(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.
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 280814
SPC AC 280814
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0314 AM CDT Wed Jul 28 2021
Valid 311200Z - 051200Z
...Saturday/Day 4 to Monday/Day 6...
A broad cyclonic flow pattern is forecast this weekend across the
north-central and northeastern United States. A cold front is
forecast to move southeastward across the north-central states. On
Saturday, the front should be located from the central Plains to the
upper Mississippi Valley. The front is forecast to move to the
southern Plains and Tennessee Valley by Monday. Thunderstorm
development will be possible each afternoon and evening along parts
of the front. Moderate instability and adequate deep-layer shear
will likely be sufficient for a marginal severe threat, in areas
where low-level lapse rates become steep. A greater-magnitude severe
threat will be possible, but this will depend upon the mesoscale
setup, which is unpredictable at this time.
...Tuesday/Day 7 and Wednesday/Day 8...
The medium-range models move the cold front southward into the Gulf
Coast states on Tuesday and stall the front near the coast of the
Gulf of Mexico on Wednesday. Thunderstorms will again be possible
along and near the front. Instability and deep-layer shear are
forecast to be strong enough for a marginal wind-damage threat,
mainly during each afternoon. Mesoscale uncertainty is too high to
warrant issuing a threat area.
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