Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
150 PM EST Sun Feb 20 2022
Valid 12Z Wed Feb 23 2022 - 12Z Sun Feb 27 2022
...Heavy to excessive rainfall threat from the Lower
Mississippi/Tennessee Valleys to the Mid-Atlantic along with a
heavy snow/ice threat from the southern Plains to the Northeast
Wednesday-Friday...
...Pattern Overview...
Expect an active mid-winter pattern this week as cold Canadian
high pressure digs across much of the lower 48 states. Upper level
troughs will dig through the West, with ejecting energies and
induced frontal waves progressing downstream then overtop a
warming Southeast/East upper ridge. The main upper trough should
shift eastward into the Central Plains and Midwest by later week
as amplified ridging builds from the East Pacific into the West
Coast. This amplified pattern favors a heavy to excessive rainfall
threat from the Lower Mississippi/Tennessee Valleys to the
Mid-Atlantic along with a heavy snow and ice threat from the
southern Plains to the Northeast Wednesday into Friday.
...Guidance Evaluation/Predictability Assessment...
The latest suite of models and ensembles continue to offer a
similar large scale flow evolution through at least day 5. As
such, a composite blend of the 06z GFS and 00z ECMWF/UKMET/CMC
were used. After day 5/next weekend, there remains questions on
how quickly the pattern will deamplify and the upper trough energy
weakens and shifts east. The 00z ECMWF is notably stronger with
this energy and slower, with the 06z/12z GFS trending much faster.
The 00z/12z CMC actually provides a decent middle ground solution,
along with the ensemble means. These differences contribute to
frontal placement uncertainties across the South on day 7 and some
rather significant QPF differences too. For days 6-7, prefer a
solution more amplified than the GFS, but maybe not quite as
robust as the ECMWF. The WPC blend used smaller portions of the
CMC/ECMWF blended with the enesmble means, which also kept good
continuity with the previous WPC forecast.
...Weather Highlights/Threats...
Moderate to heavy mountain snows are likely midweek for the
south-central Great Basin/Rockies with the approach/passage of
potent upper trough energy and as enhanced by upslope fetch. Ample
upper energies working downstream from the West will also act to
induce waves along a lead front and tap deepening moisture from
the Gulf of Mexico. This is expected to fuel a heavy to excessive
rainfall and convection threat from the Lower
Mississippi/Tennessee Valleys to the Mid-Atlantic, mainly
Wednesday/Thursday. Some parts of especially the Tennessee Valley
may receive additional heavy rainfall during this time, after an
initial round in the short range period, which could lead to an
increased threat for flooding and/or flash flooding. Wave
organization and redevelopment should also support the spread of a
potentially significant heavy snow/ice threat from parts of the
southern plains and Mid-Mississippi/Ohio Valleys to a cold air
dammed northern Mid-Atlantic and Northeast Wednesday-Friday.
Strong ridging building over the Western U.S. mid to late period
should result in a very dry period across much of the West, though
some rain/mountain snow may try to move back into the Pacific
northwest next weekend associated with northeast Pacific shortwave
energy. Across the South, significant uncertainty concerning
amplitude/speed of the Western trough results in large differences
in potential QPF across the mid-south, especially the lower
Mississippi Valley to Tennessee Valley. Generally light to
moderate return flow moisture into the region is expected,
although there are some model solutions suggesting a heavier event
could materialize resulting in another round of heavy rainfall for
an already water logged region.
The cold high pressure surge will spread much below temperatures
across much of the western and central U.S. by mid-late week to
include widespread record cold values, especially frigid from the
northern High Plains to the Northern/Central Plains where daytime
highs and overnight lows could be 30-40+ degrees below normal.
This very cold air will spread, but gradually modify later week
across the Midwest/East. Meanwhile, much above normal pre-frontal
temperatures are expected across the Southeast/East with some
record warmth likely, especially overnight mins with upper level
ridging and enhanced pre-frontal moisture into the region.
Santorelli/Schichtel
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