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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2105Z Dec 06, 2019)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
405 PM EST Fri Dec 06 2019

Valid 12Z Mon Dec 09 2019 - 12Z Fri Dec 13 2019

...Heavy rain potential for Mid-South to Northeast early next
week...
...Well below normal temperatures over the northern Plains/Upper
Midwest early-mid week...


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

A deep vortex that dips south to Hudson Bay this weekend remains
centered there through next week. A notable trough rounding this
low amplifies across the eastern 2/3 of the CONUS by Tuesday with
lesser troughing/cyclonic flow through the rest of week. An
upstream ridge amplifies up the North American West Coast early in
the week before being weakened through the midweek by shortwave
activity off a Gulf of Alaska low. The southern stream flow
associated with the amplifying trough early in the week has
uncertainty in terms of magnitude and ejection timing across the
southern CONUS Tuesday through Thursday.

A multi-model deterministic blend works generally well through Day
4/Tuesday with the progression of the positively tilted trough
pushing southeast across the western CONUS as the trough
amplifies. The 00Z CMC/UKMET are then slower/stronger with the
southern stream trough over Texas than the 00Z ECMWF/06Z GFS which
is preferred for Day 5/Wednesday. A blend of the 00Z ECENS/06Z
GEFS was then favored for Day 6/7 with an understanding that
shortwave features crossing the southern/central CONUS will
determine the sensible weather, but are washed out by blending the
means.

This Hudson Bay gyre looks to persist through the middle of the
month. The next lobe may be with interaction from eastern Pacific
impulse energy/moisture rounding the western ridge which may allow
another trough to amplify over the eastern CONUS next weekend.


...Weather Highlights/Threats...

There is a strong signal for heavy rainfall to continue ahead of
the main cold front with this amplifying trough Monday night from
the lower MS Valley to the northern Mid-Atlantic and
southern/eastern New England. Locally heavy snow may persist in
the comma head of the parent low over the central Great Lakes at
this time as well. Lake effect snow should spread across the Great
Lakes into Tuesday in the wake of the cold front which is
particularly cold. Polar plunges are expected behind the cold
front with temperature anomalies of 15 to 30 degrees below normal
centered over the Upper Midwest with reinforcing shots of cold
air.

Jackson


Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

Hazards:
- Heavy precipitation across portions of the Pacific Northwest and
the Northern Great Basin, Wed-Fri, Dec 11-Dec 13.
- Heavy rain across portions of northwestern Washington, Wed-Thu,
Dec 11-Dec 12.
- Heavy rain from the upper Texas coast to central Louisiana, Fri,
Dec 13.
- Heavy rain from the northern Mid-Atlantic through the eastern
half of New England, and from the Tennessee Valley and the
southern Appalachians up along the western slopes of the central
Appalachians, Mon-Tue, Dec 9-Dec 10.
- Heavy snow across portions of the northern Rockies and the
northern Intermountain region, Thu-Fri, Dec 12-Dec 13.
- Heavy snow from northern Wisconsin eastward into the central
Great Lakes, Mon, Dec 9; and for the central Great Lakes, Wed, Dec
11.
- Flooding occurring or imminent across portions of the Northern
Plains.
- Much below normal temperatures across portions of the Great
Lakes, the upper Midwest, and much of the northern Plains,
Mon-Wed, Dec 9-Dec 11.
- Much below normal temperatures for northern New England,
Wed-Thu, Dec 11-Dec 12.


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

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml