(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 130839
SPC AC 130839
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0339 AM CDT Thu Aug 13 2020
Valid 161200Z - 211200Z
...Sunday/Day 4 and Monday/Day 5...
On Sunday, the medium range models are in good agreement with an
upper-level trough in the lower Great Lakes and northwest mid-level
flow from the Great Plains eastward to the southern Appalachians. By
Sunday afternoon, a cold front is forecast to be located from the
Great Lakes to the mid Mississippi Valley, with the western end of
the front in the southern Plains. Isolated thunderstorms will be
possible along the front during the late afternoon and early
evening. Moderate instability and relatively weak deep-layer shear
will be sufficient for a marginal severe threat. But confidence for
a severe threat in a specific area is low.
On Monday, the models remain in decent agreement. A cold front is
forecast to move into the Southeast with an axis of instability
extending from the Gulf Coast states westward into central Texas.
Marginally severe thunderstorms will be possible Monday afternoon
along the front, especially in locations that heat up the most.
However, uncertainty is considerable for Monday's forecast.
...Tuesday/Day 6 to Thursday/Day 8...
From Tuesday to Thursday, models solutions diverge. While most
models have an upper-level ridge in the western U.S. and an
upper-level trough in the eastern U.S., the distribution of
instability is widely varied. The GFS develops a pocket of moderate
instability each afternoon from eastern sections of the central
Plains eastward into the Missouri Valley. The ECMWF develops pockets
of instability primarily in the northern Plains each afternoon.
Thunderstorms associated with an isolated severe threat will be
possible wherever these pockets of instability set up. At this
point, the ECMWF presents the best scenario for a severe threat
because deep-layer shear is expected to be stronger in the northern
Plains. But confidence in any one of these scenarios is low at this
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