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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
152 AM EST Thu Dec 19 2019

Valid 12Z Sun Dec 22 2019 - 12Z Thu Dec 26 2019

  • Heavy rain over parts of the Southeast exiting Monday

Overview:

Upper troughing off the West Coast will be reinforced from the
northwest and slowly move onshore next week, maintaining an
unsettled pattern. Concurrently, a potent southern stream system
will track across Florida late this weekend and then push slowly
out to sea. Locally heavy rain will be possible around its
circulation between northern Florida and coastal North Carolina.

Guidance/Predictability Assessment:

Across the West, the general troughing pattern seems well-resolved
in the longwave pattern, but there remained timing differences
through about Tuesday and then both feature and timing differences
thereafter. A consensus position was favored, somewhat near the
12Z ECMWF/Canadian until next Wed/Thu when they may become too
deep/slow (near the slowest 10% of ensembles) but not unreasonable
given the pattern. The GFS/GEFS may be too quick overall by later
in the period which can be their bias.

In the Southeast, models were still struggling with the forward
speed and track of the closed low and surface low but forecast
convergence continues. The GFS continues to be on the quicker side
while the 12Z UKMET lagged the more centered 12Z ECMWF/Canadian,
which were close to the ensemble consensus and was the preferred
solution. Did not rule out the quicker GFS given the
quasi-progressive nature of the pattern--western trough would not
allow too much of a slower solution though it could trend slower
in tandem.
Multi-day ensemble trend has mostly stabilized so will
continue to favor the best-clustered models.


Weather Highlights/Threats:

Western troughing will support fairly widespread but light to
modest precipitation next week, spreading inland as height lower
to the east. There remains considerable uncertainty as to how much
precipitation moves into the Plains around Christmas Day into the
26th, owing to how much Gulf moisture may be tapped. For now,
favored the slower/drier ECMWF/Canadian ensembles vs the
quicker/wetter GEFS.
Temperatures will trend cooler in the West
behind the front next week.

The Gulf system will provide at least modest rainfall for much of
the Southeast with locally heavy amounts continuing out of the
short range Saturday. Several additional inches of rain is quite
possible Sun-Mon with sufficient moisture in the lower atmosphere
and good inflow off the Atlantic. Some light snow is possible on
its northern fringe in the marginally colder air of the southern
Appalachians, but the event is expected to be nearly all rain.

Warmer than average temperatures are forecast to spread from the
Northern Rockies and Plains eastward across much of the rest of
the U.S., with high temperatures up to 20 degrees above average.
Dry conditions should persist across much of the Mississippi
Valley to Ohio Valley and Mid-Atlantic/Northeast.


Fracasso

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
137 AM EST Fri Dec 20 2019

Valid 12Z Mon Dec 23 2019 - 12Z Fri Dec 27 2019

  • Heavy rain and gusty winds possible along parts of the Southeast U.S. coast on Monday

Overview and Guidance/Predictability Assessment:

Model/ensemble show a persistent upper-level mean trough generally
across the West Coast and Great Basin through the medium range.

Meanwhile, moderately progressive flow will persist downstream
across the central and eastern U.S as shortwave energy ejects from
the western trough and encounters broad anticyclonic flow across
the south central and southeastern states.
A persistent
upper-level low across the Arctic Ocean well north of Alaska along
with weakly positive height anomalies across Canada will keep the
risk of any significant outbreaks of cold air across the CONUS to
a minimum during the medium range.

A relatively deep upper low and associated low pressure system are
forecast to begin pulling away from the Southeast Mon-Tue (days
3-4), and models/ensemble members have shown a convergence toward
the middle of the spread in terms of timing over the past couple
cycles, with the ECMWF/GFS safely in the middle of the spread.

Farther west, modest timing/amplitude differences were evident in
the guidance with a shortwave reaching California Mon night/Tue,
and then de-amplifying across the central/eastern U.S. Wed-Thu
(days 5-6)
as a relatively weak/multi-centered surface frontal
wave moves from the central U.S. to the Ohio Valley. Models show
general agreement that another shortwave should approach the West
coast late Wed, although some differences and run-to-run
variability remain as to the precise timing as well as the
structure (closed-off upper low or a more open wave). The 12Z
ECMWF and the past couple runs of the GFS have trended toward a
more open wave. Finally, a similar thing can be said about another
trough forecast by the ECMWF/GFS to reach the West Coast on Fri
(day 7) as the previous shortwave reaches the Plains.

A blend of the 12Z ECMWF/18Z GFS was heavily used in the WPC
forecast for days 3-5, with a shift to gradually heavier weight
placed on ensemble means during days 6-7. Overall, forecast
confidence through the period was average to slightly above
average.


Weather Highlights/Threats:

Models show some degree of consensus that a band of moderate to
heavy rains is possible on Mon on the north side of the low
pressure system slowly pulling away from the Southeast U.S.
coastline.
The model consensus suggests 1-3 inches of rain are
possible on Mon along portions of the coast before the system
pulls out to sea by Tue. This system may also produce areas of
strong winds due to a rather intense pressure gradient north of
the surface low.
Farther west, scattered rain/mountain snow
showers will be possible across the Four Corners region Mon-Tue as
a shortwave passes overhead, with rain (and potentially wintry
precipitation on the northern fringe) from the Central Plains late
Tue into the Midwest on Wed. Increasing moisture return across the
Southern Plains by late Thu ahead of the next shortwave could
produce areas of rain in an overrunning-type setup north of a
frontal boundary. Rain and mountain snow is expected to become
much more widespread along the West Coast, California in
particular, by the mid to latter portion of next week as the last
of the described upper troughs reaches the coast.

Temperatures are forecast to be above average across much of the
central and eastern U.S. during the medium range.
The largest
temperature anomalies are forecast from the Central Plains to the
Midwest Mon-Tue, where high temperatures may approach or exceed 20
deg F above average. A broad area of the central/eastern U.S. will
see highs 5 to 15 deg above average into at least the latter
portion of next week.
Meanwhile, with persistent upper-level
troughing, much of the West will see temperatures near or slightly
below average.

Ryan

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
135 AM EST Sat Dec 21 2019

Valid 12Z Tue Dec 24 2019 - 12Z Sat Dec 28 2019

Overview and Guidance/Predictability Assessment:

Models/ensembles show a persistent upper-level mean trough
generally across the West Coast and Great Basin through the medium
range. Meanwhile, moderately progressive flow will persist
downstream across the central and eastern U.S. as shortwave energy
ejects from the western trough and encounters broad anticyclonic
flow across the south central and southeastern states
. A
persistent upper-level low across the Arctic Ocean well north of
Alaska along with weakly positive height anomalies across Canada
will keep the risk of any significant outbreaks of cold air across
the CONUS to a minimum during the forecast period.

A relatively deep upper-level low and associated low pressure
system are forecast to begin be pulling away from the Southeast on
Tue (day 3). Over the past 24 hours, models have converged a bit
toward the slower side of the spread. With the ECMWF remaining
slower than the GFS, leaned somewhat toward the slower ECMWF
solution.
Farther west, model timing/amplitude differences
continued to be evident in the guidance with a shortwave reaching
California early Tue, and then deamplifying across the
central/eastern U.S. Wed-Thu (days 4-5) as a relatively weak
frontal wave moves from the central U.S. to the Ohio Valley.
Models show general agreement that another trough or potentially a
closed upper low should approach the West Coast either late Wed or
early Thu. Fairly significant differences remain, however. The
ECMWF has trended toward a much deeper/closed and slowly
progressing system, while the GFS has remained a more open wave,
albeit trending slower/deeper with each consecutive run, and the
00Z GFS at least hinting at the potential for a closed upper low
around the time the feature nears the coast. Given the trends,
preferred to lean more toward the ECMWF since it seemed to be
leading the way on the current trends. During the day 6-7
(Fri-Sat) time period, additional northern stream shortwave energy
appears likely to move across the CONUS northern tier, with
deterministic solutions showing a range of timing/amplitude for
these features, favoring heavier use of ensembles means.

Based on the described considerations, the WPC forecast was
initially based on a blend of the 12Z ECMWF/18Z GFS during days
3-4, with quite a bit more emphasis placed on the ECMWF. For days
5-7, a blend of the ECMWF along with the the ECENS/GEFS ensemble
means was used.


Weather Highlights/Threats:

Scattered rain/mountain snow showers are expected across the Four
Corners region Tue as a shortwave passes overhead. Increasing
moisture return across the Southern Plains starting Thu night and
continuing through late in the week may produce areas of rain in
an overrunning-type setup north of a frontal boundary. Some wintry
weather may be possible on the northern fringe of this area of
precipitation, from portions of the Central Plains to the Midwest,
although precipitation amounts in those areas look rather light at
this point in time. Rain and mountain snow are expected to become
much more widespread along the West Coast by Wed-Thu, continuing
through late in the week for the Northwest, as the last of the
described troughs and additional smaller scale northern stream
energy move onshore.

Temperatures are forecast to be above average across much of the
central and eastern U.S. The largest temperature anomalies are
forecast from the Central Plains to the Midwest/Ohio Valley
Tue-Wed, where high temperatures of 15 to 20 deg F above average
will be common. A broad area of the central/eastern U.S. will see
highs 5 to 15 deg above average persisting through the end of next
week. Meanwhile, with persistent upper-level troughing, much of
the West will see temperatures near or slightly below average.

Ryan

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
126 AM EST Mon Dec 23 2019

Valid 12Z Thu Dec 26 2019 - 12Z Mon Dec 30 2019

Overview and Guidance/Predictability Assessment:

An amplified flow pattern is expected across the CONUS during the
medium range forecast period, with a progressive northern stream
and a less progressive southern stream with a slow-moving
upper-level low. A consolidated vortex across the Arctic Ocean and
an active Pacific wave pattern will keep any significant arctic
air outbreaks away from the CONUS, with many locations, especially
across the central and eastern U.S. experiencing unusually mild
conditions for late December.

A shortwave and associated frontal system are forecast to cross
the Midwest/Great Lakes/Northeast Thu-Fri night. Models were
relatively agreeable here, with differences primarily confined to
the strength of the shortwave and the depth of the surface low as
it moves into east central Canada. Farther west, an upper-level
low is forecast to be initially near or just off the southern
California coast early on Thu (day 3). Models have struggled to
resolve the timing of this system as it moves east across the
Southwest and eventually into the central U.S., and guidance is
not much closer to a resolution than this time last night. The
ECMWF continues to be on the slow side of the spread, but with a
substantial degree of support from a seemingly underdisbursed
ECENS. Meanwhile, the GFS remains on the fast side of the spread
(albeit at least a bit faster than the GEFS ensemble mean). These
described differences worsened through time during the forecast
period, ultimately resulting in cascading spread downstream by the
weekend as the system approaches/reaches the central U.S., and
potentially interacts with progressive northern stream waves. The
preference in this forecast was to lean at least a bit more toward
the faster timing, using blend of roughly 1/3 each of the 12Z
ECMWF/UKMET and 18Z GFS for days 3-4, with increased weight placed
on ECENS/NAEFS ensemble means by day 5 due to quickly increasing
guidance spread. This solution still supports the idea of low
pressure developing along a front across the Southern Plains Fri
night/Sat, quickly moving northeast into the Great Lakes by Sun
morning, and the cold front sweeping off the Eastern Seaboard on
Mon. Forecast confidence with this system by Sun-Mon remained
rather low.

Models show general agreement that another trough and potential
upper-level low should dig along the West Coast by Sun-Mon (days
6-7). Run-to-run differences among guidance were significant
enough with this feature to go heavily toward ECENS/NAEFS ensemble
means by that time period.


Weather Highlights/Threats:

Rain and mountain snow are expected Thu across the Southwest as
the upper low moves onshore. Progressive upper-level flow will
keep rain/mountain snow a possibility across the Olympics and the
Cascades late this week. Moisture return ahead of the southern
stream system will create an overrunning setup north of a frontal
boundary across the Southern/Central Plains Thu-Fri, with
relatively widespread (and at least locally heavy) rain expected
to develop. By next weekend, with potential development of a low
pressure system across the central U.S., models indicate the
potential for a band of moderate to possibly heavy precipitation
from the Southern Plains to the Ohio Valley/Great Lakes, although
details remain elusive for reasons described above. Nonetheless,
there appears at least some potential for an area of winter
weather on the north side of this system (despite the relative
lack of significant cold air). Once models get a better handle on
the specifics of next weekend's system, a clearer picture will
emerge as to what degree of heavy rain and/or winter weather
threat exists. At this time, the greatest probabilities associated
with this potential low pressure system are indicated across
portions of the southern Rockies and southern High Plains Fri/Fri
night. See the medium range Winter Weather Outlook products for
more details on the winter weather threat.

Temperatures are forecast to be well above average across much of
the eastern half of the CONUS through late this week. The largest
temperature anomalies are forecast from the Mid-Mississippi Valley
to the lower Great Lakes and Ohio Valley on Thu, where high
temperatures may approach or exceed 20 deg F above average in some
areas. A broad area will see highs 5 to 15 deg above average
through Saturday before the arrival of cooler temperatures behind
the cold front. Meanwhile, with persistent upper-level troughing
in place much of the Great Basin and Southwest will see high
temperatures 5 to 10 deg below average into the weekend.

Ryan

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
145 AM EST Tue Dec 24 2019

Valid 12Z Fri Dec 27 2019 - 12Z Tue Dec 31 2019

Overview and Guidance/Predictability Assessment:

A mid/upper-level shortwave and the associated frontal system are
forecast to cross the Northeast on Fri (day 3). Model consensus
was good with this system and no major differences were noted. The
most significant forecast issue during the medium range continues
to be the progression/evolution of an upper-level low initially
across the northern Baja Peninsula early Fri, which is then
forecast to move east across the Southwest and toward the central
U.S. by Sat. After several days of strikingly different solutions
among the guidance with respect to the forward progression of the
system, and resultant differences in interaction/phasing with
northern stream energy across the central U.S., some trends have
finally emerged that may shed some light on the eventual outcome.
The ECMWF along with a number of ECENS members have increased the
forward speed of the system, although not to the point of the GFS
yet. The ECMWF (along with the UKMET/CMC to some degree) are still
slow enough with their progression that the system misses its
chance for any significant interaction with the northern stream
wave, and continues to progress more slowly eastward across the
lower Mississippi Valley/Southeast as a cutoff upper low. The GFS,
on the other hand, has remained steadfast in its idea of the
southern stream wave reaching the Southern Plains by Fri night,
where it begins an interaction with a northern stream shortwave,
resulting in the development of a relatively deep low pressure
system across the Plains and Midwest Sat-Sun (days 4-5). This
system bears quite a few similarities to a similar system several
weeks ago for which the GFS significantly outperformed much of the
other guidance in the medium range, the origin of which (for both)
seems to be a shortwave initially over the data sparse North
Pacific, south of the Aleutians. Given these factors, opted to
lean heavily toward the GFS (18Z run) during days 3-5, along with
a gradually increasing component of the ECENS/GEFS ensemble means
as well (both of which provided a significant degree of support to
an idea similar to the GFS). Following this idea, the phased
system should cross the Northeast late Sun/Mon, with the cold
front moving off the Eastern Seaboard by Monday morning.

Models continue to show an additional trough/upper low digging
southward along the West Coast Sun-Mon, with most deterministic
solutions showing another cutoff low near/across southern
California by Mon. Deterministic solutions are quite similar with
the timing and evolution of this feature, although a look at
ensemble members shows that spread is perhaps a bit higher than
would be indicated by deterministic guidance alone. Given some
general consensus among the guidance, a gradual trend toward
heavier use of ECENS/GEFS ensemble means continued through days
6-7 (Mon-Tue).


Weather Highlights/Threats:

The upper low crossing the Southeast on Fri is expected to
mountain snow to portions of the Southwest and southern Rockies.
Ahead of the upper low, an overrunning setup across the
Southern/Central Plains is expected to result in development of an
area of precipitation, which should expand northward and eastward
across the Plains and eventually the Midwest/Mississippi Valley
through time as the eventual low pressure system spins up. Locally
heavy rain will be possible for some areas, while in the northern
portion of this precipitation shield, sufficient cold air may
exist for precipitation to fall as a wintry mix/and or snow. The
winter weather potential appears to be focused in a band from the
southern Rockies to the central High Plains on Fri, extending into
the Midwest/Upper Great Lakes by Sat. Given at least somewhat
improved confidence in this scenario, boosted winter weather
outlook probabilities across the Midwest/Great Lakes Sat/Sat
night. Please see the medium range winter weather outlook products
for more details on the winter weather threat. As the system
continues east, winter weather is possible across portions of the
Northeast Sun/Sun night in the cool air mass north of the warm
front, with rains expected farther south along the cold front
across the Appalachians, Mid-Atlantic, and Southeast.

Temperatures are forecast to be well above average across the
central and eastern U.S. Fri-Sun ahead of the eventual low
pressure system. High temperatures of 10 to 20 deg F above average
are forecast across a large area. The cold front forecast to
arrive over the weekend will bring an end to the warm temperatures
from west to east, with temperatures returning to near seasonal
norms.
Meanwhile, given persistent lower heights across the
interior western U.S., highs are forecast to be 5 to 10 deg below
average from the Great Basin to much of the Southwest Fri-Sun,
with temperatures moderating somewhat by early next week.

Ryan

Ryan

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
129 AM EST Thu Dec 26 2019

Valid 12Z Sun Dec 29 2019 - 12Z Thu Jan 02 2020

  • Significant winter storm expected to impact portions of the Upper Midwest and Upper Great Lakes this weekend

Overview and Guidance/Predictability Assessment:

A relatively deep upper-level and surface low are forecast to be
in place across the Midwest Sunday morning (day 3), with a
potential winter weather event for portions of the Upper
Midwest/Great Lakes expected to be ongoing. Model consensus for
this system has improved substantially over the past couple days,
and all deterministic solutions show the deep surface low moving
relatively slowly into the upper Great Lakes by Mon morning and
into Ontario by Tue morning. This is a trend toward a slower
progression of this feature shown by some of the ECMWF yesterday.
Farther east, a triple point low is expected to develop somewhere
across the Northeast on Mon, although models differ on the exact
timing of this feature, but agree that it should remain relatively
weak and progressive. Overall the GFS has outperformed the ECMWF
during the medium range with this system, however, so was
reluctant to lean too heavily on the ECMWF and opted to go with a
GFS/ECMWF blend.

Farther west, a similar scenario as seen in at least a couple
instances recently looks to occur again, with nearly all guidance
forecast a shortwave to separate from an active North Pacific jet
and dive southward along the U.S. West Coast as it amplifies, with
development of a closed upper low expected on Mon.
Most guidance
shows the system continuing a slow drift southeastward through Tue
before eventually coming under the influence of an amplifying
trough farther north, and moving east more quickly. The ECMWF
continues to be a bit less amplified initially, and slower to
close the feature off than the majority of other guidance (and is
even a bit less amplified with the wave on Mon than the ECENS
ensemble mean - a bit of a red flag for the deterministic
solution
). 12Z/18Z guidance showed some consensus that a surface
low could develop across the Southern Plains by Wed night/Thu as
the merged upper trough moves east. The 00Z GFS made a significant
change by days 6-7 (Wed-Thu), and is now much slower to move the
trough/upper low eastward across the Southwest/northern Mexico and
merge it with the northern stream trough, which would keep a phased
southern stream low from developing in the manner shown by
previous guidance. Overall, models are fairly inconsistent by that
time frame, so a more ensemble based blend seemed in order.

The WPC forecast was initially based on a blend of the 18Z GFS/12Z
ECMWF during days 3-5, with a shift to majority ECENS/GEFS
ensemble mean weighting during days 6-7.


Weather Highlights/Threats:

As low pressure develops and begins to deepen moves northeastward
across the Midwest/Great Lakes Sun-Mon, an area of precipitation
is expected to accompany the system. Potentially significant
accumulating snows are expected Sun-Sun night across portions of
the Upper Midwest/Great Lakes. Accumulating winter weather will
also be possible for northern New England Sun/Sun night, likely
continuing into part of Mon before changing to rain. Please see
the medium range winter weather outlook products for more details
on the winter weather threat. Farther south along the cold front,
rain is expected across the Southeast, Appalachians, and
Mid-Atlantic regions through Sun night before the cold front moves
offshore on Mon.
Across the Pacific Northwest, as the shortwave
moves onshore early next week, rain and mountain snow are forecast
to develop across the coastal ranges and Cascades in Oregon and
Washington, potentially spreading farther inland into portions of
the northern Rockies by midweek. As the next cutoff southern
stream system begins to interact with a northern stream trough and
approaches the central U.S. by next Tue-Wed, ample moisture from
the Gulf of Mexico is forecast to be pulled northward into the
system, with the potential for widespread showers and
thunderstorms across portions of the western/central Gulf Coast
and lower Mississippi Valley, with the potential for areas of
heavy rain.
Confidence in this aspect of the forecast is a bit
below average at this time,
however, given model variability with
the forward speed of the cutoff upper low.

Temperatures are forecast to be well above average across the
central and eastern U.S. on Sun ahead of the low pressure system.
High temperatures of 15 to 25 deg F above average are forecast
across portions of the Ohio Valley, central Appalachians, and
Great Lakes, with a much of the eastern third of the country at
least 10 deg F above average ahead of the cold front.
Low
temperatures across these area on Sunday are forecast to be 20 to
35 deg F above average, with a number of record high minimum
temperatures likely. These warm conditions should moderate
somewhat by Mon as they shift to the Mid-Atlantic/Northeast. The
cold front forecast to arrive by Sun-Mon will bring an end to the
warm temperatures from west to east, with temperatures returning
to near seasonal norms.
Meanwhile, given persistent lower heights
across the interior western U.S., highs are forecast to be 5 to 10
deg below average from the Great Basin to much of the Southwest
and portions of the Great Basin and central/southern Rockies
through much of the forecast period.

Ryan

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
145 AM EST Fri Dec 27 2019

Valid 12Z Mon Dec 30 2019 - 12Z Fri Jan 03 2020

  • Significant winter storm expected to impact parts of the Upper Great Lakes into Upper Great Lakes/Northeast early next week
  • Heavy rainfall potential from the western-central Gulf Coast region northeastward mid-late next week


Overview and Guidance/Predictability Assessment:

The guidance continues to show fairly good agreement at least with
respect to the large scale mean flow. The upper low over the Upper
Midwest early day 3/Monday will track gradually northeast while
another vigorous upper system drops southward along or just inland
from the West Coast. As the West Coast feature reaches over or
near northwest Mexico, strong North Pacific flow should reach into
western North America. Models show upper ridging over the east
Pacific to strengthen by the middle of next week, which eventually
should lead to amplified troughing over the central U.S./northern
Mexico by next Thursday and Friday.

Though large scale flow evolution shows good agreement through the
period, there remains some fairly notable differences with respect
to timing of the various systems. For the initial Midwest upper
low, some timing differences remain, but there seems to be a trend
towards the slower ECMWF/CMC. This would allow for more high
pressure to build into eastern Canada for a time, leading to a bit
slower northward progress of triple point wave development
tracking from off the northern Mid-Atlantic coast into the
Canadian Maritimes by Wednesday.

Meanwhile, fairly significant differences continue for the energy
dropping southward along the West Coast.
The GFS/GEFS mean remain
slower than the ECMWF/ECENS mean but have trended slightly faster
with the past couple of runs. The latest CMC runs are slower than
the ECMWF, but still faster than the GFS, while the latest UKMET
sits right in between the ECMWF and CMC. This difference has
significant influence downstream involving how quickly moisture
spreads from near the Gulf Coast and northeastward Tuesday night
onward with the GFS scenario the slowest.

There remains some differences in the evolution of reinforced
amplified troughing across the Central U.S. at the end of the
period with respect to the North American energy dropping into the
West. The CMC is much faster to push this trough eastward next
Friday/day 7 than the remainder of the guidance and the means
(even its own).

Based on the above evaluation, the WPC blend for days 3-5 used a
majority deterministic guidance blend between the 12z
ECMWF/CMC/UKMET with smaller contributions from the 18z GEFS/12z
ECENS means. After day 5, increased the weighting of the ensemble
means and removed the CMC from the blend (and the UKMET since it
is not available past 12z day 5). Was able to incorporate some of
the 18z GFS past day 5 though as it became more similar to the
ECMWF and the ensemble means with the larger scale pattern. This
blend resulted in good continuity from the previous WPC shift.


Weather Highlights/Threats:
By the start of the medium range period (Monday), the storm system
initially over the Upper Great Lakes should weaken in favor of a
developing coastal wave off the Northeast coast. Precipitation
with this system will be ongoing across the Upper Lakes into the
Northeast Monday into Tuesday with snow likely across northern
areas. The latest WPC medium range winter weather outlook shows
the best chance for accumulating significant snowfall across far
northeast Minnesota/northern Wisconsin, as well as across interior
New England.

Precipitation (lower elevation rain and mountain snows) across the
Pacific Northwest will be ongoing through much of the period as
subsequent waves of energy move onshore. Some moisture should
reach into the Intermountain West, though with lesser intensity.

Ahead of the upper low in northern Mexico, ample moisture from the
Gulf of Mexico is likely to surge northward across the eastern
half of the country by the middle to later part of next week.
Expect a period of widespread showers and thunderstorms across
portions of the western/central Gulf Coast and lower Mississippi
Valley, which should eventually spread northeastward into the
Tennessee Valley/central Appalachians as well. While confidence
remains low for precise timing and duration, the models continue
to show a decent signal for a meaningful rainfall event over this
general area.

The warm sector ahead of the initial Upper Great Lakes storm will
contain much above normal temperatures to start next week, with
some readings as much as 20F above normal over the Mid-Atlantic.
Frontal passage will bring a cooling trend but only to
near/moderately above normal levels.
Central U.S. trough
amplification aloft late in the period should encourage a warmer
trend again over the East by next Thu. Areas from the
central/southern Rockies into the Southwest are likely to see the
most persistent below average temperatures with some areas
averaging 5-10F below normal for highs through the Mon-Fri period.

Santorelli

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
156 AM EST Sat Dec 28 2019

Valid 12Z Tue Dec 31 2019 - 12Z Sat Jan 04 2020

  • Significant winter storm expected to continue Tue across northern New England
  • Heavy rainfall potential over the Lower Mississippi Valley next Thursday


Overview:

A lead upper low will move along the US/Canadian border Tue/Wed
which will spread a swath of snow through northern New York and
New England. In the West, a deep upper low will swing through Baja
California and old Mexico Wed-Fri before eventually lifting
northeastward. This may support a heavy rainfall potential from
eastern Texas into Louisiana/Arkansas and perhaps farther east
late in the week. In the Pacific Northwest, a couple frontal
passages will bring in modest precipitation to the region.


Guidance/Predictability Assessment:

Models and ensembles showed good clustering on the first couple
days of the forecast, and a deterministic blend of the 12Z/18Z GFS
and 12Z ECMWF/Canadian/UKMET served as a good starting point. The
quicker GFS runs in the east were offset by a slower progression
in the West/Southwest/Mexico compared to the ECMWF/Canadian/UKMET.
By about next Thursday, the largest differences among the guidance
were over Texas/Mexico with the upper low.
The 18Z/12Z GFS were
slower than the UKMET which was slower than the Canadian. The 12Z
ECMWF was quickest of the deterministic models and even among the
quickest 1/5th or so of ensemble members (and quicker than its
previous two runs). Given the strength of the system over Mexico,
was reluctant to believe the quickest solution was plausible. The
ensemble means were just a bit quicker than the GFS and somewhat
like the Canadian, and formed the starting point for that feature
next Thu-Sat as it lifts northeastward. Building ridging over
Florida (500mb height anomalies over +2 sigma near Cuba) should
favor a slower solution as well.

Back to the West, 12Z GFS was not preferred as the ensembles
showed increased troughing into the West with a cold front
progressing eastward and southward. 18Z GFS was a bit lower with
heights but still higher than the ensemble means. The 12Z ECMWF
was more aggressive with height falls so an intermediate solutions
was preferred given the uncertainty leading up to next Sat.


Weather Highlights/Threats:

Exiting surface low off New England (and trailing parent low over
the Great Lakes) will leave a trail of snow for parts of northern
NY and much of NH/VT into Maine. Temperatures will trend upwards
after the storm departs as heights rise from the west. Focus will
then be on the Pacific Northwest with and incoming front on
Tuesday pushing through the northern Rockies Wednesday and onto
the Plains by early Thursday, where it may be rather
moisture-starved. Highest precipitation will be over coastal areas
and the Cascades with additional snow along the Divide. To the
south, upper low will lift out of Mexico toward the Lower MS
Valley. Cold front will link up with the Gulf warm front on the
tail-end of the departing New England front which may help tap
Gulf moisture and bring in an area modest to locally heavy
rainfall by Thursday. After that, it remains unclear how resilient
this system may be but at least some rainfall will spread eastward
through the Southeast on Friday.
By then, another front will
likely enter the Pacific Northwest which will bring in another
round of lowland rain and mountain snows, along with cooler
temperatures behind it.

Fracasso

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1256 AM EST Mon Dec 30 2019

Valid 12Z Thu Jan 02 2020 - 12Z Mon Jan 06 2020

  • Heavy rainfall potential over the Lower Mississippi Valley to the Southern Appalachians Thu-Fri

Overview and Guidance/Predictability Assessment:

Broad troughing will settle over the central and eastern states by
next week after a reversal of the pattern at the beginning of the
period this Thursday. The models and ensembles were in good
agreement to start the forecast but drifted apart by the weekend
and especially by next Monday. The 12Z ECMWF and Canadian offered
reasonable clustering with the 18Z GEFS mean and 12Z ECMWF
ensemble mean to use as a starting point, with added details from
the 12Z UKMET and 12Z/18Z GFS to start.

Areas of contention were first with the weakening upper low
(likely just a sharp trough by 12Z Thu) over Mexico, lifting to
the northeast. With three separate streams crossing 100W, the
models have wavered on how each interacts (or doesn't) with each
other aloft, and consequently at the surface. The 12Z/18Z GFS
were likely too quick with the Mexican trough but perhaps too slow
with the trailing shortwave out of the Rockies, and it was not
preferred past Thursday. Lead and trailing surface systems will
attempt to merge together by the time they reach New England
around late next Fri into Sat.

Next area of contention lied in the west, with a large amount of
uncertainty in the upstream central North Pacific flow. This has
led to large timing differences in how quickly or slowly to lower
heights in the West starting Sat and then progress eastward and
southward next Sun/Mon. Again there, the ECMWF/Canadian paired
closer to the ensemble means as the GFSs were nearly completely
out of phase. By next Mon, no deterministic model really fit the
lead-in pattern suggested by the means, though the degree of
spread couldn't rule out any model either. Favored the ensemble
means in whole at the expense of any detail.


Weather Highlights/Threats:

As the weakening upper low or sharp trough lifts out of Mexico,
moisture from the Gulf will get drawn across the surface warm
front along the coast which will lead to an expanding area of
rainfall and some embedded convection. This may be accentuated via
additional weak surface wave development along the front. Heaviest
rainfall may occur from Louisiana across Mississippi into Alabama,
especially Thu. The system is expected to weaken Fri, but some
rainfall is expected over areas farther northeast over portions of
the Tennessee Valley to Southern Appalachians.
Nearly daily bouts
of precipitation are likely for the Northwest into the Northern
Rockies during the period, focused over coastal areas and the
Coastal Range/Cascades in addition to the Idaho
Panhandle/northwestern Montana. Temperatures will generally be
near to above average east of the Rockies through the weekend and
near to below average in the West. By next week, more of the
country may see below average temperatures than above as troughing
becomes established.


Fracasso

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
153 AM EST Tue Dec 31 2019

Valid 12Z Fri Jan 03 2020 - 12Z Tue Jan 07 2020

  • Heavy rainfall threat continues across the Southeast on Friday

Overview/Guidance Assessment:

Upper troughing shifting from the Central to Eastern U.S. Fri-Sun
will induce a heavy rainfall threat ahead of it in the Southeast.

The guidance shows pretty good agreement Friday/Day 3 with broad
troughing across the Great Plains. After this, the GFS (and the
UKMET) has been pretty consistent with wanting to close off an
upper low over the Midwest, and race the shortwave eastward
through the weekend. The ECMWF/CMC are a bit slower with the upper
trough, not quite as developed, and that seems to fit better with
the ensemble means.

A couple of shortwaves enter the Pacific Northwest on Saturday and
again on Sunday, the latter of which guidance shows good agreement
will amplify as it crosses the Rockies on Monday, ejecting into
the Plains on Tuesday. The latest runs of the GFS/ECMWF have the
ECMWF a bit slower/more amplified than the GFS, but run-to-run
continuity has been fairly poor with the details. Yet another
shortwave trough looks to approach southwest Canada on Tuesday/Day
7, though the deterministic solutions show quite a bit of
variability with the evolution of this feature. Preferred a blend
more towards the agreeable ensemble means (GEFS/ECENS mean) by the
end of the period.


Weather Highlights/Threats:

Gulf of Mexico moisture will get drawn ahead of the trough lifting
through the mid-south continuing a threat for heavy rainfall from
the end of the short range period into parts of the
Southeast/southern Appalachians.
Surface low across the Ohio
Valley deepens, and reforms off the Northeast coast by Saturday,
and depending on development of the upper system, could bring a
period of snow north and west of the low from the Upper Midwest to
northern/interior New England. Nearly daily bouts of precipitation
are likely for the Northwest into the Northern Rockies during the
period, focusing more over coastal locations and the Coastal
Range/Cascades. Above to well above normal temperatures across the
eastern third of the country Friday and Saturday should moderate
to near normal following passage of the cold front
, with above
normal temperatures also moving across the Western U.S. in the
Central states this weekend.

Santorelli

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Can’t find the discussion, but that January 8 system looked good for NGA and the Carolinas!☃️

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Starting today, I will also be including the short range discussion in addition to the extended discussion.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Wed Jan 1 2020

Valid 12Z Wed Jan 1 2020 - 12Z Fri Jan 3 2020

  • Heavy rain returns to the Gulf Coast and heavy snow for the northern Rockies

Heavy rain and thunderstorms will be making a return to portions of the
Deep South and into the Tennessee River Valley to begin 2020.  There will
be a deep surge of moisture from the western Gulf of Mexico ahead of a
longwave trough over Mexico and a warm front lifting northward across the
Gulf Coast region.  Current indications suggest 2 to 4 inches of rainfall
from Louisiana to southern Tennessee, and there may be some instances of
flooding with a Slight Risk of excessive rainfall from WPC in effect for
parts of these areas.
 A few strong to severe thunderstorms can also be
expected.

For the Pacific Northwest, a pair of cold fronts will make their way
inland with a surge of moisture off the Pacific.  The result will be heavy
rain for coastal areas of Washington and Oregon, and heavy snow for the
Olympics and Cascades.  The central and northern Rockies will also be
affected by these storm systems with at least a foot of snow possible for
the higher elevations of northern Idaho and western Montana through
Thursday morning.

Elsewhere across the continental U.S., lake effect snow is expected
downwind of Lake Erie and Lake Ontario as cold northwesterly winds cross
the warmer waters.  Mainly dry conditions are expected across the Florida
Peninsula, the Desert Southwest, and the central Plains.  Much of the
central and eastern U.S. should begin the new year with temperatures near
to above normal, and near to below normal for the Rockies and parts of the
Intermountain West.

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-------------------------------------------------

 

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
158 AM EST Wed Jan 01 2020

Valid 12Z Sat Jan 04 2020 - 12Z Wed Jan 08 2020


Overview/Guidance Assessment:

The pattern across the CONUS during the medium range period
(Sat-Wed) looks to be progressive with an active stream of
shortwave troughs traversing the country. An amplified upper
trough initially in place across the Ohio/Tennessee Valleys on
Saturday will move off the East Coast by Sunday, resulting in a
deepening low pressure system across the Great Lakes and
Northeast. Minor timing differences with this trough (or closed
low), with the GFS/CMC a hair faster than the ECMWF/UKMET days 3
and 4 and the ensemble means in the middle.

To the West, a series of systems moving onshore and tracking
eastward through time continues to show increasing spread in the
guidance, especially toward the end of the forecast period. The
first shortwave enters the West coast day 4, with another
following quickly on day 5. It's with this second one where models
continue to struggle with evolution as it ejects eastward out of
the Rockies and into the Central U.S. day 5 and beyond.
The ECMWF
has been quite consistent in showing a much more amplified trough
especially days 6 and 7, which would bring a rapidly deepening
surface low from the south-central Plains on Day 5, into the
Northeast on day 7.
The CMC shows a similar evolution, with the
GFS quite a bit flatter/weaker. There is not a ton of ensemble
support yet for that strong of a low as depicted by the ECMWF, but
given the good run-to-run consistency from the ECMWF, and the
pattern set-up, it is not completely unreasonable. Prefer a blend
of the ensemble means at this point, with small contributions from
the ECMWF for some added definition from the means. A third
shortwave moves into the West on day 7, but there is high spread
with timing and strength of this low, that the ensemble means were
heavily favored.


Weather Highlights/Threats:

Surface low moving through the Northeast on day 3, will bring
precipitation from the Lower Great Lakes into New England,
possibly in the form of snow. Nearly daily bouts of precipitation
are likely for the Northwest into the Northern Rockies during the
period, focusing more over coastal locations and the Coastal
Range/Cascades. Deepening on evolution of the trough/surface low
development across the Central U.S. day 5-7, some snow may be
possible north and west of the low across parts of the Ohio Valley
to the Northeast end of the period. ECMWF and CMC show a much
better chance for this, though confidence is low at this time.

Above normal temperatures across the Northeast on Saturday should
moderate to near normal following passage of the cold front. Above
normal temps shift across the Great Plains towards the Midwest
days 3-5, with much of the country near normal by days 6 and 7.

Santorelli

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
206 AM EST Thu Jan 2 2020

Valid 12Z Thu Jan 2 2020 - 12Z Sat Jan 4 2020

  • Heavy rain returns to the South and another storm system for the Northwest

Widespread moderate to heavy rain and thunderstorms have made a return to
the Gulf Coast region as a moisture rich disturbance lifts northward from
the Gulf of Mexico.
 This feature will be ahead of a longwave trough over
Mexico and the High Plains, and a warm front lifting northward across the
Gulf Coast region will provide additional instability for some strong to
severe thunderstorms.  The Storm Prediction Center has a Slight Risk of
severe thunderstorms across portions of Louisiana and Mississippi for
Thursday.  In terms of heavy rainfall, current indications suggest the
potential for 3 to 5 inches of rainfall from central Mississippi to
eastern Tennessee, and there will likely be some instances of flash
flooding where there are multiple rounds of thunderstorm activity.  Flood
watches are in effect for these areas.

For the Pacific Northwest, heavy rain can be expected for coastal areas of
Washington and Oregon, and heavy snow for the Olympics and Cascades.  By
Friday night, a strong cold front approaches the region with a powerful
surface low crossing British Columbia.  The result will be strong winds
and high surf for the coastal areas, and additional heavy precipitation
can be expected for the Pacific Northwest and northern Rockies as this
front moves inland Saturday morning.

Elsewhere across the continental U.S., mainly dry conditions are expected
across the Desert Southwest and extending eastward to the central Plains. 
Much of the central and eastern U.S. will have temperatures that feel more
like March instead of January ahead of the cold front,
and near to below
normal for the Rockies and parts of the Intermountain West.

D. Hamrick

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--------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1035 AM EST Thu Jan 02 2020

Valid 12Z Sun Jan 05 2020 - 12Z Thu Jan 09 2020


Overview/Guidance Assessment:

A progressive westerly flow pattern is on tap for next week for
the CONUS
. Uncertainty regarding track and intensity of embedded
shortwaves remains the main concern with the greatest uncertainty

with a trough/low potentially developing over the Great Lakes
region and shifting northeast from there in the middle of next week

The initial deep cyclone pivoting into a negatively tilted trough
exits the Northeast coast Sunday. The 00Z CMC remains too quick
with the system and the GFS is now the farthest west/closest to
the New England coast. However, clustering is decent with the
ECMWF/UKMET/GFS, so a preference is for the 00Z ECMWF/UKMET with
some GFS.

The progression of the shortwave initially over the northern Great
Plains Sunday looks to play a key role in subsequent development
east from there toward the midweek as remnants may interact with
the next trough that quickly shifts inland across the western
CONUS Sunday. The GFS shears less of this trough, allowing a
closed mid-level low to develop over/just north of the Great Lakes
Monday. A similar pattern is seen in the UKMET, just displaced a
bit north. The presence of this low disrupts development of the
next trough as it pushes across the northern Plains Monday/Monday
night and results in minor surface low development. The 00Z ECMWF
by contrast shears the middle trough and ejects it from the Great
Lakes, allowing rapid trough/low development over the Upper
Midwest/Great Lakes Monday night into Tuesday. This deepening low
then closes off and tracks northeast over eastern Canada into
Wednesday night/into Day 7. Given this deterministic difference,
ensemble means are brought into the blend a bit sooner than normal
with the 06Z GEFS/00Z ECENS (which agree on general troughing
instead of closed lows) receiving weight in the WPC blend Monday
night and the dominant source by Wednesday night/Day 5 into Day 6.
This results in a much weaker low than the deterministic 00Z ECMWF
for Tuesday and Wednesday.

This weight toward ensemble means starting on Day 4 also works for
the next trough reaching the West Coast Tuesday night.


Weather Highlights/Threats:

The active pattern into the northwestern CONUS keeps the Pacific
Northwest and northern Rockies in repeating precipitation through
at least the middle of next week. This precipitation will focus
over coastal locations and the Coastal Range/Cascades and result
in a heavy rain threat for areas below the snow level. The
magnitude and placement of snow around the Great Lakes and
potential heavier rain over the already saturated TN Valley
depends on the evolution of the trough/surface low development
across the Central U.S. Tuesday and Wednesday. Confidence remains
low on the central CONUS precipitation.

With a fast west-to-east flow across the country, no strong
outbreaks of arctic air are anticipated.  This will lead to
generally near and above normal temperatures across the CONUS
through the midweek.

Jackson

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Fri Jan 03 2020

Valid 12Z Fri Jan 03 2020 - 12Z Sun Jan 05 2020

  • Locally heavy rain and thunderstorms across the Central Gulf Coast to the Carolinas today
  • Light to moderate snow expected for portions of the Midwest to Northeast
  • Precipitation continues in the Pacific Northwest through the weekend with high winds possible in the Northwest

An upper-level trough over the central U.S. will move across the eastern
U.S. over the next couple of days, along with a couple of fronts at the
surface. Rain will spread across portions of the East today as ample
moisture streams in ahead of these features. Locally heavy rainfall,
isolated flash flooding, and a few strong thunderstorms are possible
across portions of the Southeast in particular, and some rain will spread
from the Lower Mississippi Valley northeastward into the Ohio and
Tennessee Valleys, Mid-Atlantic, and Northeast. Temperatures will be mild
today, with record maximum temperatures in the 70s and 80s possible today
in Florida into the Georgia and Carolina coast.

A clipper system will track across the Midwest today, bringing light to
locally moderate snow to the Upper Mississippi Valley. As upper-level
energy continues eastward, snow is expected to spread over the interior
Northeast and higher elevations of the Central Appalachians on Saturday.
Snow totals of 3 to 5 inches are currently forecast.

Farther west, a strong frontal system is forecast to push through the
Pacific Northwest Friday night and quickly southeastward across the
Rockies and Great Basin Saturday. This will lead to increasing
precipitation; higher elevation snow could be heavy in the Cascades and
Coastal Range with snow in the Northern Rockies as well. Lower elevations
should remain rain. High winds are also likely in the West with a potent
upper-level system and the aforementioned front. High Wind Watches and
Warnings and Wind Advisories are currently in place for portions of the
Pacific Northwest and the Northern and Central High Plains.

Tate

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-------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Fri Jan 03 2020

Valid 12Z Mon Jan 06 2020 - 12Z Fri Jan 10 2020

Overview/Guidance Assessment:

The latest model/ensemble consensus displays a progressive mean
pattern aloft with embedded features of varying amplitude
extending from the short range time frame into the medium range
forecast.  Then by the later half of next week guidance indicates
development of a large scale west-central U.S. mean trough as one
ridge builds over the Pacific around 140-160W and another builds
off the southeastern U.S..  This pattern is likely to extend well
beyond the end of the period in light of the CPC 8-14 day
forecast.  
For the medium range period there is reasonable
agreement regarding the mean flow but discrepancies exist for some
important shortwave details--in particular for a system expected
to develop over parts of the East around Tue-Wed.

Regarding this potential system that may reach over or offshore
the Northeast by midweek, the multiple pieces of energy that may
be involved contribute to significant depth/track/timing
differences among model/ensemble solutions, and thus lower than
average confidence for specifics.  One influence may be energy
over Lake Superior and Ontario at the start of the period on Mon. 
Recent GFS runs have tended to be the slowest and most closed with
the energy though with the 00Z run nudging a little faster. 
Upstream energy that provides the primary dynamic support for
surface development involves two streams with various ideas in the
guidance for exact interaction/evolution.  As a result models and
ensemble members vary widely for the system's depth and track at
any particular time.  An intermediate solution appears best given
the low confidence in any specific piece of guidance.

The next meaningful shortwave in the series should approach the
West Coast on day 4 Tue with most differences generally within the
typical error range into midweek.  This energy will likely support
a wavy front crossing the central/east-central U.S. by Thu-Fri
with details requiring more time to resolve.  By day 7 Fri there
is a signal in some guidance for additional shortwave energy to
approach the Northwest.  Latest GFS runs have been noticeably
stronger than most other solutions (aside from a couple ECMWF runs
from 1-2 days ago).  The combination of detail uncertainties over
both areas would recommend an increased tilt toward ensemble means
late in the week.

In order to achieve the desired forecast over areas of interest,
the starting blend used a multi-model approach for about the first
half of the period and then steadily increased ensemble weight
(12Z NAEFS/ECMWF means) so that the means had 70 percent emphasis
by day 7 Fri.  GEFS means have been on the weak side versus other
means for the northeastern system and CMC mean input helped to add
some definition for the NAEFS mean.


Weather Highlights/Threats:

Flow coming into the Northwest will focus highest totals of
rainfall/mountain snow over favored coastal terrain along the
northern half of the West Coast and the Cascades.  Some multi-inch
liquid totals for the full five-day period are possible over the
Pacific Northwest.  Significant though somewhat less extreme
amounts are possible over the northern Rockies.  Expect
lighter/more scattered activity over the southern half of the
West.  Cooler than normal highs should prevail over parts of the
Rockies most of the period, with expansion of below normal
anomalies over the West late in the week as mean troughing aloft
becomes established.

Precipitation will likely expand in coverage over the East during
Tue-Wed as developing low pressure heads into or near the
Northeast.  Guidance spread thus far has made it difficult to
resolve precise impacts, but some solutions would produce
significant precipitation and a period of strong winds.  Precip
type is also uncertain at some locations.  Currently the best
potential for at least some snow extends from the Lower Great
Lakes/Ohio Valley/south-central Appalachians into the Northeast.

Areas over the east-central U.S. should see increasing
precipitation by next Thu-Fri as the large scale pattern evolves
toward a west-central U.S. trough aloft with a wavy surface front
reaching the central U.S..  Low level flow from the Gulf may help
to enhance rainfall totals in the warm sector.  Wintry weather is
possible over northern latitudes.

A majority of the U.S. east of the Rockies will see above normal
temperatures during the period but with some pockets of below
normal readings such as in the Upper Midwest.  Precise evolution
of the midweek Northeast system will influence temperatures as
well.

Rausch

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Sun Jan 05 2020

Valid 12Z Sun Jan 05 2020 - 12Z Tue Jan 07 2020

  • Multiple periods of precipitation are forecast for the Northwest
  • Light to moderate snow expected for the Great Lakes and interior Northeast

An active weather pattern will continue for the northwestern U.S., with a
cold front moving through today and a warm front approaching on Monday.
This will lead to rounds of precipitation there, with locally heavy
rainfall and localized flooding possible in lower elevations by of the
Pacific Northwest by Monday. Then in higher elevations of the Cascades and
Rockies, snowfall could be measured in multiple feet.

A low pressure system will move across the Great Lakes region over the
next couple of days, so snow is likely to spread across the Great Lakes
and the interior Northeast. Snowfall of 3 to 6 inches is forecast, with
locally higher amounts. On the backside of this frontal system, high winds
are expected over parts of the Northern and Central Plains into the Upper
Mississippi Valley. High Wind Warnings and Wind Advisories are in place
for these areas. Other windy areas are expected to be Piedmont east of the
Southern/Central Appalachians, as well as Southern California.

Most of the continental U.S. will have around or above average
temperatures over the next couple of days. Florida is expected to be one
cooler than average spot, where temperatures should remain near or less
than 70 degrees for highs.
Then the Central Rockies could be several
degrees below average by Monday.

Tate
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-------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Sun Jan 05 2020

Valid 12Z Wed Jan 08 2020 - 12Z Sun Jan 12 2020

  • Heavy rain potential Fri into the weekend from the Lower Mississippi Valley to the Ohio Valley

Overview/Guidance Assessment:

Latest guidance continues to advertise an amplified mean trough
aloft settling over the western U.S., between strengthening ridges
over the east-central Pacific and off the Southeast U.S..
 The
Climate Prediction Center 8-14 Day forecast still suggests some
variation of this pattern may persist well beyond the end of the
medium range period.  Evolution aloft and associated surface
features will lead to a heavy rain threat most likely from the
Lower Mississippi Valley through the Tennessee Valley and Ohio
Valley.  Teleconnections relative to the positive height anomaly
center which multi-day means show near or offshore the East Coast
later in the period also target this area for greatest
precipitation potential.  Meanwhile North Pacific energy feeding
into the mean trough will bring episodes of enhanced precipitation
with best focus over the Pacific Northwest.

Near the start of the period on Wed the models and ensemble means
have gravitated to the idea started by some solutions yesterday
that deepening low pressure off the New England coast will trace a
wide enough arc to keep a majority of the associated moisture just
offshore.  Guidance has not behaved well for this system thus far
due to evolution being dependent on important small scale details
aloft so further adjustments could still be possible.

Farther west there is reasonable agreement that a shortwave will
reach the western states by early Wed, progressing eastward while
additional energy arrives Thu.  Ejection of the leading energy and
possible interaction with southern Canada flow should lead to a
surface wave that tracks from the Plains northeastward into Canada
Thu onward.  The latter shortwave will progress across the
Southwest/southern Rockies late in the week with solutions
diverging for timing especially after early Fri.  Although the new
00Z GFS has slowed a bit, it continues to bring the shortwave more
aggressively into the eastern U.S. than most other guidance
including the GEFS mean.  Preference remains with a non-GFS
evolution that maintains greater integrity of positive height
anomalies near the East Coast.  On the other hand yesterday's 00Z
and 12Z ECMWF runs may become a bit slow and confidence is low
that the ejecting energy will consolidate in a way that ECMWF/CMC
runs show by day 7 Sun.  As a result the ensemble means become the
best option for the manual forecast valid next weekend.

At least into day 6 Sat the guidance is becoming better clustered
in principle for upper trough energy that drops into the Northwest
by early Sat and expands over the West through Sun.  Interestingly
by day 7 Sun the new 00Z GFS shows less amplitude on the southwest
side of the trough versus consensus, in contrast to a number of
previous runs that had been digging the trough a bit westward of
the majority.  GEFS/ECMWF means, the 12Z ECMWF, and new 00Z CMC
cluster fairly well.  At the surface there is still a moderate
amount of model/ensemble spread (similar to yesterday) for low
pressure that tracks into southern British Columbia and/or the
Pacific Northwest Fri/Sat--favoring maintenance of an intermediate
path.

Early in the period a model blend with more 18Z GFS/12Z ECMWF
weight than the 12Z CMC/UKMET best represented consensus for
significant features with day 5 Fri being the transition day that
started to incorporate the 18Z GEFS/12Z ECMWF means.  Days 6-7
Sat-Sun trended increasingly toward the means given questionable
attributes of the GFS after early Fri and the ECMWF by late in the
weekend.  The overall theme of the forecast maintains good
continuity with some typical run-to-run detail adjustments.


Weather Highlights/Threats:

In spite of lingering uncertainties in the specifics, confidence
is increasing for the potential of a heavy rainfall event from the
Lower Mississippi Valley into the Tennessee Valley and Ohio Valley
late this week into the weekend.
 The cold front trailing from
late week Plains-southern Canada system should have one or more
embedded waves and may progress fairly slowly for a time while
awaiting upstream western energy aloft.  Two or three days of Gulf
inflow ahead of this wavy front would provide considerable
moisture to enhance rainfall amounts and some embedded convection
is possible.  This area encompasses some locations that recently
received significant rainfall so effects from this upcoming event
will require close monitoring.
 There is still a signal for some
wintry precipitation on the northern periphery of the moisture
shield but so far with fairly low probabilities of significant
accumulations.

Over the West, continue to expect highest totals of rain/mountain
snow over the Pacific Northwest coast/northwest corner of
California as well as the Cascades, with a secondary maximum over
the northern Rockies.  Some moisture will extend southeastward but
with lighter amounts in most cases.  Heaviest precipitation should
occur from Fri or Fri night into the weekend, though amounts are
likely not to be extreme given fairly modest precipitable water
anomalies.

The aforementioned Plains-southern Canada system may produce some
precipitation over parts of the Upper Midwest and Great Lakes but
with some dependence on system strength that has yet to be fully
resolved.  Some activity should accompany the trailing front as it
reaches the Northeast.  Earlier in the period, the system tracking
off the New England coast on Wed will strengthen as it heads into
the Canadian Maritimes.  Based on current forecast most areas
should see modest amounts of precipitation but there will be a
brief period of breezy conditions in its wake.

Expect highs to be 5-15F below normal on average from the northern
Plains through much of the West during the period.  Colder air may
drop into Montana toward the end of the period next Sun.  Warmth
will overspread the eastern half of the country with some
anomalies likely to exceed plus 20F, especially for morning lows.

Rausch

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
253 AM EST Mon Jan 06 2020

Valid 12Z Mon Jan 06 2020 - 12Z Wed Jan 08 2020

  • Persistent precipitation is forecast for the Pacific Northwest
  • A couple rounds of light to moderate snow expected for the Great Lakes and Northeast
  • Light snow possible from the southern Appalachians to the Mid-Atlantic on Tuesday

An active weather pattern will continue for the northwestern U.S., as a
warm front will pass through today ahead of a cold front expected to move
through Tuesday evening. Plenty of moisture flowing into the region could
lead to locally heavy rainfall and localized flooding in the lower
elevations of western Washington and northwestern Oregon today. Across
higher elevations of the Cascades and Northern Rockies, snowfall should be
measured in multiple feet. Lighter snow accumulations are possible in the
Northern High Plains.

A low pressure system is forecast to track across the interior Northeast
today, which will spread snow across that area. Snowfall should be
generally light, except for downwind of Lake Ontario where lake
enhancement will lead to higher totals of over 6 inches. Tonight into
Tuesday, another frontal system is expected to move across the Upper Great
Lakes region, causing another round of light snow. Meanwhile farther
south, a low pressure system is forecast to begin strengthening across the
Tennessee Valley and track across the Mid-Atlantic and offshore.
Precipitation is forecast in the vicinity of this low, with light rain in
the Tennessee Valley and snow developing in the Southern/Central
Appalachians tonight into Tuesday morning.
As the low tracks
northeastward, light snow could spread across portions of the Mid-Atlantic
on Tuesday. By Tuesday night and Wednesday, both of these low systems will
contribute to light snow across the Northeast.

The bulk of the continental U.S. is forecast to have near to above average
temperatures over the next couple of days. But Florida will have one more
cooler than average day today, with highs in the 60s and low 70s. Frost
Advisories are in place for portions of southern Georgia and northern
Florida.
The Central Rockies could be several degrees below average on
Monday also. Then on Tuesday into Wednesday morning, a cold front will
lead to below average temperatures for the north-central tier.

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------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Mon Jan 06 2020

Valid 12Z Thu Jan 09 2020 - 12Z Mon Jan 13 2020

  • Heavy Rain Threat from the Lower-Mid Mississippi Valley into Tennessee/Ohio Valleys Fri-Sat
  • Active pattern over the Northwest

Overview/Guidance Assessment:

There are embedded details that exhibit some spread and
variability but guidance agrees that strong ridges aloft over the
east-central Pacific and off the southeastern U.S. coast will hold
in place an amplified western U.S. trough at least into early next
week.  Within this pattern, low level flow of Gulf moisture ahead
of an ejecting western shortwave/leading wavy cold front will
produce an episode of heavy rainfall from parts of the Lower-Mid
Mississippi Valley eastward/northeastward from late this week into
the weekend with some wintry weather on the northern side of the
precipitation shield.  Meanwhile energy flowing around the
northeastern side of the Pacific ridge will bring a series of
systems into the Northwest.  The trajectory of moisture across the
Northeast Pacific is not favorable for extreme precipitation
totals but the accumulations over several days may still be
significant.

One of the most problematic aspects of the forecast in recent days
has been the timing/evolution of shortwave energy reaching the
West Coast around the start of the period early Thu and ejecting
from the West after Fri.  For the moment solutions are much closer
together than they had been, by way of the GFS hedging a bit
slower/less amplified as the shortwave crosses the eastern half of
the lower 48 and the 12Z ECMWF trending significantly faster/more
open than a number of previous runs.  CMC runs continue to hold
onto a somewhat slower and more closed feature aloft until it
reaches past the Mississippi Valley.  Ensemble means are still a
bit slower than the non-CMC cluster but provide added support for
an open wave.  An early look at the new 00Z ECMWF reveals a
slightly slower trend, highlighting the ongoing uncertainty.  The
latest guidance cluster would still produce a significant heavy
rain event over the east-central U.S. but a modestly shorter
duration would temper the highest totals somewhat.

Upstream the guidance spread appears to have narrowed somewhat for
the storm system forecast to track into Washington/southern
British Columbia Fri-Sat.  There are still meaningful
medium/smaller scale shortwave differences yet to be resolved so
convergence of solutions may be a slow process.  The energy aloft
will overspread the western U.S. with time with some of it
possibly reaching the Plains and supporting one or more surface
waves by the start of next week.

By the latter half of the period there is some spread over exactly
how western Canada energy may descend toward the western
U.S.-Canada border.  The 00Z GFS backed off from the 516dm contour
upper low that the prior two runs had just north of Montana on day
7 Mon but is still deeper than most other models/means over that
area.

A multi-model blend with greater emphasis on the 12Z ECMWF and
12-18Z GFS relative to the 12Z UKMET/CMC provided a reasonable
depiction of consensus for the first half of the period, while
increasing detail uncertainties by days 6-7 Sun-Mon recommended
about 50-60 percent total weight of the 18Z GEFS/12Z ECMWF means
along with lingering input from the ECMWF/GFS runs.

Weather Highlights/Threats:

A system tracking from the northern Plains into eastern Canada
late in the week will spread precipitation across the Great Lakes
and Northeast with some wintry weather possible across northern
parts of these regions.

Confidence is still above average for the overall heavy rainfall
event expected from parts of the Mid-Lower Mississippi Valley into
the Ohio/Tennessee Valleys during the late week into weekend time
frame.  However uncertainty with the timing of supporting dynamics
ejecting from the West provides some challenge for resolving the
rainfall duration and highest totals.  The scenario continues to
be favorable with a feed of Gulf moisture interacting with an
approaching wavy front, producing areas of heavy rain/embedded
convection.  The Storm Prediction Center is also highlighting a
potential for severe weather across the southern tier of states
with this event.  Some locations within the heavy rainfall threat
area have recently received significant rainfall so effects from
this upcoming event will require close monitoring.  Meanwhile over
the past day the signal for wintry precipitation on the northern
periphery of the moisture shield has strengthened.  Primary snow
potential should extend from parts of the Midwest through the
Great Lakes and Northeast.  The wavy cold front will eventually
cross the East Coast and extend into the Gulf.  This trailing part
of the front is likely to return north as a warm front around the
start of next week and become one focus for another potential
rainfall event near the end of the medium range period and beyond.

The series of systems coming into the Northwest will focus the
highest rain/mountain snow totals over the Pacific Northwest
coast/northwest corner of California along with the Cascades. 
Expect a secondary maximum over the northern Rockies.  At times
moisture will extend southeastward into the Sierra Nevada/Great
Basin/Central Rockies but with lighter amounts in most cases. 
Amounts should not be extreme given that northwesterly flow should
promote only modest anomalies for deep moisture, but multi-day
totals over the most favored terrain could reach a few inches
liquid.

From late week into the weekend expect a surge of very warm air to
extend from the central through eastern U.S. with a broad area of
plus 10-25F anomalies for highs and plus 20-30F and locally higher
anomalies for morning lows.  Some daily records are possible,
especially for warm lows.  Most of the West will see moderately
below normal highs through the period.  The extreme northern
Plains/Montana will be a focus for some colder anomalies,
including some readings 20-30F below normal Sun-Mon.

Rausch

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
201 PM EST Tue Jan 07 2020

Valid 00Z Wed Jan 08 2020 - 00Z Fri Jan 10 2020

  • Heavy precipitation continues for the Northwest
  • Snow possible across the Southern/Central Appalachians, the Mid-Atlantic and the Northeast

The Pacific Northwest will continue to be in an active wet pattern with
scattered to widespread coastal rains and mountains snows. Durations of
moderate to heavy rainfall along with localized flooding will be possible
in the lower elevations of western Washington and the Northern Rockies. In
some place, accumulations may reach or exceed 1 foot. Winter storm
warnings and winter weather advisories area scattered across parts of this
region. Recent temperatures across parts of northern Idaho and extreme
northwest Montana have caused unstable snow pack conditions. With the
addition of potentially several inches of new snow, there is an increased
threat for avalanches. As such, there are Avalanche warnings in effect.
As
the cold front tracks further through the Rockies and out into the Plains
by Thursday, showers and thunderstorms will overspread the Mississippi
Valley ahead of its arrival. Another round of precipitation will begin to
move onshore the Pacific Northwest by late Thursday and continue into the
weekend, spreading the snow across the Intermountain West/Rockies and into
portions of the Great Basin. For additional details, please refer to the
Extended Forecast Discussion and the Heavy Snow and Icing Discussion.

A surface low pressure system will strengthen as it crosses the Southern
and Central Appalachians this afternoon. Precipitation will spread from
the Carolinas, Mid-Atlantic to the Northeast as it moved eastward. A mixed
bag of precipitation is expected with this low, with mainly rain hugging
the coastal areas quickly transitioning to a mix or all snow. Winter
Weather Advisories are in effect for portions of the Mid-Atlantic and
southern portions of the Northeast through tonight. Generally light snow
should spread into the Northeast on the backside of this low and as
another frontal system moves through tonight into Wednesday.

Temperature-wise, most of the country will be at or above average today,
with cooler than average temperatures confined to parts of the Central
Great Basin and the north-central U.S. Then below average temperatures
spread to the Great Lakes region on Wednesday, with temperatures cooling
along the West Coast as well.

Campbell

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--------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1256 PM EST Tue Jan 07 2020

Valid 12Z Fri Jan 10 2020 - 12Z Tue Jan 14 2020

  • Late week/weekend storm to bring a heavy rain threat to the Ark-La-Tex region/Lower-Mid Mississippi Valley and northeastward
  • Possible severe weather to parts of the South
  • Wintry precipitation potential to the central Plains/Midwest through Great Lakes/Northeast
  • Active pattern over the Northwest


18 UTC Update:

No major changes to the ongoing forecast were made during this
update. A blend relying heavily on the 00Z ECMWF/UKMET/06Z GFS was
used during days 3-5 (Fri-Sun). Quite a bit more emphasis was
placed on the ECMWF/UKMET relative to the GFS. The GFS was weaker
and faster than the overall consensus with the surface low
expected to develop across the lower Mississippi Valley Fri
night/Sat, which is then expected to track northeastward across
New England on Sun. The ECMWF/UKMET solutions were much better
clustered with the ensemble means in showing a slower and somewhat
deeper low pressure system, and these solutions were preferred.
The trend toward greater confidence in these solutions resulted in
a relatively small westward shift in the heaviest QPF amounts
during the day 4-5 time frame.

Later in the forecast period the GFS continued to differ from the
ECMWF and from the overall ensemble consensus. The GFS was weaker
with the subtropical ridge across the Southeast by early next
week, which results in a more suppressed and faster-moving low
pressure system across the southern tier Mon-Tue. Given the
evolution of the large-scale/hemispheric pattern, with a building
anomalous upper ridge between Alaska and Hawaii, this favors a
persistent mean trough along the U.S. West Coast and a stronger
subtropical ridge in the Southeast.
The ECMWF was much closer to
this idea, and has, for a couple runs, shown an area of low
pressure developing across the Southern Plains by Mon and moving
northeast toward the Ohio Valley or Great Lakes by Tue. Ensemble
means also show a fair degree of support for this idea. Given that
this solution is also supported by hemispheric teleconnections,
opted to continue using about 30 percent of the 00Z ECMWF through
day 7 along with the remainder comprised of ECENS/GEFS ensemble
means.

Ryan

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Wed Jan 08 2020

Valid 12Z Wed Jan 08 2020 - 12Z Fri Jan 10 2020

  • Frontal system spreads cooler temperatures and precipitation from west to east Wednesday and Thursday
  • Light snow expected for the Great Lakes region to Northeast today

A low pressure system is forecast to track across the Northern Rockies to
Northern Plains today, moving into the Upper Midwest on Thursday. This
will sweep a cold front across the western and central U.S. ahead of an
upper-level trough. Today, snow is likely for the Northwest, with some
lower elevation rain continuing for the Pacific Northwest. Tonight into
Thursday, another surface low will move southeastward into California,
helping cause additional lower elevation rain and higher elevation snow in
much of the West. Snowfall totals over the next two days could approach a
foot in the Cascades, Northern Rockies, and into the Tetons/Wind River
Mountains. Avalanche Warnings are in place for northern Idaho and far
northwestern Montana due to the recent high snow totals. Lighter
precipitation is forecast for California, the Great Basin, and the
Southwest.

As the cold front progresses into the central U.S. on Thursday, showers
and thunderstorms will begin ramping up ahead of the front as moisture
returns from the Gulf of Mexico. Some locations from the Lower/Middle
Mississippi Valley to the Ohio Valley could receive up to an inch of rain
through Friday morning, but heavier precipitation will continue into the
weekend.
The cold front will lead to cooler than average temperatures for
the West Coast to the Rockies by Thursday. Much warmer than average
temperatures are forecast in the Central/Southern Plains and Middle/Lower
Mississippi Valley both today and Thursday, and the Upper Midwest to Great
Lakes region should warm up significantly on Thursday after a chilly day
today.

Farther east, a frontal system is expected to pass through the Lower Great
Lakes to Northeast, leading to some snow there today. Snow totals should
remain light. Elsewhere, fire weather conditions are expected to be
elevated across portions of the Southern/Central Plains today and Thursday
with gusty winds and dry conditions.


Tate
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-----------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Wed Jan 08 2020

Valid 12Z Sat Jan 11 2020 - 12Z Wed Jan 15 2020

  • Eastern U.S. storm this weekend to bring a heavy rain threat to lower half of the Mississippi Valley and areas to the east/northeast
  • Severe weather potential to parts of the South
  • Wintry precipitation to the Midwest through Great Lakes/northern New England
  • Active pattern over the Northwest

Overview/Guidance Assessment:

Into the first part of next week guidance is consistent and
agreeable in showing persistent and amplified western U.S. mean
troughing between strong ridges off the Southeast U.S. and over
the east-central Pacific.
 This pattern will support at least a
couple significant precipitation events over parts of the eastern
half of the lower 48.  The first will be a widespread event
associated with low pressure tracking from the Mid-Lower
Mississippi Valley through the Northeast this weekend.  Additional
events next week have a less-defined focus at this time and thus
have lower confidence in specifics, with best signals for highest
rainfall totals over the interior Southeast.
 Multiple systems
reaching the Northwest will produce significant precipitation over
favored terrain in terms of five-day totals.  There will be a
pronounced temperature contrast between much above normal
temperatures over the East and much below normal temperatures
overspreading the northern Plains and to a lesser extent the
northern/central portions of the West.

Guidance is still in the process of resolving the evolution of the
shortwave/surface low tracking northeastward from the
Plains/Mississippi Valley through the Northeast this weekend.  In
the latest runs through 12Z/18Z as well as the new 00Z cycle
solutions have generally sorted themselves into two clusters, with
the ECMWF/ECMWF mean/CMC/UKMET and some other models depicting an
occluded (or nearly so) surface system by early day 4 Sun with
timing slower than the sheared GFS/GEFS mean.  Progression of the
southeasterly mean flow keeps the door open for timing that is a
bit faster than the ECMWF cluster but overall there is too much
consensus to incorporate the GFS scenario in the manual forecast.

Upstream flow, with another shortwave progressing into the West,
shows reasonable agreement into day 4 Sun.  However after that
time the models/ensembles begin to go astray regarding the timing
and amplitude of this western energy once it continues beyond the
Rockies as well as for upstream impulses.  Thus there is very poor
agreement over specifics of one or more surface waves that should
emerge over the Plains and continue to the east/northeast.  Then
around Tue-Wed larger scale model discrepancies develop with
respect to how North Pacific energy could begin to dampen the
east-central Pacific upper ridge.  Downstream effects may reach
the western U.S. by day 7 Wed.

Over recent days the guidance has varied with details of western
Canadian flow aloft that should dip into the northern parts of the
West/Plains and support the forecast trend toward colder
temperatures over this area.  In differing ways the GFS and CMC
runs have tended to bring lower heights to areas near the
U.S.-Canadian border than most other guidance.

Forecast preference early in the period led to starting with a
blend of the 12Z and 00Z ECMWF along with the 12Z UKMET/CMC/ECMWF
mean for days 3-4 Sat-Sun.  This blend toned down the specific 12Z
ECMWF solution that appeared too deep/westward within the
otherwise favored cluster for the eastern U.S. system.  After this
system's departure the blend could then incorporate some 18Z
GFS/GEFS mean input along with maintaining the ECMWF runs and
ECMWF mean.  Low confidence in details favored increasing total
ensemble weight to 50-70 percent by late in the period.


Weather Highlights/Threats:

Heavy rainfall expected to be in progress over/near the Mid-Lower
Mississippi Valley at the start of the period early Sat should
continue to the east/northeast during the weekend as low pressure
tracks from the Mississippi Valley through the Northeast.  In
addition to the heavy rainfall, expect this system to produce a
severe weather threat across portions of the South.  Check latest
Storm Prediction Center products for updated information regarding
the severe weather forecast.
 Meanwhile winter weather will be
likely on the cold side of the system.  The current winter weather
outlook highlights an axis from near Missouri through the central
Great Lakes and northern New England for the best potential of
meaningful snowfall.

Additional waves emerging from the Plains may promote the
stalling/northward return of the front trailing from the above
weekend system.  However wave specifics are very unclear at this
time.  As a result confidence is moderate to low regarding the
next possible heavy rain event.  Currently the best signal extends
from the Lower Mississippi Valley into the southern Mid-Atlantic
with highest totals over the interior Southeast.  
Lighter
precipitation will be possible farther to the north/northeast,
snow over northern latitudes and mostly rain farther south.

Over the Northwest continue to expect repeated episodes of rain
and mountain snow with highest five-day totals focused along
favored terrain of the Cascades and Pacific Northwest
coast/northwest California.  The northern Rockies will see a
secondary maximum of snow while areas from the Sierra Nevada into
the central Rockies will see somewhat lower totals.  By the middle
of next week forecast specifics become more uncertain as eastern
Pacific flow differences range between persistence of the pattern
with another system reaching the Pacific Northwest (currently
preferred based on the ensemble means) or a farther offshore
system that would allow for a break in the precipitation.

Gradually lowering heights aloft along the central/western
U.S.-Canadian border will lead to much below normal temperatures
spreading over an increasing portion of the northern Plains and
West.  The core of coldest air should be over/near Montana with
some readings 30-40F below normal by early next week.  Northern
parts of the West may see highs 10-20F below normal by early-mid
week.
 Eastern U.S. warmth should be the most extreme this weekend
ahead of the Mississippi Valley through Northeast system, with
widespread plus 20-35F anomalies that may reach/exceed daily
records for highs and/or warm lows.  Even after the system's
passage temperatures should remain 10-20F above normal for highs
with some higher anomalies for morning lows. 

Rausch

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
312 AM EST Thu Jan 09 2020

Valid 12Z Thu Jan 09 2020 - 12Z Sat Jan 11 2020

  • Heavy rain, flash flooding, and severe weather will ramp up on Friday in the central U.S. ahead of a developing low pressure system
  • Light snow and freezing rain are possible for portions of the Plains, Mississippi Valley, and Great Lakes
  • Colder than average for the West Coast to Northern Plains and much warmer than average in the eastern half of the nation
  • Heavy snow once again possible in higher elevations of the Northwest Friday into Saturday

An upper-level trough over the western half of the contiguous U.S. will
strengthen tonight and Friday as additional energy comes in. A frontal
system at the surface will move slowly through Friday as the trough
develops, before both features move eastward this weekend. Moisture from
the Gulf of Mexico will flow into the vicinity of the fronts, leading to
increasing rain chances today and especially on Friday for the Southern
Plains into much of the Mississippi and Ohio Valleys. After rainfall of up
to an inch in those areas today into tonight, rainfall totals are forecast
to be 3 to 5 inches on Friday and Friday night in a swath from far
northeastern Texas to eastern Oklahoma, northwestern Arkansas, and
southwestern Missouri. Thus, there is a Moderate Risk of flash flooding in
those areas for Friday. Flood and Flash Flood Watches are in effect across
much of Missouri, Illinois, and Indiana ahead of the rainfall.
Additionally, the Storm Prediction Center has outlooked an Enhanced Risk
of severe weather on Friday for parts of the Southern Plains to Lower
Mississippi Valley.

On the backside of this system, light to moderate snow is expected in the
Intermountain West and Rockies today, spreading eastward tonight and
Friday. A wintry mix of snow, sleet, and freezing rain is possible in
portions of the Southern/Central Plains into the Middle Mississippi Valley
and northeastward into the Great Lakes region Friday into Saturday after
the cold front drops the temperatures. Freezing rain amounts of over a
tenth of an inch are currently forecast for parts of Missouri into
southeastern Iowa.

The strong front will also lead to significant temperature anomalies
across the country. Ahead of the front, high temperatures will be 15 to 25
degrees above average from the Plains into the Mississippi, Ohio, and
Tennessee Valleys today, with low temperatures Friday morning more than 30
degrees above normal over a large part of that area--widespread record
high minimum temperatures are expected to be set over the next couple of
days. The Eastern Seaboard will join in on the warmth on Friday. Colder
than average temperatures are forecast for the western half of the
country, however, due to the first front and a secondary cold front which
is expected to reinforce the cold air. By Friday, high temperatures in the
single digits are forecast for the north-central tier of the nation.     

Another low pressure system is forecast to approach the Northwest on
Friday, which combined with more upper-level energy will lead to heavy
precipitation. Rain is forecast for lower elevations of the Pacific
Northwest, with snow elsewhere from the Cascades to the Northern Great
Basin and Northern Rockies. Through Friday night, heavy snow of over 2
feet is expected in higher elevations of the Cascades, with the Northern
Rockies expecting snow totals in excess of a foot.

 

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--------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EST Thu Jan 09 2020

Valid 12Z Sun Jan 12 2020 - 12Z Thu Jan 16 2020

  • Significant late week/weekend system affecting the eastern U.S. to cross the Northeast on Sunday
  • Active pattern over the Northwest, possibly starting to extend southward after midweek

Overview/Guidance Assessment:

Latest guidance is still suggesting that during next week the
large scale pattern may begin to evolve away from the amplified
configuration consisting of a western U.S. trough and strong
east-central Pacific/western Atlantic ridges.
 This will occur as
the initial east-central Pacific ridge collapses in favor a ridge
building into the Bering Sea and mainland Alaska while the western
Atlantic ridge flattens while its center gravitates to near Cuba. 
The gradual trend toward flatter flow across the lower 48 will
tend to keep best potential for heaviest eastern U.S.
precipitation totals over the Southeast near a persistent frontal
boundary
while a series of fast-moving Pacific systems will
continue to focus the greatest western U.S. activity over the
Pacific Northwest/northwest California and northern Rockies. 
Specifics of flow aloft become uncertain by the end of the period
next Thu but moisture should start sagging southward toward
central California.  Low heights heights aloft crossing areas near
the western-central U.S.-Canadian border (likely anchored by an
upper low crossing southern Canada) will play a role in the much
below normal temperatures forecast over the northern Plains and
extending into the northern parts of the West to a lesser extreme.
 Much above normal temperatures will persist over the eastern U.S.
but with decreasing coverage by next Thu.

Models/ensembles are finally developing a more robust consensus
for the evolution of the system crossing the Northeast on Sun. 
This is due to the previously fast/sheared GFS adjusting back to
established consensus from the past day or so indicating an
occluded system over the eastern half of the Great Lakes region as
of 12Z Sun.  The 18Z GFS was still a bit fast but close enough to
include as a minority input for the blend but the new 00Z GFS and
GEFS mean have completed the trend to the majority cluster.

Farther upstream the guidance depicts a rapidly moving series of
Pacific shortwaves feeding into and then ejecting from the western
U.S. mean trough aloft.  There has been decent clustering for
identifying each feature as it comes into the West Coast but
models/ensembles have had a difficult timing resolving how each
impulse will reflect at the surface to the east of the Rockies. 
Thus confidence remains lower than average for specifics over the
central/eastern U.S. during the first half of next week.  By late
in the period a more coherent signal seems to arise, toward low
pressure crossing southeast Canada and/or New England (albeit with
some timing spread) and a trailing front reaching the
southern/eastern states.

By next Wed-Thu the main focus over the West will be a fairly
strong storm system forecast to approach the West Coast. 
Currently the majority cluster includes the GFS/GEFS mean/CMC/CMC
mean/ECMWF mean which all suggest that the past couple ECMWF runs
may be too fast to bring the system inland.  Looking at
larger-scale flow, teleconnections relative to the upstream
ridge's positive height anomaly center suggest that recent GFS
runs may be pulling the core of downstream troughing too far
westward in the D+8 means.  This is likely to be a greater issue
after the end of the medium range period so a minority component
of the GFS could still be used as a blend component into next Thu.

While some GFS/CMC runs may have been a bit extreme, other
solutions have been trending toward their general idea of an upper
low over southwest Canada tracking close enough to the U.S. border
to bring fairly low heights across far northern parts of the
western/central U.S. during the period.

The updated forecast consisted of an operational model consensus
early in the period and then transitioned toward increasing
GEFS/ECMWF mean weight, reaching 60 percent by day 7 Thu.  Due to
fast timing of the incoming Pacific system late in the period, the
forecast removed the 12Z ECMWF by Thu while maintaining some
GFS/CMC input.


Weather Highlights/Threats:

The system expected to track across the Northeast on Sun will
bring a potential for meaningful winter weather to northern New
England and some light-moderate rainfall just to the south.  The
front trailing from this system will settle over the Southeast
while the farthest southwest part of the front should lift from
the Gulf of Mexico into the southern U.S. as a warm front.  This
front and modest Gulf inflow should promote periods of moderate to
locally heavy rainfall over parts of the South, with some repeat
activity possibly helping to enhance totals at some locations. 

However confidence is fairly low for specifics of shortwaves
aloft/surface waves so it will take additional time to resolve
coverage and magnitude of heaviest rainfall.  Meanwhile at least
one area of light to moderate precipitation (snow over northern
areas) should spread across northern areas of the central/eastern
U.S. but again with lower than average confidence in the details.

The progression of systems affecting the Northwest should provide
the best rain/mountain snow focus over favored terrain in western
Oregon and far northwest California with meaningful precipitation
also over Washington and across the northern Rockies.  Central
latitudes of the Interior West/Rockies should see lighter
activity.  Moisture may begin to push a little farther south
toward central California around or just after the end of the
period as favored by teleconnections relative to the upper ridge
building into the Bering Sea/Alaska.  With cold air pushing
southward from Canada into northern parts of the West, there will
be increased potential for snow at very low elevations (possibly
near or at sea-level) by mid-late week.  This is reflected in the
Winter Weather Outlook probabilities valid in that time frame. 
The storm system which most guidance has approaching the West
Coast Wed-Thu will have to be monitored closely for the
possibility of significant inland/low elevation snow depending on
track and strength of the cold air push to the north.

Expanding influence of cold air across the northern tier will
bring readings 25-40F below normal over parts of the northern
Plains for multiple days next week while areas over and west of
the northern Rockies may be as cold as 15-30F below normal.  It is
close to the climatologically coldest time of year so it may take
more extreme anomalies than these to reach daily record values at
many locations.  Warmest anomalies over the East will likely be
for morning lows with fairly broad coverage of readings 20-30F
above normal.  Highs of 10-20F above normal will be common with
pockets of warmer anomalies.  Arrival of a cold front should begin
a cooling trend over the South and East by next Thu.

Rausch

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
302 AM EST Fri Jan 10 2020

Valid 12Z Fri Jan 10 2020 - 12Z Sun Jan 12 2020

  • There is a moderate risk of excessive rainfall over parts of Southern Plains, Middle Mississippi Valley, and Lower Mississippi Valley along with Moderate risk of severe thunderstorms over parts of the Southern Plains/Lower Mississippi Valley
  • Heavy snow and rain/freezing rain for parts of the Great Lakes and Upper/Middle Mississippi Valley
  • Temperatures will be 10 to 25 degrees above average over the Southern Plains/Lower Mississippi Valley into the Ohio Valley/Great Lakes
  • Heavy snow once again possible in higher elevations of the Northwest...

A deep trough over the Rockies will move eastward to the Lower Great Lakes
by Sunday.  Along the associated front heavy rain will develop from parts
of the Southern Plains northeastward to the Great Lakes producing 1 to 3
inches.  Due to the slow progression of this system, storm motion will be
slow and expected to track over the sames area.  This will become become
problematic as soils become saturated.  A moderate risk of excessive
rainfall is forecast over parts of Eastern Oklahoma and neighboring
states.  The rain will produce numerous flash flooding will occur with
many streams being flooded and floods affecting larger rivers.  
Additionally, the Storm Prediction Center has forecast a Moderate Risk of
severe weather for parts of the Southern Plains to Lower Mississippi
Valley.

On the backside of this system, light to moderate snow over the
Intermountain West and Rockies will spread eastward. A wintry mix of snow,
sleet, and rain/freezing rain is possible in portions of the
Southern/Central Plains into the Middle Mississippi Valley and
northeastward into the Great Lakes Friday into Sunday after the cold front
drops the temperatures. The heaviest rain/freezing rain is forecast over
parts of Great Lakes Saturday into Sunday.

A stark temperature gradient will setup over the country thanks to the
strong front over the Central U.S. into the Great Lakes.  In the warm
sector ahead of the front, daily temperatures will average 10 to 25
degrees warmer than typical early January readings. Numerous records are
expected to be broken from the Ohio and Tennessee Valleys into the
Northeast.  In contrast, the western half of the country will be much
colder than usual as a cold front and secondary cold front reinforces the
frigid airmass.  On Friday, high temperatures in the single digits are
forecast for the north-central tier of the nation.     

The Pacific Northwest will have another low pressure system approach the
region on Friday, which will amplify the precipitation.  Coastal areas
will have periods of moderate rain while higher elevations of the
Cascades, Northern Great Basin and the Northern Rockies will have heavy
snow.  Snow accumulations may very well reach or exceed 2 feet in the
highest peaks of the Cascades, around 1 foot elsewhere.

Ziegenfelder

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-------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EST Fri Jan 10 2020

Valid 12Z Mon Jan 13 2020 - 12Z Fri Jan 17 2020

Weather Pattern/Hazard Highlights and Guidance/Predictability
Assessment:

A closed low/trough will shift from the Canadian Rockies eastward
across southern Canada to the Canadian Maritimes Monday-next
Friday and a cold arctic airmass coincident with lower atmospheric
high pressure will spill southward through the Northwest and the
central and eastern U.S. in the wake of passage.
This offers a
threat for a swaths of snow across the U.S. northern tier of the
central and eastern U.S., albeit with mainly modest QPF.

Meanwhile underneath, an amplified mid-upper level mean trough
will periodically be reinforced with eastern Pacific energies that
dig over an unsettled western U.S. next week. WPC winter weather
outlook probabilities show a widespread snow threat over the
Northwest that may work down to lower elevations given the extent
of cold air filtration. Activity will spread down into the Sierra
and out across the north-central Great Basin/Rockies with system
progressions.

Trough energies and associated surface systems will tend to eject
east-northeastward out from the West over the central and eastern
U.S. overtop a lingering and warming/stabilizing Florida mean
ridge. There remains much uncertainty with potential cyclogenesis
scenarios in advance of the northern stream cold surge and along
lead fronts, but the pattern seems to favor the heaviest rainfall
potential next week from the lower MS Valley and Mid-South through
the Southeast overtop the shielding Florida ridge.

The latest models and ensembles are tending to converge upon a
more common solution with mid-scale systems embedded within
complex and progressive flow over the lower 48 states. This
bolsters forecast confidence a bit, but recent runs of the ECMWF
have been erratic and still offer more variance than desired.
Accordingly, the WPC medium range product suite was primarily
derived from a composite blend of the more compatible and run to
run stable 18 UTC GFS and 12 UTC ECMWF ensemble mean along with
the 00 UTC National Blend of Models. This blend maintains good WPC
forecast continuity.

Schichtel

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Sat Jan 11 2020

Valid 12Z Sat Jan 11 2020 - 12Z Mon Jan 13 2020

  • Heavy snow and rain/freezing rain over parts of the Great Lakes into parts of Northern Maine
  • There is an enhanced risk of severe thunderstorms over parts of the Central Gulf Coast
  • Slight risk of excessive rainfall over parts of the Lower/Middle Mississippi Valley into Western Ohio Valley and the Great Lakes
  • Temperatures will be 10 to 35 degrees above average over the Eastern Ohio Valley/Tennessee Valley into the Northeast
  • Heavy snow will continue over the higher elevations of the Northwest

A potent winter storm will bring multiple weather hazards to much of the
Great Lakes/Middle Mississippi Valley and portions of the Northeast. 
Severe thunderstorms, heavy rain and flash flooding will impact a vast
portion of the Central Gulf Coast/Lower Mississippi Valley into the Great
Lakes.  Snow fall of up to one foot over parts of the Great Lakes downwind
from Lake Huron with six to eight inches over parts of Wisconsin off of
Lake Michigan.  A mix of rain, freezing rain, sleet and snow is expected
from the Middle Mississippi Valley to the Great Lakes and into Northern
Maine.  Ice accumulations of 0.25 to 0.50 inches over Michigan and
Northern Maine.

Heavy rain in the range of 1 to 3+ inches is expected from the Tennessee
Valley northeastward to the Great Lakes.  Due to the slow progression of
this system, storm motion will be slow and expected to track over the
sames area.  This will become become problematic as soils become
saturated.  A slight risk of excessive rainfall is forecast over parts of
Tennessee Valley/Lower Mississippi Valley northeastward to the Western
Ohio Valley and parts of the Great Lakes.  The rain will produce scattered
flash flooding that will be mainly localized.  The most vulnerable area
will be urban areas, roads, and small streams with isolated significant
flash flooding possible.  Additionally, the Storm Prediction Center has
forecast a Enhanced Risk of severe weather for parts of the Central Gulf
Coast/Lower Mississippi Valley and Tennessee Valley.

A stark temperature gradient will setup over the country thanks to the
strong front over the eastern third of the country.  In the warm sector
ahead of the front, daily temperatures will average 10 to 35 degrees
warmer than typical early January readings
.  Numerous records are expected
to be broken from the Ohio and Tennessee Valleys into the Northeast.      

The Pacific Northwest will have another low pressure system approach the
region on Sunday, which will amplify the precipitation.   Moderate to
heavy snow will continue over the Intermountain West and Northern/Central
Rockies through Monday.  Snow accumulations may very well reach or exceed
2 feet in the highest peaks of the Cascades, around 1 foot elsewhere.  
The snow levels will drop down to the coast on Sunday into Monday over
Washington and Oregon.
 

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-----------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
135 AM EST Sat Jan 11 2020

Valid 12Z Tue Jan 14 2020 - 12Z Sat Jan 18 2020

Weather Pattern/Hazard Highlights and Guidance/Predictability Assessment

A deepened closed low/trough is still expected to shift from the
Canadian Rockies eastward across southern Canada to the Canadian
Maritimes Tuesday-Friday. A cold Arctic airmass coincident with
lower atmospheric high pressure will spill southward through the
Northwest and the central and eastern U.S.
Expect a stark
temperature contrast across this front that will divide areas with
much below and much above values that near records. Recent GFS
runs seem too aggressive with arctic air, but WPC remains settled
between the GFS and alternate guidance that may prove too benign
given the pattern. 

Meanwhile underneath, an amplified mid-upper level mean trough
will periodically be reinforced with eastern Pacific storm
energies that dig over an unsettled western U.S. next week. In
particular, guidance has trended in support of a deepened/well
organized low offshore the Pacific Northwest Wed/Thu that would
enhance maritime hazards and inland flow/weather. WPC QPFs and
winter weather outlook probabilities show a widespread snow threat
over the Northwest that may work down to lower elevations given
the extent of cold air filtration. Activity will spread down into
the Sierra and out across the north-central Great Basin/Rockies
with system progressions. Snows over the northern High
Plains/Rockies would be enhanced by periodic post-frontal lower
level upslope flows.

Upper trough energies and surface systems will tend to eject
east-northeastward out from the West over the central and eastern
U.S. overtop a lingering and warming/stabilizing Florida mean
ridge and undercutting the Arctic airmass. The preferred
GFS/ECMWF/Canadian now offer quite similar system evolutions
Tue-Thu including a deepening low from the central Plains to the
Northeast, but the UKMET does not develop the low much, so some
uncertainty lingers. There is also uncertainty with potential
cyclogenesis ahead of the northern stream cold surge along lead
fronts by day 6-7, so an ensemble mean forecast approach was used.
Overall, the pattern seems to favor moderate rainfall potential
next week from the south-central U.S. to the Appalachians overtop
the shielding Southeast ridge.
The pattern also offers a
widespread snow/ice threat in the cooled northern tier of the
central and eastern U.S. as deepening frontal waves wrap moisture
into the region, especially Wed/Thu and then again with more
uncertainty heading into next weekend. This threat is also shown
by WPC progs, grids, QPFs and winter weather outlook
probabilities.

Schichtel

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
302 AM EST Sun Jan 12 2020

Valid 12Z Sun Jan 12 2020 - 12Z Tue Jan 14 2020

  • Heavy snow and significant ice accumulations over parts Northern New England
  • Temperatures will be 15 to 25 degrees above average over much of the Northeast Coast/Mid-Atlantic
  • Heavy snow will blanket the higher elevations of the Northwest...

A powerful winter storm will produce numerous weather hazards to much of
the eastern U.S on Saturday into Sunday will start to wind down.
 The
threat of severe thunderstorms, heavy rain and flash flooding will mainly
end on Sunday.  Upper-level energy will aid in producing 2 to 4 inches of
new snow over parts of the Upper Mississippi Valley/Upper Great Lakes on
Sunday.  Ice accumulations of a quarter to one half inches over Northern
Maine will lead to treacherous travel conditions, power outages, and tree
damage on Sunday.  Gusty winds are anticipated behind the storm which is
why wind advisories are issued across a large portion of the eastern U.S..

 About one and a half inches of rain will continue along the front over
the Southern Mid-Atlantic into parts of the Southeast/Southern
Appalachians into Tuesday morning.

Ahead of this front, much of the Northeast Coast/Mid-Atlantic is getting a
very early glimpse of spring, as temperatures soar into the 60s and 70s.
Numerous daily high and warm overnight low temperature records are
expected to be broken up and down the East Coast on Sunday.  Despite the
storm system's cold frontal passage on Sunday, the colder air behind the
system presently will modify by the time it reaches the East Coast. This
will result in "cooler" temperatures to start the week, but temperatures
will remain 5 to 15 degrees above normal across most eastern regions.

The Pacific Northwest will witness another storm system approach the
region on Sunday, then track into the northern Rockies on Monday. 
Moderate to heavy snow over the Intermountain West and Northern/Central
Rockies will continue through Tuesday.  Snow accumulations will be
measured in the highest peaks of the Cascades, while one to two feet of
snow are likely in the higher elevations of Eastern Oregon, Northern
Idaho, and Central Rockies.  The snow levels will drop down to the coast
Sunday into Monday over parts of Washington State, Oregon, and Northern
California leading to more heavy snow in the Northern Sierra Nevada
Mountains.


Ziegenfelder

 

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---------------------------------------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
113 AM EST Sun Jan 12 2020

Valid 12Z Wed Jan 15 2020 - 12Z Sun Jan 19 2020

Weather Pattern/Hazard Highlights and Guidance/Predictability Assessment...

Mid-upper level troughing over the West will periodically be
reinforced with dynamic eastern Pacific energy, but with a trend
toward less amplified flow through later week. Guidance supports a
deep low off the Pacific Northwest Wed/Thu that would enhance
maritime hazards and inland flow/weather, with energies then
working into the West. Details are less certain for upstream storm
potential, but a favored guidance composite signal is growing for
low development next weekend more off the Pacific
Northwest/western Canada. WPC QPFs and winter weather outlook
probabilities show a widespread snow threat for the Northwest that
reach lower elevations given the extent of cold air filtration.
Activity spreads into CA and the north-central Great Basin/Rockies
mid-late week. Snows over the northern High Plains/Rockies will be
enhanced by post-frontal upslope flow. Activity works back in
ernest into the Northwest next weekend.

Upper trough energies and surface systems will eject northeastward
from the West over the central and eastern U.S. well overtop a
lingering and warming/stabilizing Southeast ridge and interacting
with a lower atmospheric Arctic airmass. A preferred composite
blend of varying GFS/ECMWF and GEFS/ECMWF ensemble guidance
highlights a moderately deepening low threat from the central
Plains to the Northeast Wed/Thu. The blend is now better clustered
with deep cyclogenesis from the Plains to the Midwest/Great lakes
to the Northeast Fri-next Sunday, bolstering forecast confidence
in this potentially significant system. This would favor heavier
rainfall potential later week/next weekend from the south-central
U.S. and mid-lower MS/OH Valleys to southern New England.
The
pattern offers several heavy snow/ice threats in the cooled
northern tier from the Midwest/Great Lakes to the northern
Mid-Atlantic/Northeast as the deepening frontal lows wrap in
deeper moisture as shown by WPC progs, grids, QPFs and winter
weather outlook probabilities.

Schichtel

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
251 AM EST Mon Jan 13 2020

Valid 12Z Mon Jan 13 2020 - 12Z Wed Jan 15 2020

  • Heavy snow to blanket much of the Northwest
  • Areas of showers and thunderstorms to develop over the Southeast and Lower Mississippi Valley
  • Unseasonably mild temperatures to persist across the Eastern U.S., bitterly cold in the Northern Rockies/Plains...

The Northwest will have an active stretch of weather as a pair of storm
systems track through the region over the next couple days and a steady
current of onshore flow will aid in producing the precipitation .  Wintry
weather is the headliner with numerous Winter Storms Warnings and Winter
Weather Advisories in effect from the Cascades of Washington and Oregon,
eastward to the Central Rockies. Snowfall will be measured in feet in the
Cascades, the Northern Sierra Nevada, Northeast Oregon, Northern and
Central Idaho, Western Wyoming, North-Central Utah, and the Colorado
Rockies.
 Winter Storm Watches have also been issued for the Seattle metro
area as they may pickup a few inches of snow.  Expect treacherous and icy
travel conditions in these affected areas.

A frontal boundary will become quasi-stationary from the Mid-Atlantic
Coast stretch southwest across parts of the Tennessee Valley and into the
Western Gulf Coast.  Scattered showers and thunderstorms will form along
the front and could lead to localized areas of flash flooding.  Some
thunderstorms could also be severe over parts of the Tennessee Valley and
Lower Mississippi Valley. 

Unseasonably mild temperatures will continue across the Southeastern U.S.
in wake of the big weekend storm system.  Record warm daily high and low
temperatures will be possible in parts of the Southeast through Wednesday.

 Temperature anomalies on average will range between 10-20 degrees above
normal across much of the Mid-Atlantic/Southeast and into the Central
Appalachians.  Farther west, bitterly cold temperatures will engulf much
of Montana and the Western Dakotas with high temperatures are forecast to
be below zero on Monday and Tuesday.

Ziegenfelder
 

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--------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
156 AM EST Mon Jan 13 2020

Valid 12Z Thu Jan 16 2020 - 12Z Mon Jan 20 2020

  • Significant Late Week Winter Storm Threat from the Upper Midwest to the Northeast

Guidance/Predictability Assessment

The WPC medium range product suite was primarily derived from a
composite blend of the 18 UTC GEFS mean, 12 UTC ECMWF/ECMWF
ensemble mean and the 00 UTC National Blend of Models. This
maintains great WPC continuity. Of the deterministic models, the
12 UTC ECMWF seems to best cluster with GEFS/ECMWF ensembles and
provides a bit more detail consistent with average predictability
and run to run variance. The newer 00 UTC GFS now seems in better
alignment with this WPC blend, but the 00 UTC ECMWF has trended
slightly weaker and a bit slower like recent runs of the UKMET.
They all still have a decent low.

Weather/Hazard Highlights

An organized lead low will support wrap-around heavy snows over
the Northeast Thursday, with lake effect snows in the wake of
system passage as a trailing cold front surges Arctic air/high
pressure southward across much of the central and eastern U.S.

A decent low off the Pacific Northwest Thursday will enhance
maritime hazards as amplified upper troughing/ample height falls
to the south work inland. This will spread a moderate swath of
precipitation across California,the Great Basin/Southwest and
Rockies into Friday. This includes a locally heavy and terrain
enhanced snow threat. Moderate precipitation should also focus
into the Pacific Northwest Friday into the weekend with flow
underneath a less certain/defined series of Northeast Pacific lows.

The upper trough/height falls will progress northeastward over the
north-central and northeast U.S. this weekend overtop a
warming/stabilizing Southeast U.S. upper ridge.
Cyclogenesis/frontogenesis over the Plains Friday will lead to a
risk of weekend deep low track from the Great Lakes/Midwest to the
Northeast/Canadian Maritimes. The lead Arctic airmass will recede
northward with return flow/moisture influx in advance of system
approach, but the stage will be set for a threat of heavy snow/ice
from the Upper Midwest/Great Lakes to the northern
Mid-Atlantic/Northeast. Lake effect snows linger in the wake of
system passage coincident with reinforcing cold air advection.
There is also expectation for a swath of moderate to heavy
frontal/warm sector rains with some runoff issues from the
south-central Plains northeastward toward the Northeast
Friday/Saturday.

Schichtel

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
231 AM EST Tue Jan 14 2020

Valid 12Z Tue Jan 14 2020 - 12Z Thu Jan 16 2020

  • Heavy snow to impact much of the Northwest
  • There is a slight risk of excessive rainfall over parts of Mississippi
  • There will be a mixture of snow and rain/freezing rain over parts of the Upper Midwest to the Northeast
  • Unseasonably mild temperatures to persist across the Eastern U.S. with bitterly cold temperatures across portions of the Northwest and the Northern High Plains

The Northwest will have an active stretch of weather as a pair of storm
moving onshore from the Pacific Ocean and track through the region.  The
fetch of Pacific moisture advancing inland coupled with the presence of
Arctic air filtering south from Southwest Canada will set the stage for
significant winter weather impacts.  Areas of heavy snow can be expected
for the interior of Washington, Oregon, the Northern Great Basin, and the
Central and Northern Rockies going through Thursday.  Winter Storm
Warnings and Winter Weather advisories are in effect across the Pacific
Northwest and the Intermountain West as a result.  Some accumulating snow
will even be possible for the Seattle and Portland metropolitan areas, and
with the cold air in place area wide, expect treacherous and icy travel
conditions.

Meanwhile, a quasi-stationary front situated from the Southern
Mid-Atlantic Coast southwestward down across parts of the Tennessee Valley
and Lower Mississippi Valley is forecast to move very little over the next
couple of days.  The front will be the focus for numerous clusters of
showers and thunderstorms which will be capable of producing heavy
rainfall and some concerns for flash flooding.  In fact, the Weather
Prediction Center has highlighted portions of the Mississippi in a Slight
Risk of excessive rainfall.  Some isolated potential for thunderstorms to
become severe also exists along the front from the Lower Mississippi
Valley and Southeast.

Furthermore, multiple areas of low pressure will track across the Upper
Midwest to the Northeast through Thursday.  Areas of light snow will
develop over the region with an area of rain/freezing rain south,
likewise, from the Midwest into the Northeast

Unseasonably mild temperatures will continue across the South Plain to the
Ohio Valley and Southern Mid-Atlantic.  Record warm daily high and low
temperatures will be possible in parts of the South Plains through the
Southeast.  Temperature anomalies on average will range between 15 to 20
degrees above average across much of the Mid-Atlantic, Southeast,
Appalachians and Tennessee Valley.
 The counter to this very mild weather,
will be some bitterly cold weather across much of Montana, and the Dakotas
where temperatures will be falling well below zero, and with high
temperatures of 30 to 35 degrees below average. 

Ziegenfelder

allfcsts_loop_ndfd2001140427.gif.2037ad52febe9dbecd41eafa438f49ad.gif

-------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1207 AM EST Tue Jan 14 2020

Valid 12Z Fri Jan 17 2020 - 12Z Tue Jan 21 2020

  • Significant Fri-Weekend Winter Storm Threat from the Upper Midwest to the Northeast

...Guidance/Predictability Assessment...

The WPC medium range product suite valid Friday-Sunday was mainly
derived from a composite blend of very well clustered model and
ensemble guidance and the 00 UTC National Blend of Models. This
maintained great WPC continuity in a stormy pattern with above
normal forecast predictability. Increased blend weighting to more
compatible and consistent ensemble means in a more benign pattern
Mon/Tue amid growing forecast spread/uncertainty. 

...Weather/Hazard Highlights...

The track of an amplified upper trough/height falls and frontal
system will spread a moderate swath of terrain enhanced snow
across the Great Basin and Rockies Fri. Upstream Pacific systems
will bring periods of rain/mountain snow to the Northwest, with a
trend for precipitation to shift northwestward and offshore
Sun-next Tue as heights rise.

The aforementioned upper trough will continue to the
east/northeast into the weekend, becoming negatively tilted by the
time it reaches the Northeast. With associated deepening low
pressure slated to track from the High Plains through the Midwest
and then New England and the Canadian Maritimes, the guidance
signal is strengthening for the threat of significant snowfall
from the Upper Midwest into the Northeast with other wintry precip
types also possible to the south of the all-snow area. Some
locations should see wintry precip before a changeover to rain.
Meanwhile locations in the Mid-Mississippi Valley and Lower Ohio
Valley will have to monitor effects from rainfall given the heavy
rain experienced over the past week. Other areas from the
south-central Plains northeastward could see some runoff issues
with locally moderate-heavy warm sector rainfall. Lake effect snow
will linger behind the system in the flow of reinforcing cold air.

Schichtel

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Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Wed Jan 15 2020

Valid 12Z Wed Jan 15 2020 - 12Z Fri Jan 17 2020

  • Heavy snow to continue across the Cascades and starts to wane as heavy snow begins over the Sierra Nevada
  • Rain/Freezing rain to impact the Southern/Central Plains and the Middle Mississippi Valley
  • Above average temperatures continue for the eastern U.S. while bitter cold stretches across the Northern Rockies/Plains and into the Upper Midwest
  • A strong winter storm will develop over parts of the Northern Rockies/Plains on Friday into Saturday

The active pattern over the Pacific Northwest will continue through the
short range as yet another potent low pressure system approaches. 
Favorable upper-level dynamics over the region will continue to produce
heavy snow for the Cascades. 1-2 feet are probable with isolated amounts
higher than 2 feet possible through Friday.
The low pressure system will
arrive Wednesday evening as a plume of moisture moves southward over
Northern California to Southern California by overnight Thursday.  This
combination will produce up to another foot over parts of the Pacific
Northwest mountains while about 2 feet of snow will fall across parts of
the Sierra Nevada Mountains on Thursday starting to wane on Friday.

Furthermore, weaker upper-level energy and moisture moving northward over
the Plains will aid in producing rain, snow, and rain/freezing rain over
parts of the Southern Rockies/Southern Plains on Thursday expanding into
parts of the Middle Mississippi Valley on Thursday night into Friday.  The
wintry mix will produce hazardous travel conditions.

Meanwhile, upper-level energy over the Northern Rockies/Plains will spawn
a new low pressure system over the Middle Mississippi Valley.  This low
will go on to produce snow, rain and freezing rain for much of the Upper
Mississippi Valley/Great Lakes and moving into the Northeast on Thursday. 
2-6 inches of snow is likely for the Upper Mississippi Valley/Great Lakes
with an isolated area of 8 inches possible for a portion of the Upper
Peninsula of Michigan.  Snow will ramp up over Northern New England as the
low strengthens while moving out to sea Thursday night producing 6-8
inches of snow.

A Marginal Risk of Excessive Rainfall leading to isolated flash flooding
is in effect for parts of the Lower Mississippi Valley into Southern
Appalachians due to the presence of a stationary boundary oriented
diagonally across the Southeast. Isolated areas of over an inch possible
for these areas.
 In addition, a Marginal Risk of Excessive Rainfall will
also lead to isolated flash flooding over parts of Northern California and
Southern Oregon. 

Below average temperatures will develop over Northern Montana. 
Nonetheless, air temperatures will be between 20-40 degrees below normal
through Thursday.  Conversely temperatures will be between 10-25 degrees
above average on Wednesday.
 Temperatures will begin to moderate on
Thursday.

Ziegenfelder

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-------------------------------------------------

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
137 AM EST Wed Jan 15 2020

Valid 12Z Sat Jan 18 2020 - 12Z Wed Jan 22 2020

  • Significant Weekend Winter Storm Threat from the Upper Midwest to the Northeast

...Guidance/Predictability Assessment...

A dynamic upper trough tracking from the Plains to the Northeast
will spawn a significant weekend low from the Midwest to New
England.
Models and ensembles show solid agreement with the storm
and a composite blend coupled with the National Blend of Models
seems to offer a very reasonable forecast in a pattern with above
normal predictability/continuity.

By early-mid next week, forecast spread increases in a generally
more benign weather pattern over the nation. Given this spread,
the WPC forecast blend trended to the more compatible and
consistent GEFS/NAEFS/ECMWF ensemble means. This maintains good
continuity.


...Weather/Hazard Highlights...

The guidance signal remains strong for a significant weekend
snowfall from the Upper Midwest/Great Lakes to the Northeast, with
a combination snow/sleet/freezing rain also possible to the south
of the all-snow area. A progressive swath of frontal/warm sector
rains/convection are likely into Saturday from the lower MS Valley
northeastward to the East, where dammed cold air retreats
northward ahead of the low in a potentially messy transition.
Lake
effect snow will linger behind the low in the reinforcing cold air
flow.

Upstream, the inland approach of northeast Pacific upper troughing
should be shielded by a warming/stabilizing upper ridge building
over the West. This may mainly limit periods of precipitation to
the Pacific Northwest. Downstream, uncertain trough energies will
dig to the lee of the upper ridge into the cooled east-central
states. Moisture will be limited in the wake of the lead storm,
but expect lingering lake effect snows and some potential to
induce western Atlantic frontal waves given sufficient upper
trough amplification.

Schichtel

Links

hazards_d3_7_contours200115.thumb.png.a14651f877693c9b2ac5a37ec597b38f.png

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