Thursday, October 19

[NorthGeorgiaWX]

Good morning!

We're headed toward the end of the month, with another 5-6 days of relatively cool temperatures in store for our area before we warm up slightly. 

Clouds and moisture will be on the increase today, as another trough and an area of low pressure heads our direction. By this afternoon, we should be mostly cloudy, and during the day tomorrow we may see a few showers and thunderstorms. We're not going to see much rain out of this system, so don't expect help in relieving the dry conditions that are in place across the state. The new drought maps will be out this morning, so we'll see how much worse things have gotten over the last week.

Once the front passes, gusty winds will bring another round of below normal temperatures to north Georgia, although it won't be as cold as the October 8th cold front, and you may not even notice the change other than the air will be drier. One reason we won't get as cool, is that we may see a surge of moisture in the upper levels from Hurricane Norma, bringing cloudy conditions for Sunday. Unfortunately, the mid and lower levels of the atmosphere won't get the same moisture levels, so rain is probably not in the cards that day. 

 

Next week is another transition week, as we warm up slightly, and stay that way for 7 days or so, but the start of November will bring another shot of cooler weather. As we move into the month before winter, we need to keep looking ahead and what might be coming down the road. 

 

While there are multiple things we need to look at over the winter months, one important teleconnection holds the key to getting colder weather across the eastern US, and that is the PNA, or Pacific-North American Oscillation. 

The positive phase of the PNA pattern features above-average barometric pressure heights in the vicinity of Hawaii and over the inter-mountain region of North America, and below-average heights located south of the Aleutian Islands and over the southeastern United States. The PNA pattern is associated with strong fluctuations in the strength and location of the East Asian jet stream. The positive phase is associated with an enhanced East Asian jet stream and with an eastward shift in the jet exit region toward the western United States. The negative phase is associated with a westward retraction of that jet stream toward eastern Asia, blocking activity over the high latitudes of the North pacific, and a strong split-flow configuration over the central North Pacific.

The positive phase of the PNA pattern is associated with above-average temperatures over western Canada and the extreme western United States, and below-average temperatures across the south-central and southeastern US. 

As you can see, a positive PNA is what we want to see if we want winter across the eastern US. As we enter the month of November, we see the PNA rise to a positive state. When the PNA goes positive, it basically cuts off the flow of warm moist Pacific air into the lower 48 states, instead forcing that air up and over the top toward higher latitudes. 

 

Looking at the Euro Extended, we see another positive rise around the middle of the month, and again toward the end of the month. The PNA is a good indicator of the placement of western US ridging. With a ridge to the west, and trough will be to the east over us. 

 

I think our next step down in temperatures will come about a week or so into November. I wanted to see how that first real cold front (October 8th) changed our temperatures, so I went back did a little analysis.

I looked at three periods, 5 days, 10, days, and 20 days, before and after the front, to compare temperatures. The first 5 day period saw a 6.2 degree drop in the highs, the 7 day period after the front, averaged 8.3 below the pervious 7, and at 10 days, was 10.5 below the 10 day period before the front. That was a pretty nice step down.

 

Be careful with the data you use to judge the strength of the El Nino, as this isn't a typical El Nino. There are several reasons why our winter won't turn out like a "typical" (if there is such a thing) El Nino. Here is the "typical" El Nino map from NOAA. This is NOT what is going to happen this year.

 

 

The last Super El Nino we had was in 2016, and you can see how it compares to the current El Nino. We are WAY below where that Nino was at this point in time. The MEI incorporates both ocean AND atmospheric parameters and gives a more comprehensive look at the ENSO state. When comparing the typical El Nino strength to the MEI, we start to see that the atmosphere is not coupled with the water temperatures, and therefore not responding in a typical fashion. 

 

There is not much difference in the typical El Nino regions to the oceanic base state, and we are currently in a La Nina base state.

I went back to look at some of my old data, that looked at the 26 coldest winters here in Georgia. This study is relatively old (the last year was 2003), so it doesn't include some of the more recent years, but these are the winters it does cover. 
 

• 2002 - 2003
• 1995 - 1996
• 1993 - 1994
• 1981 - 1982
• 1980 - 1981
• 1978 - 1979
• 1977 - 1978
• 1976 - 1977
• 1969 - 1970
• 1968 - 1969
• 1967 - 1968
• 1963 - 1964
• 1962 - 1963
• 1960 - 1961
• 1947 - 1948
• 1939 - 1940
• 1935 - 1936
• 1917 - 1918
• 1911 - 1912
• 1909 - 1910
• 1904 - 1905
• 1903 - 1904
• 1901 - 1902
• 1900 - 1901
• 1898 - 1899
• 1894 - 1895

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 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%)

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. 

I won't get into all of the data here, and if you'd like to read it, this is the link that will take you there. 

 

Here are the general conclusions.

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%.

 

So there are some things to consider as we head toward winter. Let's see how the cards fall!

 

We may see a sprinkle or two a little later, as a very weak line of showers and light rain move in from Alabama, I don't think that we'll much if anything from this except for clouds. 

 

And in case you are wondering what the global average temperature is right now... 🙂 

 

Have a great day!

[happyatsea]

Thank you for fixing this page so I can read it now!! Love the great information!!

[RickyD]

Steve

We lived in a messed up world, so forgive my question.  Why are some of the Mets still saying we will have a record strong El Nino? 
My own thoughts ARE not good thoughts about this, but maybe I have not heard the facts correctly?? 
 

.06 now vs 2.5 etc etc etc. That is what i have heard about strength. 

[NorthGeorgiaWX]

5 minutes ago, RickyD said:

Steve

We lived in a messed up world, so forgive my question.  Why are some of the Mets still saying we will have a record strong El Nino? 
My own thoughts ARE not good thoughts about this, but maybe I have not heard the facts correctly?? 
 

.06 now vs 2.5 etc etc etc. That is what i have heard about strength. 

Because they aren't looking at the entire picture. They are looking at this number, the ONI.

They are leaving out the atmospheric side of things (MEI). If the atmosphere doesn't react in tandem with the sea temps, then the "normal" result El Nino won't occur, and that is what is happening. Most meteorologist say that the atmosphere isn't "coupled", and not responding like it would during a strong El Nino. 

The thought is that since the oceans are warmer than they use to be, the warmer El Nino water has less of an impact than it use to.  Also keep in mind, the warmer water is migrating west toward the central Pacific, and that changes things as well. 

 

[NorthGeorgiaWX]

 

 

[NorthGeorgiaWX]

Time to begin smiling...

 

[RickyD]

Ray from Raysweather of Boone has gone modern, 😊 and updated his website. You now have to be a paid subscriber, to enjoy his services. 
He put out his winter weather forecast today.  He is expecting somewhat under 2010 level of snow amounts it looks for the Appalachians.