Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
308 PM EDT Sun Mar 20 2022
Valid 12Z Wed Mar 23 2022 - 12Z Sun Mar 27 2022
...A low pressure system will likley spread moderate to heavy rain
through the eastern U.S. midweek, with severe storms possible in
the Southeast, and wintry weather across the northern tier...
...Overview...
Active weather will likely reach the eastern U.S. by Wednesday
with a tendency of decreasing rain intensity as a large occluded
cyclone should gradually weaken and move across the region late
this week, with initial threat of severe thunderstorms ahead of
the cold front in the Southeast. Meanwhile on the cold northern
side of the system, springtime snow and mixed precipitation are
possible from the Great Lakes region to the interior Northeast.
As a ridge builds into the West, possible record high temperatures
across California will be contrasted with a cooling trend in the
Great Lakes to the Northeast where an upper trough is forecast to
amplify. This increase in amplitude of the upper-level pattern
across the U.S. by next weekend would introduce higher uncertainty
and thus lower predictability particularly across the Northeast
and just off the West Coast.
...Guidance Evaluation/Predictability Assessment...
The medium-range period will begin on Wednesday as an occluded
cyclone will likely be near peak intensity as the cyclone center
tracks across the Midwest. Model guidance/consensus continues
with a subtle trend of wrapping additional precipitation around
the northern side of the cyclone across the upper Midwest toward
the northern Plains, while rain and thunderstorms ahead of the
trailing cold front were nudged progressively faster through the
eastern U.S. This trend is due to a gradual amplification of the
upper trough behind the cyclone across the Plains states in the
model guidance, leading to a gradual trend for the cyclone to
evolve into a classical occlusion. The CMC remains to be the more
enthusiastic guidance in this regard, though with noticeable
run-to-run variability, and thus has been the slowest guidance in
pulling the system out of the Northwest late this week. The GFS
and ECMWF are mostly in agreement with one another, and not as
slow as the CMC regarding this system.
Toward next weekend, models are generally indicating a trend
toward an increasingly amplified pattern across the U.S. as a
ridge is forecast to build over the West while upper-level
shortwaves are predicted to dig southeastward from central Canada
toward the northeastern U.S. This increase in amplitude of the
upper-level pattern would tend to introduce higher uncertainty and
thus lower predictability particularly across the Northeast and
just off the West Coast where another amplified trough in the
Pacific appears to edge closer. Both the EC and GFS begin to
diverge from their corresponding ensemble means by late week,
which implies higher uncertainty with the pattern.
Therefore, the WPC medium-range packaged was based mainly on the
consensus of the 00Z ECMWF/EC mean and the 06Z GFS/GEFS mean, with
increasing usage of the ensemble means toward the weekend. A
small contribution of the 00Z CMC was included for Days 3-4
followed by a small amount from the CMC mean Days 5-7. The
results are reasonably compatible with WPC continuity.
...Weather Highlights/Threats...
Another rainy day is expected as the medium range period begins
Wednesday as Gulf of Mexico moisture ahead of the low pressure
system tracking across the central U.S. will likely begin trending
downward thereafter. Storms could be severe across the Deep South
down to the central/eastern Gulf Coast per the Storm Prediction
Center. Furthermore, widespread rain is likely across the East,
which could potentially cause some isolated flash flooding in some
areas from the southern/central Appalachians eastward. North and
west of the low track, snow and wintry precipitation are possible,
with the highest probabilities for notable snow in the Upper Great
Lakes region. Wintry mix or snow could also occur particularly in
higher elevations of the interior Northeast north of a warm front
on Wednesday-Thursday and as a western Atlantic low develops by
early Friday. Showers could linger into late week across the East
with generally light amounts expected, but perhaps with more
moderate amounts as a front lingers in Florida, which could cause
localized flooding issues if rain falls atop saturated soils. A
mainly dry pattern is expected for the western and central U.S.
for the latter part of the week, though with some Pacific
Northwest and Northern Rockies light precipitation possible before
a more widespread moisture surge next weekend.
The strong upper ridge building into the West will lead to a broad
area of highs 10-20F above normal Wednesday-Sunday with slightly
higher localized anomalies possible. There is potential to reach
daily record highs across California Wednesday to Friday and
spreading eastward into the Intermountain West and Southwest as
the ridge axis shifts east. Leading upper level troughing should
support temperatures 10-20F below average across the
central/southern High Plains Wednesday. The cooler air should
moderate closer to normal by the latter part of next week as it
progresses eastward. Ahead of the trough and cold fronts,
generally warmer than normal conditions are likely across much of
the eastern third of the U.S. for much of the week, transitioning
to near normal temperatures by Friday and Saturday and a cooldown
associated with a secondary cold front in the Great Lakes by
Sunday. Isolated record highs are possible over parts of Florida
Tuesday-Wednesday.
Kong/Tate
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
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