Day 4-8 Severe Weather Outlook Issued on Nov 21, 2020
Updated: Sat Nov 21 09:47:02 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
Tue, Nov 24, 2020 - Wed, Nov 25, 2020
D7
Fri, Nov 27, 2020 - Sat, Nov 28, 2020
D5
Wed, Nov 25, 2020 - Thu, Nov 26, 2020
D8
Sat, Nov 28, 2020 - Sun, Nov 29, 2020
D6
Thu, Nov 26, 2020 - Fri, Nov 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 210945
SPC AC 210945
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CST Sat Nov 21 2020
Valid 241200Z - 291200Z
...DISCUSSION...
At least an isolated/marginal severe threat should exist on Day
4/Tuesday across parts of the southern Plains into the Ozarks and
lower MS Valley as an upper trough/low ejects eastward over these
regions. Low-level moisture return ahead of a surface low and
related cold front may be sufficient to support surface-based storms
from Tuesday afternoon onward. Deep-layer shear appears more than
sufficient for organized severe storms, but some uncertainty exists
regarding how much instability will ultimately develop. Given this
uncertainty, will hold off for now on including a 15% severe area on
Day 4/Tuesday across any portion of the southern Plains vicinity,
but will reevaluate this possibility in future outlooks.
As the upper trough/low continues east-northeastward across the
central/eastern CONUS on Day 5/Wednesday, a low-end/marginal severe
threat may continue across parts of the lower MS Valley and
Southeast. However, medium-range guidance begins to diverge in the
placement and amplitude of the upper trough/low by Wednesday
evening. It also appears possible that any storms ongoing Wednesday
morning across the lower MS Valley/Mid-South may outpace the
low-level moisture return across the Southeast through the day.
Given these large-scale pattern predictability issues and concerns
about sufficient instability across the warm sector, a 15% severe
area has not been included across the lower MS Valley into the
Southeast for Day 5/Wednesday.
Substantial differences in the synoptic-scale pattern across the
CONUS continue from Day 6/Thursday through the end of the forecast
period. Even so, there appears to be some signal for another
large-scale upper trough to move from the western CONUS to the
Plains in the Day 7/Friday to Day 8/Saturday time frame. Depending
on the evolution of this upper trough/low and how much low-level
moisture return occurs ahead of it, there may be an increase in
severe potential across portions of the southern Plains and lower MS
Valley from Day 7/Friday into Day 8/Saturday. Regardless,
predictability remains far too low to delineate any severe areas at
this extended time frame.
..Gleason.. 11/21/2020
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