(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 020839
SPC AC 020839
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0339 AM CDT Mon Aug 02 2021
Valid 051200Z - 101200Z
...DISCUSSION...
On Thu/D4, a dwindling upper low will move from the upper OH Valley
into NY, with 35-40 kt 500 mb winds across the Mid Atlantic. At the
surface, a weak low will move roughly from NC toward the Delmarva as
a warm front lifts north across NJ and into southern New England.
While ample moisture will be available for storms, significant
precipitation is expected through the period, and shear will be
marginal. While isolated strong to severe storms cannot be ruled
over parts of the Mid Atlantic, potential remains too low.
During the Fri/D5 to Sat/D5 time frame, a weakening shortwave trough
is forecast to move from the northern High Plains to the upper MS
Valley, with low pressure developing over SD and moving into MN.
Storms appear most likely Friday evening in a zone of warm advection
from the Dakotas into MN, with marginal instability forecast. Storms
are expected to persist through Sat/D5 into MN and WI as moisture
and instability continue to increase. While there is potential for a
few severe storms in this regime, the weakening wave decreases
predictability.
Behind this lead wave, a stronger shortwave trough is forecast to
affect the northern Plains and upper MS Valley during the Sun/D7 to
Mon/D8 period. Although predictability is low, this type of pattern
may result in severe storms, as persistent southerly low-level winds
bring a return of upper 60s and lower 70s F dewpoints to the region.
Strong instability may develop, and the Dakotas, MN and WI remain an
area of interest. If model trends persist, severe risk areas may be
added in later outlooks.
..Jewell.. 08/02/2021
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