Day 4-8 Severe Weather Outlook Issued on Dec 9, 2020
Updated: Wed Dec 9 08:46:03 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
Sat, Dec 12, 2020 - Sun, Dec 13, 2020
D7
Tue, Dec 15, 2020 - Wed, Dec 16, 2020
D5
Sun, Dec 13, 2020 - Mon, Dec 14, 2020
D8
Wed, Dec 16, 2020 - Thu, Dec 17, 2020
D6
Mon, Dec 14, 2020 - Tue, Dec 15, 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 090844
SPC AC 090844
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0244 AM CST Wed Dec 09 2020
Valid 121200Z - 171200Z
...DISCUSSION...
A low-amplitude shortwave trough embedded within a broader,
large-scale trough centered over the Plains will eject northeast
from the Midwest to the northeastern U.S. on Day 4/Saturday. At the
surface, a low near the mid-MS Valley Saturday morning will develop
northeast to the lower Great Lakes by Day 5/Sunday morning. A cold
front attendant to the low will spread east/southeast across the
Midwest and south-central U.S., extending from western NY/PA
southwestward along the central and western Gulf coast vicinity.
Showers and thunderstorms are expected across parts of the mid/lower
MS Valley into the Mid-South and central Gulf coast on Saturday.
While modest Gulf moisture will return northward ahead of the front,
the boundary layer will remain shallow and meager instability is
forecast, precluding severe thunderstorm concerns.
By Day 5/Sunday, medium range guidance begins to vary considerably
in the evolution of the larger-scale upper trough over the Plains,
and the associated surface pattern. The aforementioned cold front
will likely continue to push offshore the Atlantic coast and Florida
through early Day 6/Monday morning, but severe potential will remain
low. Beyond Sunday, predictability is low given model variability,
but in the mean, a progressive pattern with a series of short
wavelength troughs appears to be likely. This should limit severe
potential as any deep, higher-quality Gulf moisture return would be
unlikely.
..Leitman.. 12/09/2020
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