Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
156 AM EST Tue Nov 30 2021
Valid 12Z Fri Dec 3 2021 - 12Z Tue Dec 7 2021
...Overview...
A quasi-zonal flow pattern is expected to be in place to close out
the work week across the northern tier states with a pronounced
trough exiting the East Coast. By the weekend, an upper ridge
axis tries to become established over the West Coast and the
eastern Pacific, and a trough amplifies with developing surface
low over the Plains. This will likely be followed by a second
well organized storm system by the end of the forecast period
across the western High Plains, with a zonal flow pattern across
the eastern half of the nation.
...Guidance/Predictability Assessment...
The 00Z model guidance suite is in decent agreement on Friday
before more noticeable differences emerge by Saturday, with the
GFS indicating a flatter trough over the Great Lakes and
Northeast, and the ensemble means are not capturing the magnitude
of the incoming trough across the Pacific Northwest that will
eventually lead to an organized low pressure system over the
Plains by Sunday morning. The CMC has trended more in line with
the model consensus compared to previous days across the western
U.S., and is reasonably close to the GFS and ECMWF with portraying
the next trough/storm system arriving on the West Coast by Monday
night. By the end of the forecast period, the GFS is considerably
stronger and slower with the trough approaching the East Coast.
The WPC forecast was primarily based on a CMC/ECMWF/GFS blend
through Saturday. Thereafter, increased weighting towards the
ensemble means whilst keeping some of the operational GFS and
ECMWF.
...Weather/Hazards Highlights...
Weather should be relatively uneventful in terms of rainfall or
snow related hazards with not much in the way of heavy
precipitation currently expected through early Sunday. Rounds of
relatively light precipitation are forecast for the Midwest, Great
Lakes, and Northeast with a progressive storm track over the
region. Moisture increasing ahead of a cold front is expected to
result in scattered showers and a few thunderstorms from the Deep
South to the Ohio Valley over the weekend, but amounts are not
currently expected to be excessive. A shortwave and cold front
reaching the Pacific Northwest by Sunday night and through Monday
is expected to result in another round of moderate to locally
heavy rain and mountain snows to western Washington and Oregon,
with some of this moisture reaching the northern Rockies by
Tuesday with heavy snow possible for the higher elevations of
northern Idaho, western Montana, and western Wyoming.
Temperatures are expected to be above normal for early December
across most of the nation through early next week, with the
greatest positive anomalies expected for the central and southern
Plains on Friday where highs are forecast to be 15 to 25 degrees
above average. Another episode of well above normal temperatures
is likely for the western High Plains on Monday ahead of the next
cold front. A few locations may approach daily record highs with
these mild temperatures. On the other end of the spectrum, cold
weather is forecast to continue across the Northeast U.S. with
highs running up to 10 degrees below normal through the weekend
with a cold upper level trough overhead. However, no major arctic
airmass intrusions are expected during this forecast period.
Hamrick
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook 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