Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Sat Aug 16 2025
Valid 161630Z - 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 Midwest and
Great Lakes region.
...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.
..Mosier/Wendt.. 08/16/2025
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