Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
153 AM EST Fri Feb 19 2021
Valid 12Z Mon Feb 22 2021 - 12Z Fri Feb 26 2021
...Overview and Guidance Evaluation...
A relatively progressive upper flow pattern will be in place for
the beginning of the week as the eastern U.S. trough departs.
This will be followed by zonal flow across much of the central and
eastern U.S. ahead of an amplifying western U.S. trough by
Wednesday. A second trough will likely follow for the Pacific
Northwest by the end of the week.
The 00Z model guidance suite is overall in above average agreement
on the synoptic scale pattern through Tuesday. By Wednesday and
beyond, the CMC becomes a little more amplified with the western
U.S. trough and is slower to lift it out by the end of the
forecast period, and the 00Z GFS parallel is quite strong with the
second trough/closed low approaching the Pacific Northwest by
Thursday, but is competitive elsewhere across the continental U.S.
For the fronts and pressures forecast, the 18Z GFS parallel was
preferred over the operational 18Z GFS given some timing
differences with the pattern change across the West, with the
parallel version closer in line with the model consensus. A blend
of the 12Z ECMWF/18Z parallel GFS/12Z CMC was used through early
Wednesday, and then discontinued CMC by Thursday and Friday and
more weighting towards the EC and GEFS means.
...Weather/Threats Highlights...
Things will be relatively uneventful across most regions of the
nation compared to the extreme winter weather that has been
endured by many locations this past week. A departing storm
system across the East Coast region early in the week is expected
to produce mainly light to moderate rainfall, and some snow from
the northern Mid-Atlantic to New England. The heaviest snow
should be confined to portions of upstate New York that get lake
effect snow in the wake of the departing low. A stronger storm
system crossing the Pacific Northwest and the Rockies is expected
to produce heavy snow for the higher terrain of the Cascades, and
extending across northern Idaho, western Montana, western Wyoming,
and then central Colorado by the middle of the week, and will
likely affect much of the Interstate 25 corridor.
In the temperature department, the building trough and the passage
of the cold front across the Intermountain West will herald a
change to readings falling to 10-20 degrees below average for the
western High Plains to the Rockies, along not nearly as impressive
as the recent Arctic blast based on our current forecasts.
Temperatures will likely be 10-20 degrees above average ahead of
that same storm system across the northern Plains.
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