Day 4-8 Severe Weather Outlook Issued on Apr 17, 2021
Updated: Sat Apr 17 08:39:02 UTC 2021
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, Apr 20, 2021 - Wed, Apr 21, 2021
D7
Fri, Apr 23, 2021 - Sat, Apr 24, 2021
D5
Wed, Apr 21, 2021 - Thu, Apr 22, 2021
D8
Sat, Apr 24, 2021 - Sun, Apr 25, 2021
D6
Thu, Apr 22, 2021 - Fri, Apr 23, 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 170836
SPC AC 170836
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0336 AM CDT Sat Apr 17 2021
Valid 201200Z - 251200Z
...DISCUSSION...
As large-scale upper troughing amplifies over the central CONUS on
Day 4/Tuesday, a low-amplitude shortwave trough should advance
eastward across FL and into the western Atlantic. A surface front
across the FL Peninsula may advance northward through the day, and
some potential for isolated strong to severe storms may exist
Tuesday along/south of this boundary. Still, the low-amplitude
nature of the upper trough and weak mass response at the surface
suggest any severe threat will probably remain limited.
Medium-range guidance is in reasonably good agreement that further
amplification of an upper trough/low should occur as it moves
eastward across the OH Valley and into the Mid-Atlantic/Northeast on
Day 5/Wednesday. Strong low/mid-level flow will be present over
these regions as the upper trough/low passes, and a modest increase
in low-level moisture may occur Wednesday ahead of a surface cold
front. At this point, the potential for enough instability to
develop to support an organized severe threat appears too uncertain
to include any severe probabilities across the Mid-Atlantic.
Farther west, a shortwave trough may advance from the Southwest
across the southern Plains and Southeast from Day 6/Thursday through
Day 8/Saturday. There is fairly large spread in deterministic
guidance regarding the evolution and ejection of this feature. If a
more progressive solution occurs, as suggested by some guidance,
then substantial low-level moisture return may occur from late
Thursday into Friday across parts of the southern Plains. Some
severe risk could materialize across this region Friday as a
dryline/cold front sweep eastward. This possible severe risk may
then continue across the lower MS Valley and portions of the
Southeast on Saturday. Regardless, given the considerable
uncertainty regarding the progression of the shortwave trough, and
its impact on the degree of low-level moisture return, it appears
premature to include any severe probabilities for this scenario at
this time.
..Gleason.. 04/17/2021
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