Head Ski Resort, and winds in Arizona gusted to 59 mph at Show Low. (The National Weather Summary) (Storm Data) March 30, 1989 Thunderstorms developing along and ahead of a slow moving cold front produced large hail and damaging winds at more than fifty locations across the southeast quarter of the nation, and spawned a tornado which injured eleven persons at Northhampton NC. (The National Weather Summary) (Storm Data) March 30, 1990 Low pressure produced heavy snow in central Maine and northern New Hampshire, with up to eight inches reported in Maine. A slow moving Pacific storm system produced 18 to 36 inches of snow in the southwestern mountains of Colorado in three days. Heavier snowfall totals included 31 inches at Wolf Creek Pass and 27 inches at the Monarch Ski Area. (The National Weather Summary) (Storm Data) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 29 March 29, 1886 Atlanta, GA, was drenched with a record 7.36 inches of rain in 24 hours. (The Weather Channel) March 29, 1920 Clear Spring, MD, received 31 inches of snow in 24 hours to establish a state record. (Sandra and TI Richard Sanders - 1987) March 29, 1921 The temperature in Washington D.C. dropped from 82 degrees to 26 degrees thus ending an early spring. (David Ludlum) March 29, 1935 A severe duststorm blanketed Amarillo, TX, for 84 hours. During one six hour period the visibility was near zero. (28th-31st) (The Weather Channel) March 29, 1945 Providence, RI, hit 90 degrees to establish a March record for the New England area. (The Weather Channel) March 29, 1987 Thunderstorms spawned tornadoes in Mississippi, and produced high winds and heavy rain in Louisiana. Thunderstorm winds gusted to 92 mph at Houma LA, and caused a million dollars damage in Terrebonne Parish. Avondale LA was deluged with 4.52 inches of rain. (The National Weather Summary) (Storm Data) March 29, 1988 Severe thunderstorms in the Lower Mississippi Valley spawned a tornado which injured two persons at Bunkie LA, and produced high winds which down a large tree onto a trailer at Bastrop LA claiming the life of one child and injuring another. (Storm Data) (The National Weather Summary) March 29, 1989 Thunderstorms produced torrential rains in northeastern Texas and southwestern Arkansas. Longview TX reported 14.16 inches of rain. More than eleven inches of rain at Henderson TX caused a dam to give way, and people left stranded in trees had to be rescued by boat. Total damage in northeastern Texas was estimated at 10 to 16 million dollars. (The National Weather Summary) (Storm Data) March 29, 1990 Thunderstorms developing ahead of a cold front produced severe weather in southeastern Texas and southern Louisiana. Thunderstorms spawned seven tornadoes, including one which injured seven persons at Gray LA. Thunderstorms also produced golf ball size hail and wind gusts to 70 mph at Port O'Conner TX, and produced up to six inches of rain in Beauregard Parish LA. (Storm Data) March 29, 1997 A brief F-1 tornado touchdown knocked trees down in Blue Ridge (Fannin County). A mobile home was picked up and dropped onto another mobile home. In addition, the second floor of a house was taken off. (NWS Atlanta) March 29, 2007 Eighteen year old Corey Williams is killed by a lightning bolt in Carbondale, IL, at the Community High School's first home track meet of the season. March 29, 2011 A record 766 inches of snowfall at Boreal Ski Resort and nearly 59 feet at Squaw Valley in California's Sierra Nevadas are just two areas where snowfall records have been broke. Data courtesy of WeatherForYou View the full article

Today in Weather History for March 28 March 28, 1917 Thane Creek, AK, reported a snow cover of 190 inches. (The Weather Channel) March 28, 1920 The worst tornado disaster of record occurred in Chicago IL as a tornado killed 28 persons and caused three million dollars damage. (David Ludlum) March 28, 1920 An outbreak of tornadoes occurred on this date. The worst tornadoes occurred in Troup County where one tornado, possibly an F-4, moved through the town of West Point flattening a four block area and killing 9 people. Another tornado, possibly an F-4 also, hit the southeast side of LaGrange destroying the industrial area of the city. Several factories and a cotton mill were destroyed along with 40 homes and over 100 people were killed. As the tornado moved through rural Troup County, it is estimated that an additional 100 people were killed bringing the death toll to well over 200. The number of those injured completely overwhelmed local medical facilities and assistance had to be summoned from other areas of the state, including Atlanta. (NWS Atlanta) March 28, 1984 A violent outbreak of tornadoes hit the Carolinas. Thunderstorms spawned 22 tornadoes during the late afternoon and evening hours which killed 57 persons and injured 1248 others. Nearly half the deaths occurred in mobile homes. A tornado from near Tatum SC to southern Cumberland County NC was 2.5 miles in width at times. (The Weather Channel) March 28, 1987 A blizzard raged from southern Nebraska to central Iowa. Snowfall totals ranged up to 17 inches at Blue Hill NE. Winds gusted to 68 mph at Carroll IA. High winds produced snow drifts twenty feet high in western Iowa, and produced wind chill readings as cold as 30 degrees below zero in Nebraska. The snowfall total of 9.4 inches at Omaha NE was a record for the date. (Storm Data) (The National Weather Summary) March 28, 1988 Severe thunderstorms in central Oklahoma produced hail up to four inches in diameter causing 35 million dollars in southern Oklahoma County. Baseball size hail and seven inches of rain caused another eighteen million dollars damage in Stephens County. (The National Weather Summary) (Storm Data) March 28, 1989 Unseasonably warm weather prevailed from the Southern and Central Plains to the Atlantic coast. Eighteen cities reported new record high temperatures for the date. The afternoon high of 81 degrees at Beckley WV was a record for March, and the high of 90 degrees in downtown Baltimore MD tied their March record. (The National Weather Summary) March 28, 1990 A storm system brought heavy snow to the west central and southern mountains of Wyoming, and high winds to the Wasatch Mountains of northern Utah. Snowfall totals in Wyoming ranged up to ten inches at the Snowy Ski Range Area, and the storm pushed the snowfall total for the month at Cheyenne above 37 inches, surpassing their previous record for March of 35 inches. (The National Weather Summary) (Storm Data) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 27 March 27, 1890 An outbreak of tornadoes occurred in the Ohio Valley. One of the tornadoes struck Louisville KY killing 78 persons and causing four million dollars damage. (David Ludlum) March 27, 1950 A three day snowstorm in the High Plains Region finally came to an end. The storm produced 34 inches of snow in 24 hours at Dumont, located in the Black Hills of South Dakota, and a total of 50 inches. (David Ludlum) March 27, 1984 The temperature at Brownsville, TX, soared to 106 degrees, and Cotulla, TX, reached 108 degrees, equaling the March record for the U.S. (The Weather Channel) March 27, 1987 The second blizzard in less than a week hit eastern Colorado and western Kansas. Snowfall totals ranged up to 24 inches at San Isabel CO. Winds gusted to 50 mph at Goodland KS. The high winds piled snow into massive drifts, closing roads for days and killing thousands of cattle. Snow drifts thirty feet high were reported in northwest Kansas. (The National Weather Summary) (Storm Data) March 27, 1988 Temperatures rose quickly, then dropped just as rapidly, in the central U.S. Eight cities reported record high temperatures for the date as readings soared into the 80's. In southeastern Colorado, the temperature at Lamar CO reached 91 degrees. Strong southerly winds gusted to 63 mph at Gage OK. Strong northwesterly winds, gusting to 61 mph at Goodland KS, then proceeded to usher much colder air into the area. (The National Weather Summary) (Storm Data) March 27, 1989 Afternoon and evening thunderstorms produced severe weather in the south central U.S. Two tornadoes were reported, and there were 77 other reports of large hail and damaging winds. Baseball size hail was reported at Willow OK and Bartlesville OK. Twenty-six cities in the central and eastern U.S. reported new record high temperatures for the date, including Yankton SD with a reading of 84 degrees. (The National Weather Summary) (Storm Data) March 27, 1990 Temperatures dipped into the teens and single numbers in the northeastern U.S. Scranton PA tied their record for the date with a morning low of 18 degrees. Temperatures warmed into the 60's and lower 70's in the Pacific Northwest. The afternoon high of 65 degrees at Astoria OR equaled their record for the date. (The National Weather Summary) March 27, 1994 An outbreak of tornadoes occurred that was eventually called the Palm Sunday Outbreak. A total of five F-4 tornadoes and eleven F-3 tornadoes were reported that resulted in the loss of life of 17 people with at least 166 people injured, 71 of those injuries occurred in Pickens County. (NWS Atlanta) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 26 March 26, 1913 The Ohio River Basin flood reached a peak. Ten inch rains over a wide area of the Ohio River Basin inundated cities in Ohio, drowning 467 persons, and causing 147 million dollars damage. The Miami River at Dayton reached a level eight feet higher than ever before. The flood, caused by warm weather and heavy rains, was the second mostly deadly of record for the nation. (David Ludlum) March 26, 1954 The temperature at Allaket, AK, plunged to 69 degrees below zero. (The Weather Channel) March 26, 1971 Parts of northern and central Georgia experienced their worst snow and ice storm since 1935. Two day power outages ruined two million eggs at poultry hatches. Two persons were killed when a tree landed on their car. (25th-26th) (The Weather Channel) March 26, 1987 A cold front crossing the Plateau Region produced high winds in Utah causing some property damage. Winds gusted to 51 mph at Salt Lake City. (The National Weather Summary) (Storm Data) March 26, 1988 Twenty cities in the southwestern U.S. reported new record high temperatures for the date. Afternoon highs of 73 degrees at Flagstaff AZ, 90 degrees at Sacramento CA, 95 degrees at Santa Maria CA, 95 degrees at Los Angeles CA, 99 degrees at Tucson AZ, and 100 degrees at Phoenix AZ set records for March. (The National Weather Summary) March 26, 1989 The Easter Bunny brought record warm temperatures to the central U.S. while such records were still welcome. A dozen cities reported record warm readings, including Dodge City KS with an afternoon high of 88 degrees. Strong southerly winds gusted to 51 mph at Dodge City, and reached 55 mph at Salina KS. (The National Weather Summary) (Storm Data) March 26, 1990 Fair weather prevailed across the nation for the second day in a row. Freezing temperatures were reported in the Middle Atlantic Coast Region in the wake of an early spring snowstorm. Afternoon highs were again in the 70's and 80's in the southeastern U.S., and for the ninth day in a row, temperatures in the southwestern U.S. reached the 90's. (The National Weather Summary) March 26, 1999 A deep cold core upper low moving slowly east across the Southern Appalachians (Habersham, Rabun and Stephens Counties) brought a round of light snow, accompanied by heavier bursts of sleet and hail as thunderstorms developed. Accumulations ranged between 1 and 3 inches. (NWS Atlanta) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 25 March 25, 1843 A second great snowstorm hit the northeastern U.S. The storm produced snow from Maine all the way to the Gulf of Mexico. Natchez MS received three inches of snow, and up to 15 inches buried eastern Tennessee. Coastal Maine received 204 inches of snow that winter. (David Ludlum) March 25, 1914 Society Hill, SC, was buried under 18 inches of snow, establishing a state record. (Sandra and TI Richard Sanders - 1987) March 25, 1934 A spring storm produced 21 inches of snow at Amarillo TX in 24 hours. However, much of the snow melted as it fell, and as a result, the snow cover was never any deeper than 4.5 inches. (David Ludlum) March 25, 1948 For the second time in less than a week airplanes were destroyed by a tornado at Tinker AFB in Oklahoma City OK. A March 20th tornado destroyed fifty planes at Tinker AFB causing more than ten million dollars damage, and the March 25th tornado destroyed another thirty-five planes causing six million dollars damage. The first tornado struck without warning, and caused more damage than any previous tornado in the state of Oklahoma. The second tornado was predicted by Fawbush and Miller of the United States Air Force, and their accurate tornado forecast ushered in the modern era of severe weather forecasting. (The Weather Channel) (Storm Data) (The National Severe Storms Forecast Center) March 25, 1975 The town of Sandberg reported a wind gust to 101 mph, a record for the state of California. (The Weather Channel) March 25, 1983 Despite having seasonally moved into Spring, Winter was still holding on in north Georgia. Two inches of snow fell at Blairsville this day, ranking number seven on the highest daily snowfall amounts for the month of March at Blairsville. (NWS Atlanta) March 25, 1987 Heavy rain left rivers and streams swollen in Kansas and Nebraska, causing considerable crop damage due to flooding of agricultural areas. The Saline River near Wilson Reservoir in central Kansas reached its highest level since 1951. March rainfall at Grand Island NE exceeded their previous record of 5.57 inches. (The National Weather Summary) (Storm Data) March 25, 1988 An early season heat wave prevailed in the southwestern U.S. The high of 93 degrees at Tucson, AZ, was a new record for March. Windy conditions prevailed across the central and eastern U.S. Winds gusted to 60 mph at Minneapolis MN, and reached 120 mph atop Rendezvous Peak WY. (The National Weather Summary) (Storm Data) March 25, 1989 A Pacific storm brought wet weather to much of the western third of the country, with heavy snow in some of the higher elevations. La Porte CA was drenched with 3.56 inches of rain in 24 hours. Up to 24 inches of snow blanketed the Sierra Nevada Range. (The National Weather Summary) (Storm Data) March 25, 1990 Temperatures dipped below zero in the Northern Rocky Mountain Region. Hardin MT was the cold spot in the nation with a morning low of 10 degrees below zero. Freezing drizzle was reported in the Southern Plains Region, with afternoon highs only in the 30s from the Southern High Plains to Missouri and Arkansas. (The National Weather Summary) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 24 March 24, 1912 Residents of Kansas City began to dig out from a storm produced 25 inches of snow in 24 hours. The snowfall total was nearly twice that of any other storm of modern record in Kansas City before or since that time. A record 40 inches of snow fell during the month of March that year, and the total for the winter season of 67 inches was also a record. By late February of that year Kansas City had received just six inches of snow. Olathe KS received 37 inches of snow in the snowstorm, establishing a single storm record for the state of Kansas. (23rd-24th) (The Kansas City Weather Almanac) (The Weather Channel) March 24, 1975 A thunderstorm formed as a part of a squall line and produced a tornado in Atlanta. This tornado was later called The Governor's Tornado. It moved northeast across the western and northern sections of the city and damaged the Governor's Mansion. Losses totaled at $56.5 million. (NWS Atlanta) March 24, 1987 A winter-like storm in the central U.S. produced blizzard conditions from South Dakota to western Kansas. Snowfall totals ranged up to 24 inches at Neligh NE, with 19 inches at Winner SD. Winds gusting to 60 mph created twelve foot snow drifts in Nebraska stranding thousands on the highways. (Storm Data) (The National Weather Summary) March 24, 1988 Thunderstorms developing along a cold front produced severe weather from Minnesota to northeastern Texas. The thunderstorms spawned ten tornadoes, including one which injured five persons near Raymondville MO. (The National Weather Summary) (Storm Data) March 24, 1989 Low pressure off the coast of Virginia brought heavy rain to the Middle Atlantic Coast States, and heavy snow to the Northern Appalachians. Cape Hatteras NC was soaked with 5.20 inches of rain in 24 hours, and snowfall totals in Vermont ranged up to 12 inches. Winds gusted to 52 mph at New York City. (Storm Data) (The National Weather Summary) March 24, 1990 The storm system which produced heavy snow in the Lower Missouri Valley the previous day, spread heavy snow across parts of the Upper Ohio Valley and the Middle Atlantic Coast Region. Snowfall totals of 2.2 inches at Philadelphia PA and 2.4 inches at Atlantic City NJ were records for the date. Up to six inches of snow blanketed southern Ohio. In the Middle Atlantic Coast Region, snow coated the blossoms of cherry trees which had bloomed in 80 degree weather the previous week. (Storm Data) (The National Weather Summary) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 23 March 23, 1913 A vicious tornado hit the city of Omaha, NE. The tornado struck during the late afternoon on Easter Sunday, and in just twelve minutes cut a swath of total destruction five miles long and two blocks wide across the city killing 94 persons and causing 3.5 million dollars property damage. (David Ludlum) March 23, 1916 Pocatello, ID, received a record 14.6 inches of snow in 24 hours. (The Weather Channel) March 23, 1987 A blizzard raged across western Kansas, and the panhandle of Texas and Oklahoma. Pampa TX received 21 inches of snow, and winds gusted to 78 mph at Dodge City KS Altus OK. Governor Hayden declared forty-six counties in western Kansas a disaster area. In southwest Kansas, the storm was described as the worst in thirty years. (The National Weather Summary) (Storm Data) March 23, 1988 Thunderstorms developing along a strong cold front spawned tornadoes near Roberts ID and Bridger MT. Strong and gusty winds prevailed in the western U.S. Wind gusts in the southwest part of Reno NV reached 89 mph. (The National Weather Summary) (Storm Data) March 23, 1989 Charlotte and Wilmington, NC, reported rainfall records for the date as showers and thunderstorms prevailed in the southeastern U.S. Freezing rain glazed parts of North Carolina and southern Virginia. Gale force winds produced a heavy surf along the coast of North Carolina. (The National Weather Summary) (Storm Data) March 23, 1990 An upper level storm system produced heavy snow in the Lower Missouri Valley. Snowfall totals ranged up to nine inches at Kansas City MO, with eight inches reported at Falls City NE, Columbia MO and Saint Louis MO. Thunderstorms produced heavy snow in the Kansas City area during the evening rush hour. (The National Weather Summary) (Storm Data) March 23, 2007 A trailer is thrown through a bowling alley as a tornado moves through Clovis, NM. About 100 homes and businesses are destroyed, at least three schools are damaged and telephone poles are snapped. Thirteen tornadoes struck a dozen communities along the New Mexico/Texas border. Two people were critically injured. March 23, 2011 A series of tornadoes are spawned from severe thunderstorms in Pennsylvania. In Hempfield Township dozens of homes and a high school auditorium where students are rehearsing a play are severely damaged. Data courtesy of WeatherForYou View the full article

Today in Weather History for March 22 March 22, 1920 A spectacular display of the Northern Lights was visible as far south as Bradenton FL, El Paso TX, and Fresno CA. At Detroit MI, the display was described so brilliant as to blot out all stars below first magnitude. (22nd-23rd) (The Weather Channel) March 22, 1936 A great flood crested on rivers from Ohio to Maine. The flood claimed 107 lives and caused 270 million dollars property damage. (David Ludlum) March 22, 1954 Six to ten inch rains caused the Chicago River to overflow its banks. (The Weather Channel) March 22, 1987 An intense storm produced heavy snow in the southern and central Rockies, and high winds from southern California to West Texas. Wolf Creek Pass CO received 24 inches of snow, and winds gusted to 69 mph at Ruidoso NM. Blizzard conditions were reported in eastern Colorado. (The National Weather Summary) (Storm Data) March 22, 1988 Rain and high winds battered the Northern Pacific Coast Region, with wind gusts to 78 mph at Ocean Shores WA. The high winds uprooted trees and down power lines. Ten cities in the northeastern U.S. reported new record low temperatures for the date. Eight cities in the central U.S. reported record highs. Southerly winds gusting to 60 mph helped push the mercury at Ottumwa IA to a record warm reading of 83 degrees. (Storm Data) (The National Weather Summary) March 22, 1989 Six cities in the Great Lakes Region, and three in southern Texas, reported new record low temperatures for the date, including Alpena MI with a reading of 9 above zero, and Brownsville TX with a reading of 38 degrees. (The National Weather Summary) March 22, 1990 A surge of arctic air kept temperatures in the teens and 20's during the day in the north central U.S., and heavy snow fell over parts of Montana. Record warmth was reported in the western U.S.,and in Alaska. Phoenix AZ reported a record high of 94 degrees, and the town of Barrow, located along the arctic coast of Alaska, reported a record high of 20 degrees. (The National Weather Summary) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 21 March 21, 1932 A tornado swarm occurred in the Deep South. Between late afternoon and early the next morning severe thunderstorms spawned 31 tornadoes in Alabama, Mississippi, Georgia and Tennessee. The tornadoes killed 334 persons and injured 1784 others. Northern Alabama was hardest hit. Tornadoes in Alabama killed 286 persons and caused five million dollars damage. (David Ludlum) March 21, 1952 Severe thunderstorms spawned thirty-one tornadoes across Arkansas, Tennessee, Missouri, Mississippi, Alabama and Kentucky. The tornadoes killed 343 persons and caused 15 million dollars damage. Arkansas and Tennessee each reported thirteen tornadoes. The towns of Judsonia AR and Henderson TN were nearly wiped off the map in what proved to be the worst tornado outbreak of record for Arkansas. A tornado, one and a half miles wide at times, left a church the only undamaged building at Judsonia. (David Ludlum) (The Weather Channel) March 21, 1987 A winter storm in the Northern High Plains Region produced blizzard conditions in western South Dakota. Winds gusted to 70 mph at Rapid City SD, and snowfall totals ranged up to 20 inches at Lead SD. The high winds produced snow drifts six feet high. (The National Weather Summary) (Storm Data) March 21, 1988 Bitterly cold weather prevailed across the northeastern U.S. Portland ME reported their coldest spring day of record with a morning low of 5 above, and an afternoon high of just 21 degrees. Marquette MI reported a record low of 15 degrees below zero. (The National Weather Summary) (The Weather Channel) March 21, 1989 Snow blanketed the northeastern U.S. early in the day, with six inches reported at Rutland VT. Morning and afternoon thunderstorms produced large hail and damaging winds from southwestern Mississippi to southwest Georgia. (The National Weather Summary) (Storm Data) March 21, 1990 The first full day of spring was a cold one for the eastern U.S. Freezing temperatures damaged 62 percent of the peach crop in upstate South Carolina, and 72 percent of the peach crop in the ridge area of South Carolina. Elkins WV, which a week earlier reported a record high of 82 degrees, was the cold spot in the nation with a morning low of 16 degrees. (Storm Data) (The National Weather Summary) March 21, 2006 Rain and thunderstorms from later on the previous day, caused flooding in Fulton and Jones Counties. In Fulton County, Big Creek near Alpharetta rose to 8.2 feet, 1.2 feet above flood stage. The flooding affected Alpharetta Greenway and about 200 feet of the Greenway had to be closed. In Jones County, the river gage on Falling Creek rose to 15.3 feet, 2.3 feet above flood stage. In both cases, damage was confined to minor debris cleanup. (NWS Atlanta) Data courtesy of WeatherForYou View the full article

Today in Weather History for March 20 March 20, 1875 a massive tornado outbreak tore through the Southeast, with Georgia the hardest hit. Several of the tornadoes were of F-4 strength and overall took a total of 96 lives. (NWS Atlanta) March 20, 1924 A late winter storm in Oklahoma produced nearly a foot of snow at Oklahoma City and at Tulsa. (David Ludlum) March 20, 1948 The city of Juneau received 31 inches of snow in 24 hours, a record for the Alaska capitol. (20th-21st) (David Ludlum) March 20, 1984 A severe three day winter storm came to an end over the Central Plains. The storm produced up to twenty inches of snow in Colorado, Nebraska and Kansas, and left a thick coat of ice from eastern Kansas across northwestern Missouri into Iowa. (Storm Data) March 20, 1987 A storm produced blizzard conditions in Wyoming and eastern Nebraska, and severe thunderstorms in central Nebraska. Snowfall totals ranged up to 12 inches at Glenrock WY and Chadron NE. Thunderstorms in central Nebraska produced wind gusts to 69 mph at Valentine, and wind gusts to 76 mph at Bartley. (Storm Data) (The National Weather Summary) March 20, 1988 Squalls in the Great Lakes Region left up to eight inches of new snow on the ground in time for the official start of spring. Unseasonably warm weather prevailed in the western U.S. Seven cities reported new record high temperatures for the date, including Tucson AZ with a reading of 89 degrees. (Storm Data) (The National Weather Summary) March 20, 1989 Snow and high winds created blizzard conditions in western Kansas to usher in the official start of the spring season. Thunderstorms produced severe weather from east Texas to Alabama and northwest Florida, with nearly fifty reports of large hail and damaging winds during the afternoon and evening hours. (The National Weather Summary) (Storm Data) March 20, 1990 The northeastern U.S. was in the midst of a snowstorm as spring officially began at 4 19 PM. Snowfall totals in the Green Mountains of Vermont ranged up to thirty inches, and up to 15 inches of snow was reported in the Catskills and Adirondacks of eastern New York State. Totals in eastern Pennsylvania ranged up to 12 inches at Armenia Mountain. The storm resulted in one death, and forty-nine injuries. (The National Weather Summary) (Storm Data) March 20, 1996 Snow fell in northern Georgia on the first day of spring. Amounts of up to five inches fell in the northeast Georgia mountains. Up to one inch fell on grassy areas as far south as Atlanta. Numerous traffic accidents were reported, including a 15 car pile-up in the northern suburbs of Atlanta that killed one person. (NWS Atlanta) March 20, 2005 An F1 tornado hits South San Francisco. Trees are uprooted. At least twenty homes and twenty businesses are damaged, including the city's new fire station. March 20, 2006 Grand Island, NE, receives 17.8 inches of snow in 24 hours, breaking the old local record for the most snowfall in a day by 4.8 inches. 29.7 inches in 48 hours also breaks a record. Data courtesy of WeatherForYou View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article

The main focus on this article is not to make a winter forecast, but to explore what effects El Nino's and teleconnections have on winter weather across the southeast. One of the main sources of data in this report comes from a weather friend of mine that I call "Brother Larry". Larry would prefer to remain anonymous, so from here on out you'll hear me refer to Larry as "Brother Larry". :-) Larry has a wealth of information about the weather history in Georgia, and I'll be using a lot of his findings to help give you an idea how this winter may turn out, based on the environment created by the El Nino, as well as several other factors. Again, this data is based on analog years, or those years that most closely identify with the current patterns, so keep that in mind. Analog's are not perfect, but they do give us a very good idea about how things have happened in the past and how they may happen again in the future. Again, almost all of the text below (other than a few of my own edits and additions) is from Larry, and he gets all the credit for the research and stats. ​ ENSO and Southeast US Winters This data was compiled by taking a list of 26 “cold” US winters (Dec/Jan/Feb) since 1894 -1895 (i.e., the coldest 23%) for the eastern third of the US. This requires solid, widespread, below normal anomalies, and requires the southeast to be pretty chilly itself. The two maps to the right were created with data from the list of years below, but that dataset only goes back to 1948, so the maps I'm displaying are not 100% complete with the years in the list. Here's the list of those winters, and you can see the years I used on the maps themselves. Also, Larry's 26 coldest winters study was done the better part of 10 years back, since then, it is possible that some of 09, 10, 13, 14, etc. could be added, although he is not reassessing those now. 2002 - 20031995 - 19961993 - 19941981 - 19821980 - 19811978 - 19791977 - 19781976 - 19771969 - 19701968 - 19691967 - 19681963 - 19641962 - 19631960 - 19611947 - 19481939 - 19401935 - 19361917 - 19181911 - 19121909 - 19101904 - 19051903 - 19041901 - 19021900 - 19011898 - 18991894 - 1895 Temperature Anomalies Precipitation Nino Base State ENSO Regions ONI Chart from Golden Gate Weather Services - http://ggweather.com/enso/oni.png Forecast So now that we have our list of base years, let's look at the base Nino state for those winters. Before we can do that, we need to take a look at the various Nino/Nina classifications. Graphs and Charts The Oceanic Niño Index (ONI) has become the standard that NOAA uses for identifying El Niño (warm) and La Niña (cool) events in the tropical Pacific. The ONI is defined as the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 50N-50S, 120W-170W). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5 anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into: Weak (with a 0.5 to 0.9 SST anomaly)Moderate (1.0 to 1.4)Strong (1.5 to 1.9)Very Strong (≥ 2.0) For the purpose of this blog post, for an event to be categorized as weak, moderate, strong or very strong, it must have equaled or exceeded the threshold for at least 3 consecutive overlapping 3-month periods. Here's an analysis of the 26 cold winters by ENSO state: Strong Nino: 0 of 26 (0%)Moderate Nino: 1 of 26 (4%)Weak Nino: 9 of 26 (35%)Neutral positive: 4 of 26 (15%)Neutral negative: 5 of 26 (19%)Weak Nina: 6 of 26 (23%)Moderate Nina: 1 of 26 (4%)Strong Nina: 0 of 26 (0%) Dec-Feb temperature anomalies during weak Nino's Notice that out of all the cold years, the majority of them occurred during weak Nino's (35%). Also notice that out of all of those cold winters, none of them occurred with a strong Nino or a strong Nina. The map on the left depicts the temperature anomalies that occurred during a Weak Nino. Due to the data only going back to 1948, all of the years are not depicted, but this will give you a good idea. As you can see, a weak Nino is what we'd like to see come Dec-Feb. If the current one stays too strong, it could severely limit our cold this winter based on past analogs. keep in mind, Larry's study is based on temperatures, not precipitation. ​ ​Nino and the Pacific Decadal Oscillation (PDO) +PDO or Warm State -PDO or Cold State PDO Index (http://www.daculaweather.com/4_pdo_index.php) While it's easy to look at one specific weather pattern, there are many factors that determine how a winter will turn out, with the ENSO state being just one of those. But there are other teleconnections and long term patterns that also have an effect on our winter weather, and they all work in tandem with each other. Graphs and Charts Now we are going to turn our attention to the PDO state or Pacific Decadal Oscillation. First, the definition from the National Center for Environmental Information: "The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999). " Here's an analysis of the cold 26 winters by DJF averaged PDO status:+ PDO: 18 of 58 (31%)- PDO: 8 of 57 (14%)Again, much as it was with weak Nino's, many of our coldest winters occurred during a + PDO state, while only 8 out of 57 occurred during a negative PDO state. ​ Nino and the North Atlantic Oscillation (NAO) In order for us to get long lasting cold air that stays locked in, we need some blocking. There are several teleconnection patterns that aid in developing this blocking, one of which is the North Atlantic Oscillation or NAO. Graphs and Charts Negative NAO (-NAO) Positive NAO (+NAO) Here's the definition of the NAO: "The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the Arctic Oscillation, and varies over time with no particular periodicity." Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe. Opposite patterns of temperature and precipitation anomalies are typically observed during strong negative phases of the NAO. For us, negative is what we're looking for in the winter. Let's take a look at the analysis of the cold 26 Dec-Feb winters by averaged NAO status: – NAO: 19 of 48 (40%)+ NAO: 7 of 67 (10%)Again, a large number of the cold winters had a negative NAO. ​​ Piecing It All Together... Now let's take the combination of the ENSO state (in our case, Nino), and factor in the PDO and NAO and let's see what we get. Here's the analysis of the 26 cold winters by a combination of Dec-Feb averaged PDO and NAO status:+ PDO/-NAO: 12 of 25 (46%)- PDO/-NAO: 7 of 23 (30%) (all 7 had (PDO – NAO) > 0)+ PDO/+NAO: 6 of 33 (18%)- PDO/+NAO: 1 of 34 (3%)Things start to change a little. Obviously, the combination of +PDO and -NAO are the best combination, and that makes perfect sense. During the positive phase of the PDO, the wintertime Aleutian low is deepened and shifted southward, warm/humid air is advected along the North American west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the southeastern United States. Add the effects of the blocking provided by the NAO and you lock in the cold air instead of having it rush out to sea. Now, let's really lay it out. Here's "Brother Larry's" analysis of the 26 cold winters by a combination of ENSO state and Dec-Feb averaged PDO and NAO status: Strong Nino:+PDO/-NAO: 0 of 6 (0%)-PDO/-NAO: 0 of 1 (0%)+PDO/+NAO: 0 of 7 (0%)-PDO/+NAO: 0 of 1 (0%) Moderate Nino:+PDO/-NAO: 1 of 2 (50%)-PDO/-NAO: 0 of 0 (N/A)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 2 (0%) Weak Nino:+PDO/-NAO: 6 of 7 (86%)-PDO/-NAO: 2 of 2 (100%)+PDO/+NAO: 1 of 2 (50%)-PDO/+NAO: 0 of 4 (0%) Neutral Positive:+PDO/-NAO: 2 of 4 (50%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Neutral Negative:+PDO/-NAO: 1 of 3 (33%)-PDO/-NAO: 2 of 7 (29%)+PDO/+NAO: 2 of 10 (20%)-PDO/+NAO: 0 of 5 (0%) Weak Nina:+PDO/-NAO: 2 of 2 (100%)-PDO/-NAO: 3 of 5 (60%)+PDO/+NAO: 1 of 4 (25%)-PDO/+NAO: 0 of 7 (0%) Moderate Nina:+PDO/-NAO: 0 of 1 (0%)-PDO/-NAO: 0 of 3 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 1 of 4 (25%) Strong Nina:+PDO/-NAO: 0 of 0 (N/A)-PDO/-NAO: 0 of 2 (0%)+PDO/+NAO: 0 of 0 (N/A)-PDO/+NAO: 0 of 6 (0%) Conclusions... Weak Nino’s give the highest percentage chance for cold of any of the ENSO states by far (with weak Nina’s second); however, a combo of -PDO/+NAO seems to make it difficult even for weak Nino’s.A very impressive 13 of 16 (81%) of the aggregate of weak Nino's and weak Nina's with -NAO were cold.Don't ever bet on cold with either a strong Nino or a strong Nina since none of the 23 were cold.+PDO about doubles the percent chance for cold versus a -PDO.A -NAO more than doubles the percentage chance for cold versus a +NAO and a somewhat higher chance than a +PDO gives. So, I give small edge to –NAO over a +PDO regarding cold prospects. Regardless, both are very important.A +PDO/-NAO combo gives close to twice the percentage chance for cold versus the percentage chance for all PDO/NAO combos in the aggregate.A -PDO/-NAO is the next best combo for cold prospects, but mainly if NAO is more negative than PDO.Don't ever bet on cold with a combination of -PDO/+NAO, since only 1 out of 34 were cold.If there is a +PDO, the chances for a –NAO appear to be high for only weak to moderate Nino’s. The chances appear to only be about 50-50 for strong Nino’s. For neutral ENSO, the chances seem to be surprisingly low (partial negative correlation suggested).The best shot at a +PDO/-NAO combo appears to be with a weak to moderate Nino's. On the other hand, only 3 of 34 (9%) Nina’s had a +PDO/-NAO.A pretty high 17 of 34 (50%) Nina’s had a –PDO/+NAO.A +PDO is difficult with a moderate to strong Nina. Only one out of 16 (6%) had one.A –PDO seems rather difficult with a strong Nino, only 2 out of 15 (13%) had one.+PDO and –PDO winters are about evenly split. But +NAO winters have been a bit more common than -NAO in long term: 58% vs. 42%. Winter Precipitation Regarding wintry precipitation for Atlanta, when looking at the three standalone super Nino's (1972-1973, 1982 -1983, 1997-1998) as well as the six strong to super strong 2nd year Nino's (1877-1888, 1888-1889, 1896-1887, 1905-1906, 1940-1941, 1987-1988), Atlanta more often than not, had one major winter storm, but not always:1877-1888: 2.5" 1/3/1878 & a non-major freezing rain followed on 1/9/18781888-1889: 6" 2/21/18891896-1967: 6.2" 12/2/18961905-1906: 6.2" for the season including 3.5"+ major 1/26/1906, measurable snow D, J, and F1940 -1941: only T of snow1972 -1973: historic ZR 1/7-8/1973, which included 1" mainly ice pellets; (also, historic snow hit central GA in Feb though Atlanta missed that one)1982 -1983: 10.3" S/IP for season including 7.9" 3/24/1983 (heaviest since 1940) and measurable snow J, F, and M1987- 1988: 4.2" of mainly IP 1/7/1988 (would have been ~8" if all snow)1997- 1998: only 0.6" 12/29/1997 View the full article