Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM 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...
The pattern aloft by early-mid next week will highlight a closed
vortex over Hudson Bay as troughing/cyclonic flow rotates
underneath from a chilled and unsettled north-central to
northeastern U.S. This is supported by an amplified upstream ridge
aloft on the North American West Coast. A southern stream flow
meanwhile features shortwave trough ejection from the Southwest
Monday to the Southern Plains Tuesday that then phases with a more
dominant northern stream. Recent GFS/ECMWF runs are trending to a
compromise amplitude and progression solution that is becoming
increasingly consistent with their latest ensembles.
A composite 00 UTC model/ensemble solution still also suggests
that gradual rounding of the West Coast ridge later next week
would let increased eastern Pacific impulse energy/moisture work
inland from the Northwest/Rockies to the Plains. This may also set
the tone for robust east-central U.S. upper trough amplification
to keep an eye on heading into next weekend.
...Weather Highlights/Threats...
Over the West...a building West Coast upper ridge should keep most
of the West dry through early next week beyond some lingering
Rockies snows in northwest flow. 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 mid-later week.
There is a strong signal for heavy rainfall over a broad area from
the Mid-South to the northern Mid-Atlantic and southern/eastern
New England Monday/Monday night with frontal approach and support
aloft. Locally heavy snow is possible in the comma head of this
low over the Upper Midwest Sunday night through Monday with
potential Lake Superior enhancement. Lake effect snow should
spread across the remainder of the Great Lakes Monday into Tuesday
in the wake of the low which is particularly cold. Polar plunges
are expected behind the cold front with temperature anomalies of
15 to 25 degrees below normal centered over the Upper Midwest with
reinforcing shots of cold air.
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