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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ACUS01 KWNS 161958
SWODY1
SPC AC 161957

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Sat Aug 16 2025

Valid 162000Z - 171200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING AND
TONIGHT OVER PART OF SD...AND THIS AFTERNOON THROUGH TONIGHT OVER
SOUTHEAST MN...SOUTHERN WI...AND NORTHERN IL...

...SUMMARY...
Scattered strong/severe thunderstorms are possible today into
tonight across parts of the northern Great Plains into the Midwest
and Great Lakes regions.

...20Z Update...
The prior forecast reasoning remains valid. Severe probabilities
were reduced in parts of northern/central Wisconsin where prior
convection has stabilized the boundary layer. Elsewhere, only minor
changes were made to the general thunderstorm forecast based on
current observational trends. See the previous discussion as well as
MCDs 1965/1966 for additional information.

..Wendt.. 08/16/2025

.PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Aug 16 2025/

...Upper Midwest into the Mid MS Valley and Upper Great Lakes
Region...
An expansive MCS continues to move eastward across the Upper
Midwest, with a well-defined MCV evident in radar imagery over the
central WI/MN border vicinity. This MCS has continued to gradually
weaken throughout the morning, but a few strong updrafts persist
along its southeastern periphery over central WI. This portion of
the MCS is on the far northeastern periphery of the plume of steeper
mid-level lapse rates that extends from the northern/central High
Plains across the central Plains and into the Mid MS Valley. This
plume is observable in the 12Z sounding from DVN and ILX, which
sampled 700-500 mb lapse rates of 7.8 and 7.2 deg C per km,
respectively. Dewpoints downstream across southern WI, northern IL,
and northern IN are in the low 70s, with upper 60s dewpoints also
covering much of southern Lower MI. The combination of ample
low-level moisture and steep mid-level lapse rates will result in
strong to very strong buoyancy to the south of the MCS from the
MN/IA border into northern/central IL.

Given the lack of a well-defined surface boundary and negligible
large-scale ascent, additional thunderstorm development will be
associated with outflow from with the MCS, which results in greater-than-average uncertainty for the Day 1 period. Ample
moisture and buoyancy downstream of the leading edge of the MCS
suggests the greater severe potential this afternoon/evening will
likely be associated with redevelopment/reintensification of the
MCS. Additionally, even if reintensification does not occur along
the leading edge of the MCS this afternoon, most guidance suggests redevelopment does eventually occur this evening along the southern
periphery of the MCV circulation as it moves into northern/central
WI. Increased severe-wind probabilities (i.e. 15%) were introduced
with this outlook to cover both of these potential scenarios. A
small 15% hail probability was introduce to cover potential for
later evening storms atop the outflow as well.

Storms are possible into northern IN and the Lower MI this afternoon
and evening as well, but the lower buoyancy should temper the
overall coverage and magnitude in these areas.

...SD and Vicinity...
A well-defined but rather weak shortwave trough is currently moving
through western CO/western WY, and will continue northeastward into
eastern WY/western Dakotas by this evening. Similar to yesterday,
high-based storms will develop ahead of the approaching shortwave
and intensify as they move eastward into a progressively more
moist/unstable air mass over west-central SD. Upscale growth into
another nocturnal MCS is forecast by most guidance, with the MCS
tracking northeastward across western/central SD tonight. Strong to
severe gusts are possible with this potential MCS across much of western/central SD.

$$
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