Day 4-8 Severe Weather Outlook Issued on Dec 21, 2020
Updated: Mon Dec 21 09:51:03 UTC 2020
Day 4 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 5 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 6 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 7 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 8 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
D4
Thu, Dec 24, 2020 - Fri, Dec 25, 2020
D7
Sun, Dec 27, 2020 - Mon, Dec 28, 2020
D5
Fri, Dec 25, 2020 - Sat, Dec 26, 2020
D8
Mon, Dec 28, 2020 - Tue, Dec 29, 2020
D6
Sat, Dec 26, 2020 - Sun, Dec 27, 2020
(All days are valid from 12 UTC - 12 UTC the following day)
Note: A severe weather area depicted in the Day 4-8 period indicates 15%, 30% or higher probability for severe thunderstorms within 25 miles of any point.
PREDICTABILITY TOO LOW is used to indicate severe storms may be possible based on some model scenarios. However, the location or occurrence of severe storms are in doubt due to: 1) large differences in the deterministic model solutions, 2) large spread in the ensemble guidance, and/or 3) minimal run-to-run continuity.
POTENTIAL TOO LOW means the threat for a regional area of organized severe storms appears unlikely (i.e., less than 15%) for the forecast day.
Forecast Discussion
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 210949
SPC AC 210949
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CST Mon Dec 21 2020
Valid 241200Z - 291200Z
...DISCUSSION...
A deep and mature upper trough is expected to cover much of the
central and eastern CONUS early D4/Thursday. Primary low associated
with this system will likely be occluded over Ontario but secondary
cyclogenesis is anticipated over the Southeast, with the resulting
low then moving quickly northeastward along the lee of the
Appalachians into the northern Mid-Atlantic. Some severe potential
may develop ahead of this low and its attendant cold front as it
moves quickly eastward. However, differences within the guidance
regarding frontal timing as well as uncertainty regarding antecedent
moisture return currently limit predictability.
High pressure will likely build across the central CONUS in the wake
of the upper trough on D5/Friday and across the eastern CONUS on
D6/Saturday. A shortwave is currently expected to move across the
Intermountain West on D6/Saturday and across the Plains D7/Sunday.
Moisture return ahead of this system will likely remain confined to
central/east TX and the Lower MS Valley. Instability will be limited
even within this corridor of return flow and severe potential
currently appears very limited.
..Mosier.. 12/21/2020
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