Day 4-8 Severe Weather Outlook Issued on Mar 20, 2021
Updated: Sat Mar 20 08:51:03 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
Tue, Mar 23, 2021 - Wed, Mar 24, 2021
D7
Fri, Mar 26, 2021 - Sat, Mar 27, 2021
D5
Wed, Mar 24, 2021 - Thu, Mar 25, 2021
D8
Sat, Mar 27, 2021 - Sun, Mar 28, 2021
D6
Thu, Mar 25, 2021 - Fri, Mar 26, 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 200849
SPC AC 200849
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Sat Mar 20 2021
Valid 231200Z - 281200Z
...DISCUSSION...
A compact upper low/shortwave trough over the south-central U.S. on
Day 4/Tue will lift north/northeast toward the Upper Midwest/Great
Lakes vicinity as another shortwave trough digs southward across the
southwestern U.S./northern Mexico. A surface low will lift
north/northeast in tandem with the upper system, while a cold front
extends south/southwest from the mid-MS Valley into the Edwards
Plateau vicinity in TX. Some strong to severe convection could
develop in the warm sector ahead of the front from the lower MS
Valley into the Upper Texas Coast vicinity, but instability is
forecast to remain modest while stronger ascent will be lifting
northeast of the region. This should limit overall magnitude of
severe potential, precluding probabilities at this time.
Some severe potential could persist near the TX coast eastward along
the central Gulf coast on Day 5/Wed. However, a surface low is
forecast to develop south of the TX coast over the western Gulf.
This could maintain a warm front just offshore from the central Gulf
coast, resulting in mainly elevated convection is a warm advection
regime ahead of the next upper shortwave trough. Severe potential
will largely be dependent on the position of this warm front.
Medium-range guidance varies on the position of this boundary,
resulting in too much uncertainty to include severe probabilities.
The low over the western Gulf should develop northeastward sometime
on Day 6/Thu, as an upper trough over the Plains ejects eastward.
Strong deep-layer southwesterly flow will spread across the
southeastern U.S., while increasing southerly low level flow brings
richer Gulf moisture further inland ahead of an eastward-advancing
cold front. This could bring another bout of severe potential to
much of the South, but the timing of the upper trough, strengthen of
the surface low and quality of the thermodynamic environment remain
uncertain.
By the end of the period, another trough will deepen over the
western U.S. and eject over the southern Plains. While this pattern
would typically favor another round of severe potential, the cold
frontal passage through the southern U.S. around Day 6/Thu could
limit moisture across the Plains into portions of the lower MS
Valley, and forecast confidence at this time frame is low.
..Leitman.. 03/20/2021
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