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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0714Z Dec 08, 2019)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
214 AM EST Sun Dec 08 2019

Valid 12Z Wed Dec 11 2019 - 12Z Sun Dec 15 2019

...Much below normal temperatures linger for the Upper
Midwest/Great Lakes Midweek...
...Emerging wet flow over the Northwest...
...Cold air damming lends a wintery risk over the East with
potential low developments... 

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

A cold Hudson Bay upper vortex lingers next week. A notable upper
trough rounding underneath shifts over the Midwest/Great Lakes
midweek then ejects over the Northwest, with less amplified but
still active troughing/cyclonic flow for much of the rest of week
over the lower 48. This occurs as an early week North American
West Coast ridge is rounded by eastern Pacific shortwaves that cut
inland from the Northwest to the north-central Great
Basin/Rockies. This is also as an active southern stream provides
multiple trough energy passages underneath over the U.S. southern
tier to further focus inflow/activity, culminating with potential
QPF/wintery enhancement later week from the Southeast to up the
Eastern Seaboard. 

The WPC medium range product suite was primarily derived from a
composite blend of the GFS/ECMWF and GEFS/ECMWF ensemble means,
lending increasing weighting in this blend from the determinitsic
models to ensembles through the period amid growing forecast
spread over time.


...Weather Highlights/Threats...

Great Lakes effect snows will persist midweek. Temperature
anomalies of 15 to 30 degrees below normal will be over the Upper
Midwest and Upper Lakes with reinforcing Arctic shots.

Out West, the pattern should become quite wet across the Pacific
Northwest by mid-later this week as Pacific shortwave energies
punch through rounding West Coast flow. Dynamic support for
activity will extend inland with impulse progressions, with
moderate to heavier snows to continue on favored terrain of the
north central Great Basin/Rockies into next weekend.

Models continue to show support for the development of a
significant waves of low pressure along a surface front in the
Gulf of Mexico by late next week, tracking northeastward across
the Southeast U.S. and up the Eastern Seaboard into next weekend.
Spread is considerable with the timing and the eventual tracks of
these features, but the pattern seems to favor organized
cyclogenesis to focus moisture and lift to produce a risk of heavy
rainfall across the Southeast. Subsequent system deepening,
northward lifting, and interaction with a slow to recede lower
atmospheric cold air damming over the East may offer an emerging
snow/ice threat to monitor.

Schichtel

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

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