Day 4-8 Severe Weather Outlook Issued on Mar 21, 2021
Updated: Sun Mar 21 08:37:03 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, Mar 24, 2021 - Thu, Mar 25, 2021
D7
Sat, Mar 27, 2021 - Sun, Mar 28, 2021
D5
Thu, Mar 25, 2021 - Fri, Mar 26, 2021
D8
Sun, Mar 28, 2021 - Mon, Mar 29, 2021
D6
Fri, Mar 26, 2021 - Sat, Mar 27, 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 210835
SPC AC 210835
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0335 AM CDT Sun Mar 21 2021
Valid 241200Z - 291200Z
...DISCUSSION...
Medium-range guidance is fairly consistent in depicting a
progressive upper-level pattern during the Day 4-8 period. A mean
upper-level trough will persist across much of the CONUS, as several
shortwave troughs embedded in larger-scale flow focus potential for
heavy rainfall and perhaps some severe potential.
Day 5/Thu could see a broader area of severe potential across parts
of Texas into the Deep South. A compact shortwave trough is forecast
to pivot east/northeast across the Lower MS Valley, though the
timing and intensity of this feature still varies considerably
between the GFS and ECMWF. The attendant surface features likely
still show large spread in timing and location. The GFS shows a 1000
mb surface low over southern OH 00z Fri, while the ECMWF has a 993
mb low over northwest AR. This clearly has implications on the
quality of the warm sector and the location/timing of convection.
Nevertheless, trends will be monitored for increasing severe
potential on Day 5/Thu across the Lower MS/TN Valley/Central Gulf
Coast vicinity.
How the surface pattern evolves on Thursday will have big
implications for any continued severe threat into Day 6/Fri across
portions of the Southeast and Mid-Atlantic and confidence is low
during this period. Model spread continues to vary considerably into
the weekend, through some severe potential could persist/redevelop
across the central Gulf coast states, as an upper ridge shifts
eastward across the West and the larger-scale upper trough that
persisted through much of the forecast period finally ejects
eastward. However, uncertainty remains too high to include severe
probabilities at this time.
..Leitman.. 03/21/2021
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