Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
156 AM EST Sun Feb 21 2021
Valid 12Z Wed Feb 24 2021 - 12Z Sun Feb 28 2021
...Overview and Guidance Evaluation...
The medium range period is forecast to begin on Wednesday with
generally zonal upper-level flow, with a noticeable separation of
northern and southern stream flow for the middle of the week. The
flow pattern should be relatively progressive through the week, as
the Northwest trough deepens and tracks eastward, and then
additional troughing and energy come into the West for the latter
part of the week and becomes a broader synoptic scale trough over
the western U.S. by next weekend.
Model guidance is in generally good agreement with the synoptic
scale pattern through the first half of the medium range period.
The 12Z CMC was nearly completely out of phase with the model
consensus across the western Pacific for next weekend, but the new
00Z run appears more reasonable. Similar to yesterday, the GFS
parallel is slightly slower with most shortwave features compared
to the more progressive operational GFS, and the parallel version
was favored more for the WPC fronts and pressures. The 12Z ECMWF
was also incorporated along with gradually increasing
contributions from the EC and GEFS mean.
...Weather/Threats Highlights...
The West could be moderately active in terms of precipitation
through early Saturday, with heavy snow possible for higher
elevations of the Cascades and the northern Rockies. There will
likely be a round of moderate snow for the Colorado Rockies and
Front Range on Wednesday along and west of the Interstate 25
corridor. By next weekend, a southern stream disturbance may tap
enough Gulf of Mexico moisture to produce a swath of moderate
rainfall across portions of the Mid-South and potentially some
light wintry precipitation across portions of the Midwest.
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. Ahead of the front,
temperatures will likely be about 5 to 10 degrees above average
across the East Coast region for midweek. By the end of the
forecast period next weekend, expect temperatures to be near to
slightly below normal for most of the nation.
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