Day 4-8 Severe Weather Outlook Issued on Mar 15, 2021
Updated: Mon Mar 15 08:43:03 UTC 2021
Day 4 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
15 %
160,513
24,336,438
Jacksonville, FL...Charlotte, NC...Virginia Beach, VA...Raleigh, NC...Norfolk, VA...
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
Thu, Mar 18, 2021 - Fri, Mar 19, 2021
D7
Sun, Mar 21, 2021 - Mon, Mar 22, 2021
D5
Fri, Mar 19, 2021 - Sat, Mar 20, 2021
D8
Mon, Mar 22, 2021 - Tue, Mar 23, 2021
D6
Sat, Mar 20, 2021 - Sun, Mar 21, 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 150841
SPC AC 150841
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CDT Mon Mar 15 2021
Valid 181200Z - 231200Z
...DISCUSSION...
Medium-range models are in reasonable agreement through roughly Day
6 (Saturday Mar. 20), sufficient to offer a reasonable assessment of
convective potential over the CONUS. After Day 6, differences
between the ECMWF and GFS become more obvious, as the next major
upper trough advances across the interior West. With a large area
of strong surface high pressure in place east of the Rockies prior
in advance of this next system, details in terms of timing and
strength -- and related evolution of the surface pattern -- will be
instrumental with respect to moisture return/destabilization
potential when the system eventually emerges into the Plains. Thus
-- with models quite different in evolving the pattern through the
last half of the medium-range period, no convective assessment will
be attempted.
In the mean time, storms -- and associated severe potential -- which
should be ongoing at the start of Day 4 (Thursday) will spread east
of the Appalachians, possibly affecting areas as far north as
southern Virginia and as far south as northern Florida. Timing
differences exist between the GFS and ECMWF, with the slower ECMWF
more favorable for severe weather given the greater degree for
afternoon heating/destabilization across the Carolinas vicinity
ahead of the front, and associated convective band. In any case, a
moist and favorably sheared environment is expected, which should
prove supportive for appreciable severe potential.
As the front moves offshore overnight, and then across the western
Atlantic through the day Friday (Day 5), a large area of high
pressure will expand to encompass most of the U.S. east of the
Rockies. This high should largely remain in place Day 6 (Saturday),
suggesting a couple of days of quiescent conditions with respect to
severe-weather potential. The next increase in risk could occur
with the aforementioned western system, but a more detailed
assessment will be delayed, pending better alignment of model
solutions.
..Goss.. 03/15/2021
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