Day 4-8 Severe Weather Outlook Issued on Nov 19, 2020
Updated: Thu Nov 19 09:39:03 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
Sun, Nov 22, 2020 - Mon, Nov 23, 2020
D7
Wed, Nov 25, 2020 - Thu, Nov 26, 2020
D5
Mon, Nov 23, 2020 - Tue, Nov 24, 2020
D8
Thu, Nov 26, 2020 - Fri, Nov 27, 2020
D6
Tue, Nov 24, 2020 - Wed, Nov 25, 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 190937
SPC AC 190937
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0337 AM CST Thu Nov 19 2020
Valid 221200Z - 271200Z
...DISCUSSION...
A progressive upper level pattern is expected during the Day 4-8
period. An upper trough over the Plains on Day 4/Sun will shift
eastward to the Atlantic coast through Day 5/Mon. At the same time,
a surface cold front will sweep east/southeast from the southern
Plains through the Midwest and eastern U.S., moving well offshore
the Atlantic coast by Day 6/Tue. Showers, and perhaps isolated
thunderstorms, are expected to accompany the frontal passage, but
mostly stable boundary-layer conditions will preclude severe
thunderstorm concerns through Day 5/Mon.
As this initial upper trough shifts east of the MS River on Day
5/Mon, an upper ridge will briefly amplify over the Plains.
Meanwhile, a western upper trough will deepen and shift eastward
toward the southern Rockies on Monday, and the central/southern
Plains on Day 6/Tue. Strong deep layer southwesterly flow will
overspread the southern Plains vicinity, and height falls will
result in strengthening lee cyclogenesis developing eastward across
the central/southern Plains Monday night through Tuesday. Increasing
southerly low level flow will transport somewhat modest Gulf
moisture northward. However, medium range guidance is in fairly good
agreement that surface dewpoints as high as the low to mid 60s F are
possible as far north as southern OK. How much destabilization will
ultimately occur remains somewhat uncertain, as the cold frontal
passage on Sunday/Monday could cut-off Gulf return flow more than
guidance currently indicates. Additionally, cloudiness and showers
in a strong warm advection regime could limit destabilization ahead
of the surface low/front. Nevertheless, overall pattern favors at
least some concern for isolated strong/severe thunderstorm potential
across the southern Plains vicinity on Day 6/Tue, but uncertainty
remains too high at this time to introduce probabilities.
Beyond Tuesday, spread among various guidance increases
dramatically, and predictability is low.
..Leitman.. 11/19/2020
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