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Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 0700Z Dec 07, 2019)
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EST Sat Dec 07 2019

Valid 12Z Tue Dec 10 2019 - 12Z Sat Dec 14 2019

...Much below normal temperatures for the Northern
Plains/Midwest/Great Lakes...

...Pattern Overview and Guidance/Predictability Assessment...

A southern stream flow associated with an amplifying Southwest
upper trough early week still offers some uncertainty in terms of
magnitude and ejection timing for the U.S. southern tier Tuesday
into Thursday, but guidance clustering has improved to bolster
forecast confidence.

Overtop, a cold Hudson Bay upper vortex lingers next week. A
notable upper trough rounding underneath amplifies to the central
then eastern lower 48 states Tuesday/Wednesday, with less
amplified troughing/cyclonic flow for much of the rest of week. An
upstream ridge amplifies up the North American West Coast early
week before being weakening midweek by eastern Pacific shortwaves
that cut inland from the Northwest to the snowy Rockies.

A favored and reasonably well clustered GFS/ECMWF and GEFS/ECMWF
ensemble solution suggests  this energy may subsequently renew
central to southern/eastern U.S. upper trough amplification where
their is a threat of cyclogenesis and lower atmospheric cold air
damming to keep an eye on heading into next weekend.  

...Weather Highlights/Threats...

There remains a strong signal for a swath of moderate rainfall
ahead of a main cold front from the lower MS Valley to the
Appalachians/Mid-Atlantic and southern/eastern New England
Tuesday. Activity will shift offshore midweek. Frontal waves and a
dynamic upper trough/jet also supports some enhanced snows on the
cooled northwest periphery of the precipitation shield from
Appalachians to the Northeast. Lake effect snow should also perist
across the Great Lakes in the wake of the cold front which is
particularly cold. Polar plunges are expected behind the cold
front offer temperature anomalies of 15 to 30 degrees below normal
centered over the Upper Midwest with reinforcing shots of cold

Over the West...a building West Coast upper ridge should keep most
of the West dry through early next week beyond some Rockies snows.
The pattern should become more wet and elevation snowy for
especially the Pacific Northwest, but also inland to the Rockies
as shortwave energies round the northern part of the ridge later


Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at: