ACUS01 KWNS 091249
SWODY1
SPC AC 091248

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Sat Aug 09 2025

Valid 091300Z - 101200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER GREAT LAKES/UPPER MIDWEST...AND EASTERN COLORADO INTO FAR
WESTERN KANSAS...

...SUMMARY...
Multiple severe/damaging wind swaths should occur today centered on
parts of Iowa, northwest Illinois, Wisconsin, and the Upper
Peninsula of Michigan. Large to very large hail will be possible
across parts of eastern Colorado and vicinity this afternoon and evening.

...Upper Great Lakes/Upper Midwest into the Missouri Valley...
A small but intense bowing cluster has produced numerous severe
gusts/damage reports (some 75+ mph) in a narrow corridor early this
morning across south-central NE to western IA. This convection
should continue east-northeastward across parts of central/northern
IA through the rest of the morning, with an enhanced southwesterly
low-level jet providing ample moist inflow. A very unstable airmass
remains in place ahead of a cold front across this area, with MUCAPE
around 3000-3500 J/kg. This large reservoir of buoyancy should
continue to support a severe/damaging wind threat with this cluster
into parts of central/northern IA for at least the next few hours.
See Mesoscale Discussion 1911 for more details on the short-term
severe threat associated with this bowing complex.

Additional thunderstorms have developed along/near the cold front
across a broader portion of the Upper Great Lakes and Upper Midwest.
It still appears probable that multiple swaths of severe/damaging
winds may occur through the afternoon and evening across parts of
these regions as the airmass ahead of these thunderstorms gradually
destabilizes. With rich low-level moisture already in place, strong
to extreme instability should once again develop by this afternoon.
While stronger mid-level flow and related deep-layer shear will tend
to lag the cold front, they should still be sufficient to support
organized convection, mainly linear clusters. Some adjustments have
been made to the Slight Risk to account for the ongoing severe
thunderstorms in IA, as well as additional activity forecast to
occur through the afternoon and evening. The potential for
additional robust convective development tonight across parts of the
MO Valley remains unclear as a southerly low-level jet strengthens
once again. Regardless, have maintained severe probabilities across
southeast NE and vicinity for this possibility.

...Central/Southern High Plains...
A cold front should become nearly stationary by this afternoon
across the south-central High Plains. A favorable low-level,
post-frontal regime for severe convection is expected to develop
across eastern CO by late afternoon. The presence of steep mid-level
lapse rates, moderate instability, and favorable deep-layer shear
will likely support scattered supercells capable of large to very
large hail, localized severe gusts, and possibly a tornado or two
mainly this afternoon into the evening. Across the southern High
Plains, high-based convection may again develop across parts of
eastern NM into the OK/TX Panhandles. This activity could pose a
isolated threat for severe gusts given a very well-mixed boundary layer.

..Gleason/Leitman.. 08/09/2025

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