Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Wed Feb 24 2021

Valid 12Z Wed Feb 24 2021 - 12Z Fri Feb 26 2021

...Relative quiet across lower 48 to proceed an active end of the week for
the Deep South...

...A mild Wednesday in the East as colder temperatures return to the
Rockies and Central/Southern Plains...

...Avalanche Warnings in the Northern Rockies...

A low pressure system will glide across the Northeast today before
departing into the Canadian Maritime on Thursday. As a result, a swath of
light snow is expected to stretch from parts of the Upper Great lakes to
the Northern Appalachians. The southern portion of this frontal system
will eventually settle across the southern tier of the CONUS by Thursday.
Areas of moderate snow may develop over parts of central Colorado
Wednesday night as the tail end of the aforementioned frontal boundary
descends through the area. An area of low pressure will develop along this
stationary front and contribute to the potential for moderate rainfall and
thunderstorms across an aerial swath extending from eastern Texas to
northern Mississippi Thursday night into Friday.

Meanwhile, another low pressure system will bring heavy snow to the
mountains of the Northwest on Thursday and Friday. Parts of the Cascades
(particularly northern portions) will see multiple feet of new snow, while
the Northern Rockies will see up to a foot of snow with locally higher
amounts possible, especially over the highest peaks. Avalanche Warnings
are in effect for parts of the Northern Rockies (northern Idaho/Montana)
where prolonged snowfall is especially likely.

The eastern U.S. will experience a warm up today before the cold front
sweeps through the region tomorrow. Highs maybe between 15-20 degrees
above average for parts of the Mid-Atlantic and Tennessee Valley.
Meanwhile, temperatures are expected to drop across the Rockies and the
Central/Southern Plains as the tail end of the east coast system sweeps
through Texas and the Southwest today. The arrival of high pressure over
the Rockies on Thursday will contribute to the anomalously cold air mass
that will settle over parts of eastern New Mexico, southeastern Colorado
and the Texas Panhandle, where highs maybe between 20-30 degrees below
average.

Kebede
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
Wed Feb 24 2021

Valid 12Z Sat Feb 27 2021 - 12Z Wed Mar 03 2021

...Potential heavy rainfall from the southern Plains to the
Tennessee Valley this weekend into early next week...

...Overview and Guidance Evaluation...

Quasi-southwesterly flow aloft is expected over the CONUS during
the period with a couple Pacific systems dropping into the Four
Corners region while a deepening trough quickly moves through the
northern stream. Ridging is expected to persist over southern
Florida and parts of the Gulf of Mexico and the resulting
southwesterly flow will allow Gulf moisture to lift into parts of
the CONUS. This moisture and associated boundary will be
interacting with high pressure form the north, creating a zone for
some episodes of heavy rainfall this weekend into early next week
across portions of the Southern Plains to southern Appalachians.

Through day 5, the models show fairly good agreement with the
Pacific system dropping down to the Four Corners then pushing out
into the Plains by early day 6. In the northern stream, the models
continue to advertise a deeper solution with the upper level
trough, giving way to a stronger low passing through day 3-4-5. In
its wake, stronger high pressure is now forecast to drop down into
the Plains. This effectively pushes the wavy stationary boundary
across the South further south by day 5/6. Meanwhile, there is
much uncertainty with the day 6/7 Pacific/West Coast trough.
Although many of the models now show a deeper low pinching off
well offshore.

The GFS appeared to be again too strong with the northern stream
energy, though the trend is for a more pronounced trough taking on
a negative tilt, so it was not entirely discarded. Elsewhere
through day 5, a blend of the available deterministic guidance
sufficed. By day 6/7, the forecast confidence was below normal
regarding the position of the stationary boundary/front across the
South - the models now suggest a stronger high to the north which
could push it toward the Gulf Coast (and push heavy rainfall
threat to the south as well). Meanwhile, the west coast trough
evolution is very uncertain, so a blend heavy on the ensemble
means was used.

The WPC blend was derived based on the consensus of the 12Z
ECMWF/12Z EC mean, the 18Z GFS/18Z GEFS, and smaller contribution
from the 12Z CMC, and mostly a blend of the ensemble means on day
6-7 to account for the forecast uncertainty.

...Weather/Threats Highlights...

Precipitation spreading into portions of the central to northern
Rockies could result in heavy snow for the higher elevations.
Meanwhile, upper level troughing over the Four Corners region will
allow Gulf moisture to lift northward as waves of low pressure
move along a stationary boundary in place. This setup will favor a
few rounds of locally heavy rainfall this weekend into early next
week across portions of the Arklatex to the TN and OH Valleys. The
latest guidance shows the possibility of general rainfall totaling
several inches over the period.

Farther north, some wintry precipitation can be expected across
the central Appalachians Friday night into early Saturday, across
the upper Great Lakes early on Saturday, across the Midwest on
Sunday and Sunday night, and across northern New England Monday
and Monday night. Another round of wintry weather is possible
across the Midwest on Monday.

Below normal temperatures are expected to remain primarily over
the Northern Rockies to start the period with departures of 10F to
as much as 20F Saturday while the eastern half of the CONUS
experiences slightly above normal daytime highs. Ahead of the
stationary boundary expected to be draped across portions of the
South, daytime highs as much as 15F above normal are possible
Sunday along the Gulf Coast as well as portions of the Northeast
and New England. Nighttime lows are forecast to be well above
normal (10 to 20F) for much of the central and eastern U.S. Sunday
and Monday, ahead of the frontal boundary draped through the MS
River Valley to Great Lakes.

Taylor