Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
221 AM EDT Thu Mar 25 2021
Valid 12Z Sun Mar 28 2021 - 12Z Thu Apr 01 2021
...Overview...
The upper level pattern during the medium range period should be
pretty progressive with two main systems of note. The first, a
vigorous northern stream shortwave, will send another deep surface
low through the Great Lakes and Northeast Sunday and Monday, with
a trailing cold front exiting the East Coast. This sets the stage
for continued unsettled weather from the Southern Plains to the
Northeast, with some snowfall possible across northern New England
to end the weekend. Meanwhile, the next system enters the Western
U.S. on Sunday, driving a well developed system and cold front
eastward coast to coast through the remainder of the extended
range.
...Model Guidance/Predictability Assessment...
Models and ensembles show very good agreement on the overall
synoptic pattern through the medium range, with typical questions
in the details. A cut off upper low over the Southwest on Sunday
continues to show some uncertainty regarding timing and ejection
eastward early next week/interactions with approaching Western
U.S. troughing. The GFS continues to struggle run to run with
handling of this energy, so a non-GFS consensus was preferred for
this system. Elsewhere, the deterministic models show good
agreement with both the northern stream energy through the Great
Lakes and Northeast Days 3-4, as well as amplifying Western U.S.
troughing progressing from the West on Sunday, across the Central
Plains, and into the Northeast next Thursday. WPCs blend leaned
more on the ECMWF days 3-4, with smaller contributions from the
rest of the deterministic guidance. Increased the usage of the
ensemble means days 5-7 just to mitigate the smaller scale
differences, but continued inclusion of the ECMWF for some
increased strength and definition of systems. This resulted in
good continuity with the previous WPC forecast as well.
...Weather/Threats Highlights...
Widespread showers and thunderstorms are likely ahead of the cold
front on Sunday from the Southeast into the Mid-Atlantic, with
moderate to locally heavy rainfall possible in spots. Given heavy
rainfall also expected over the Southeast/Tennessee Valley during
the short range, this may enhance a possible flooding threat for
some areas. Expect some showers farther west into Texas as well
along the trailing frontal boundary. The associated deepening
surface low into the Northeast Sunday-Monday should result in
accumulating snowfall across portions of northern New England, as
well as gusty winds across much of the Northeast.
The next system into the West will bring another round of rain and
mountain snow to the region early next week. As the cold front
enters the Central U.S. by Monday/Tuesday, it should tap into Gulf
of Mexico moisture to produce showers and storms ahead of it
initially across Texas and expanding northeastward into the
Tennessee and Ohio Valleys by the middle of next week. Locally
heavy rainfall is possible, but the details on this are dependent
on intensity and timing of the Southwest U.S. closed low and
interactions with the Western-Central U.S. trough.
East Coast states begin above average on Sunday, through trend
back towards normal Monday/Tuesday following the passage of the
cold front. Above normal temperatures will also steadily progress
eastward from the West to the Plains and the Midwest/parts of the
East by middle of next week underneath of upper level ridging. The
greatest anomalies are expected across the Northern Plains where
daytime highs 15-25 degrees above normal are possible Sunday and
Monday. The upper level trough into the Pacific Northwest will
bring temperatures back down towards normal or below normal in the
same regions by early to mid next week.
Santorelli
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