Day 4-8 Severe Weather Outlook Issued on Sep 21, 2020
Updated: Mon Sep 21 08:54:03 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, Sep 24, 2020 - Fri, Sep 25, 2020
D7
Sun, Sep 27, 2020 - Mon, Sep 28, 2020
D5
Fri, Sep 25, 2020 - Sat, Sep 26, 2020
D8
Mon, Sep 28, 2020 - Tue, Sep 29, 2020
D6
Sat, Sep 26, 2020 - Sun, Sep 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 210852
SPC AC 210852
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Mon Sep 21 2020
Valid 241200Z - 291200Z
...DISCUSSION...
Depending on the progression of Tropical Cyclone Beta, some severe
threat may persist over parts of the lower MS Valley on Day
4/Thursday as it moves northeastward and merges with a weak
mid-level trough. Considerable uncertainty exists regarding Beta's
placement, and the marginal forecast shear/instability across the
lower MS Valley suggest no severe probabilities are warranted at
this time.
Farther west, an upper trough should advance eastward from the
Pacific Northwest to the northern/central Plains on Day 5/Friday.
Low-level moisture is forecast to gradually increase ahead of this
upper trough across parts of the Plains into the Upper Midwest and
MS Valley. Warm mid-level temperatures may keep the warm sector
capped across the Upper Midwest through much of the day Friday,
although deep-layer shear is forecast to be rather strong.
An isolated/marginal severe risk may exist this upcoming weekend
ahead of a cold front across a fairly broad portion of the CONUS
extending from parts of the southern Plains to the Great Lakes.
However, details remain unclear regarding the timing/amplitude of
the eastward-moving upper trough and related surface features.
Depending on this upper trough's evolution, some severe risk may
continue across parts of the eastern CONUS into early next week.
Regardless, far too much uncertainty exists to include 15% severe
probabilities at this extended time frame.
..Gleason.. 09/21/2020
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