Day 4-8 Severe Weather Outlook Issued on Apr 19, 2021
Updated: Mon Apr 19 08:56:04 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
15 %
105,863
16,582,088
San Antonio, TX...Dallas, TX...Austin, TX...Fort Worth, TX...Oklahoma City, OK...
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, Apr 22, 2021 - Fri, Apr 23, 2021
D7
Sun, Apr 25, 2021 - Mon, Apr 26, 2021
D5
Fri, Apr 23, 2021 - Sat, Apr 24, 2021
D8
Mon, Apr 26, 2021 - Tue, Apr 27, 2021
D6
Sat, Apr 24, 2021 - Sun, Apr 25, 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 190854
SPC AC 190854
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Mon Apr 19 2021
Valid 221200Z - 271200Z
...DISCUSSION...
A shortwave trough should move eastward across the Southwest on Day
4/Thursday. Low-level moisture return appears likely across parts of
the southern Plains into Day 5/Friday, as lee cyclogenesis occurs
across the southern High Plains ahead of the approaching upper
trough. Run-to-run consistency over the past several runs of the
deterministic ECMWF lends confidence that the shortwave trough
should eject eastward over the southern Plains on Friday. Increasing
low-level moisture to the east of a dryline/cold front and steep
mid-level lapse rates should support at least moderate instability
in a corridor across parts of OK and TX by Friday afternoon. Strong
mid-level flow and related deep-layer shear appear more than
sufficient for organized severe storms, including supercells. As
mid-level height falls/ascent overspread the warm sector, robust
convective development should occur, with at least isolated severe
storms potentially spreading eastward towards southeast TX Friday
evening/night. Confidence in this scenario occurring has increased
enough to include a 15% severe area for Friday.
Some severe risk may continue across parts of the lower MS Valley
and Southeast late Friday night into this upcoming weekend, but
details regarding the eastward progression of the upper trough and
subsequent convective evolution remain unclear. If a severe threat
does develop, then it may focus along/near parts of the central Gulf
Coast on Day 6/Saturday where low-level moisture return is forecast
to be greatest. Regardless, confidence is not high enough to include
a 15% severe area at this time. Depending on how quickly a surface
cold front moves eastward, a lingering severe risk may persist
across some portion of the Southeast into Day 7/Sunday. Finally,
medium-range guidance suggests that a large-scale upper trough may
develop eastward across the western states and towards the High
Plains early next week. Gradually increasing low-level moisture
return across the Plains may eventually lead to some severe risk,
but predictability is quite low at this extended time frame.
..Gleason.. 04/19/2021
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