Day 4-8 Severe Weather Outlook Issued on Aug 25, 2021
Updated: Wed Aug 25 09:01:03 UTC 2021
Day 4 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
15 %
107,782
3,507,368
Minneapolis, MN...Sioux Falls, SD...Duluth, MN...Plymouth, MN...Brooklyn Park, MN...
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, Aug 28, 2021 - Sun, Aug 29, 2021
D7
Tue, Aug 31, 2021 - Wed, Sep 01, 2021
D5
Sun, Aug 29, 2021 - Mon, Aug 30, 2021
D8
Wed, Sep 01, 2021 - Thu, Sep 02, 2021
D6
Mon, Aug 30, 2021 - Tue, Aug 31, 2021
(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 250859
SPC AC 250859
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Wed Aug 25 2021
Valid 281200Z - 021200Z
...DISCUSSION...
Global models appear to be in reasonably good large-scale agreement
with respect to large-scale/synoptic features across the U.S. for
the first couple of days of the medium-range period, before timing
and evolution differences begin to increase -- primarily within the
belt of westerly flow over northern portions of the country, north
of the southern U.S. ridging.
On Sunday/Day 4, a short-wave trough is forecast to advance slowly
eastward across the north-central states. This will allow surface
low pressure initially progged over the South Dakota vicinity to
develop northeastward with time, into southern Manitoba/western
Ontario overnight. Trailing from the low, a cold front crossing
Minnesota during the afternoon/evening time frame should focus storm
development, in the wake of earlier-day storms. With enhanced
southwesterly flow aloft on the eastern fringe of the advancing
upper trough, shear sufficient for organized storms -- and attendant
potential for severe weather -- appears to warrant inclusion of a
15% risk area.
Day 5, as the system advances, storms -- and possibly some severe
risk -- should spread across the Upper Great Lakes region. However,
with potential for early-period storms/cloud cover, questions exist
regarding the afternoon thermodynamic environment. As such, no risk
area will be introduced across this area, at this time.
Beyond Day 5, uncertainty increases as the evolution of the overall
large-scale pattern begins to differ more substantially amongst the
models. Of note, models suggest some potential for a Gulf of Mexico
tropical cyclone that could approach the coast Day 6. In any case,
overall predictability concerns preclude issuance of any additional
risk areas through the end of the period.
..Goss.. 08/25/2021
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