Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Sun Mar 07 2021
Valid 12Z Wed Mar 10 2021 - 12Z Sun Mar 14 2021
...Late-week heavy rain possible from the central Plains to the
Mid-Mississippi Valley/Midwest...
...Overview and Guidance/Predictability Assessment...
Models and ensembles continue to indicate that an amplified
southern stream upper trough/low will settle over the
West/Southwest this week in a pattern with above normal forecast
predictability. This trough will support rain and higher elevation
snow along with the advent of below normal temperatures. Lead
energies forecast to eject from the trough will support a quite
wavy and slow-moving central to eastern U.S. front whose Gulf
moisture and instability pooling will fuel a focus for locally
enhanced rainfall and training convection.
Ahead of this evolution, eastern U.S. heights will tend to rise
for much of the coming workweek as ridging moves in from the
central U.S. and the Gulf of Mexico. This will bring much above
normal temperatures from the north-central U.S. to the East.
Toward the end of the week and next weekend, models generally
agree that a cold front will progressively move through the
Midwest and down through the East in response to amplified
northern stream upper trough passage whereas the trailing front
will become nearly stationary from the central/southern Plains to
the Mid-Mississippi and into the Ohio Valley, where there is ample
model signal for an axis of heavy rain to develop. Low pressure
waves that form and track along the front would be instrumental in
producing periodic heavy rains. However, the timing of the waves
will be difficult to resolve until we get closer to the event. By
next weekend, model solutions begin to diverge across the
mid-section of the country as the GFS/GEFS brings the western U.S.
trough noticeably faster into the Plains than the ECMWF solutions,
whereas the CMC/CMC mean offers a faster version of the ECMWF
solutions.
The WPC medium range product suite for Days 3-5 was derived from a
composite blend of the 06Z GFS/GEFS mean, the 00Z ECMWF/EC
ensemble mean, smaller contributions from the 00Z CMC/CMC mean, as
well as the 13Z National Blend of Models. For Days 6-7 (next
weekend), an intermediate solution based mainly on a blend of the
ensemble means with little or no contribution from the
deterministic GFS was adopted. WPC continuity is well maintained
with this forecast strategy.
...Weather/Threats Highlights...
Expect rain/higher elevation snow as an upper trough/low settles
into the West/Southwest in separated southern stream flow.
Heavier precipitation will focus over favored terrain in
California, with highest amounts lingering into this period for
the Sierra Nevada and coastal ranges. Some meaningful
precipitation will also spread across the Interior West and
Rockies with the upper trough/low, ejecting impulses and frontal
system progressions. Energies ejecting into the Plains will
support frontal low pressure systems with enhanced precipitation
focusing into the south-central Plains, Mid-Mississippi Valley,
and Midwest/Great Lakes/Ohio Valley with the return and pooling of
Gulf moisture and instability. Some wintry weather may be
possible over northern locations. Activity will focus near a wavy
trailing cold front that will tend to stall as upper troughing
settles over the West, possibly leading to cell training. There
is increased forecast spread with respect to the eventual ejection
and increasingly neutral tilt of the main Southwest upper trough
next weekend, but height falls and instability may invigorate
precipitation potential for the south-central Rockies/Plains with
deformation and terrain/upslope flow. This includes a wintry
threat focus from the Rockies to the High Plains as lead cold air
filters southward through the central and eastern U.S. By next
weekend, the lingering front across the Deep South should continue
to keep a good chance of precipitation in the vicinity while the
Southwest should enter a drying trend as the upper trough should
progress further east toward/into the southern Plains.
Temperature-wise, anomalous warmth across the northern Plains is
forecast to spread southeastward through the East Coast bringing
the first sign of spring into the area. In contrast, cooler than
normal conditions will continue for much of the West before a
gradual warming trend sets in later this week from the Pacific
Northwest to the northern Plains.
Kong/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