ACUS01 KWNS 051211
SWODY1
SPC AC 051209

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0709 AM CDT Fri Sep 05 2025

Valid 051300Z - 061200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE TENNESSEE VALLEY AND UPPER OHIO VALLEY...

...SUMMARY...
Scattered damaging winds, isolated severe hail, and a brief tornado
or two are possible from the Upper Ohio to Tennessee Valleys during
the late afternoon and evening.

...Upper OH to TN Valleys...
Water-vapor imagery shows a large gyre centered over Ontario and
cyclonic flow over much of eastern North America.  A series of
mid-level disturbances/speed maxima will rotate through its base
during the Day-1 period, and there are two lead impulses over the
St. Lawrence Seaway and the Upper Great Lakes this morning.  A
weaker impulse associated with convection early this morning over KS
will rapidly move east into the northern part of the OH Valley
through this evening and immediately ahead of a more notable
shortwave trough moving southeast from the Dakotas into the Great Lakes.

A cold front oriented mostly north-south over the Great Lakes from a
surface low will push east during the day, while the trailing
southern portion of the boundary that is west-east oriented,
gradually pushes south and eventually overtakes a residual frontal segment.

Heating ahead of the aforementioned low-amplitude impulse and
strengthening low-level convergence along the boundary will likely
yield scattered to numerous showers/thunderstorms developing in the
late afternoon to early evening.  Much of the stronger mid-level
flow will remain spatially displaced from the warm sector in the
post-frontal airmass except over the Upper OH Valley.  Moderate
buoyancy will favor strong to severe multicells and some supercells
(where shear is stronger).  Isolated severe gusts (55-70 mph) seem
probable which will result in scattered wind damage accompanying the
stronger thunderstorm cores and line segments.  Models differ on the
character of mixing and hodograph size over the southeast OH/WV
portion of the Slight Risk, but low-tornado potential may be
greatest here compared to farther south/southwest over the TN
Valley.  The severe threat will diminish towards late evening given
the extensive overturning and lack of stronger low-level flow/shear
to sustain the threat overnight.

...North TX to Mid-South...
An elongated mid-level thermal trough, characterized by 500-mb
temperatures of -10 to -12 C, will extend into north TX, well to the
south of a persistent vertically stacked cyclone over northern
Ontario.  A copious amount of high cloud cover will tend to result
in high-level lapse rates becoming weaker during the period.  Model
data implies a messy storm mode as isolated to locally scattered
storm coverage ensues during the late afternoon/evening.  An
isolated wind/hail risk may accompany the stronger storms.

..Smith/Broyles.. 09/05/2025

$$
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