Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Thu Mar 25 2021
Valid 12Z Sun Mar 28 2021 - 12Z Thu Apr 01 2021
...Overview...
Guidance overall agrees in showing an amplified but generally
progressive upper level pattern during the medium range period,
bolstering forecast confidence and WPC forecast continuity. This
should be especially evident with two main northern stream
systems. The first, a vigorous shortwave trough, 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 the
northern tier of the Northeast 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. Meanwhile, a separated
southern stream flow may initially be slower to progress out
through the southern Rockies/Plains Sun/Mon before shearing with
continued uncertainty over the east-central U.S..
...Model Guidance/Predictability Assessment...
Models and ensembles continue to show very good agreement on the
overall synoptic pattern through the medium range, with typical
questions in the details. A cutoff upper low over the Southwest
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 less progressive non-GFS
consensus was preferred for this system. This solution seems
better supported by ensembles and initial separated flow nature.
The 12 UTC ECMWF/Canadian and GEFS ensemble mean remain less
progressive compared to the GFS with this system. Elsewhere, the
deterministic models show good agreement. The WPC medium range
product suite was primarily derived from a composite blend of the
00 UTC ECMWF/UKMET/Canadian days 3-5 (Sun-Tue). Used a composite
of the 06 UTC GFS/GEFS, 00 UTC ECMWF/Canadian/ECENS mean and the
13 UTC National Blend of Models for days 7/8 (next Wed/Thu). This
maintains good WPC product continuity and is consistent with the
bulk of newer 12 UTC guidance.
...Weather/Threats Highlights...
It remains the case that 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/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
Hazards:
- Heavy precipitation across portions of the Northeast, Sun, Mar
28.
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, the Southern
Appalachians, and the Tennessee Valley, Wed, Mar 31.
- Heavy snow across portions of the Pacific Northwest and the
Northern Great Basin, Sun, Mar 28.
- Heavy snow across portions of the Northern Rockies, Mon, Mar 29.
- Severe weather across portions of the Southeast and the
Mid-Atlantic, Sun, Mar 28.
- Flooding possible across portions of the Northeast, the Lower
Mississippi Valley, the Ohio
Valley, and the Tennessee Valley.
- Flooding occurring or imminent across portions of the
Middle/Lower Mississippi Valley, and the
Ohio Valley.
- High winds across portions of the Northern Plains, Mon-Tue, Mar
29-Mar 30.
- High winds across portions of the Mid-Atlantic and the
Northeast, Sun-Mon, Mar 28-Mar 29.
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