Day 4-8 Severe Weather Outlook Issued on Apr 18, 2021
Updated: Sun Apr 18 08:52:03 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
Wed, Apr 21, 2021 - Thu, Apr 22, 2021
D7
Sat, Apr 24, 2021 - Sun, Apr 25, 2021
D5
Thu, Apr 22, 2021 - Fri, Apr 23, 2021
D8
Sun, Apr 25, 2021 - Mon, Apr 26, 2021
D6
Fri, Apr 23, 2021 - Sat, Apr 24, 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 180850
SPC AC 180850
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Sun Apr 18 2021
Valid 211200Z - 261200Z
...DISCUSSION...
Low/mid-level winds will likely strengthen across the Mid-Atlantic
and Northeast on Day 4/Wednesday as an upper trough moves eastward
across these regions. There is still some uncertainty regarding how
much low-level moisture will be present ahead of a cold front. If
enough boundary-layer instability develops by Wednesday afternoon,
then strong/damaging winds appear possible with any storms that can
develop along or ahead of the quickly moving front. At this point,
confidence in organized severe convection producing a swath of
damaging winds remains too low to introduce 15% severe
probabilities. Still, some severe risk appears possible from roughly
eastern NC to southern NY, and this region may need to be included
in low severe probabilities in a subsequent outlook.
Low-level moisture return should begin to occur on Day 5/Thursday
across parts of the southern Plains as another upper trough develops
eastward across the Southwest and northern Mexico. There are still
substantial differences in medium-range guidance regarding the
evolution of this upper trough as it ejects over the southern Plains
on Day 6/Friday. Depending the on quality and northward extent of
the low-level moisture return, enough instability may be present to
the east of cold front and dryline to support organized severe
storms Friday across part of the southern Plains. If a more
progressive and amplified upper trough develops eastward as
indicated by some deterministic guidance, then a severe risk may
also occur across parts of the Southeast next weekend. Regardless,
far too much uncertainty remains regarding the timing/amplitude of
the upper trough and placement of related surface features to
include any severe probabilities at this extended time frame.
..Gleason.. 04/18/2021
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