811
ACUS01 KWNS 201956
SWODY1
SPC AC 201954

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0254 PM CDT Fri Sep 20 2024

Valid 202000Z - 211200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
MIDWEST...CENTRAL PLAINS...AND NORTHERN HIGH PLAINS...

...SUMMARY...
Isolated strong to severe thunderstorms are possible during the late
afternoon over parts of the Midwest including southwest Lower
Michigan, Illinois, and Indiana. Isolated strong to severe storms
are also possible across parts of the south-central Plains and the
northern High Plains.

...20Z Update...
No changes are needed to the ongoing forecast. See the previous
discussion for additional details.

..Wendt.. 09/20/2024

.PREV DISCUSSION... /ISSUED 1136 AM CDT Fri Sep 20 2024/

...Central Plains...
Low-level moisture will advect north-northwestward throughout the
day associated with a warm front. As a result, low to mid 60s
dewpoints will likely be in place across south-central/southeast KS
during the late afternoon. Dewpoints will likely be in upper 50s
farther west in southwest KS, with notably drier conditions across
the adjacent TX/OK Panhandles where downsloping southwesterly
surface winds are likely.

Southwesterly flow aloft ahead of the approaching upper low will
advect steep mid-level lapse rates northeastward through the
southern High Plains into western portions of the central Plains.
Modest buoyancy is anticipated during the late afternoon where these
lapse rates overlay the more favorable low-level moisture across
southern KS. Limited large-scale ascent and low-level confluence
near the warm front are anticipated over this region as well, with
isolated to widely scattered high-based thunderstorms anticipated.
Vertical shear will be modest, but still strong enough for
persistent/organized storm structures, and the potential for some
strong gusts with the more robust storms. Some isolated hail is also
possible over south-central KS where buoyancy is maximized.

Low-level moisture will continue advection northward during the
evening and overnight, with a strengthening low-level jet
anticipated as well. Consequently, additional thunderstorm
development is expected after 04Z over northeast KS and adjacent far
southeast NE and northwest MO. Isolated hail is possible with the
strongest storms.

...Midwest including Illinois/Indiana to Lower Michigan...
Upper 60s to low 70s dewpoints are expected from southwest Lower MI
southwestward across western IN, southern IL, and southeast MO.
Daytime heating of this moist low-level air mass will yield a
moderately unstable and uncapped air mass ahead of the approaching
front, and thunderstorm development is anticipated as the front
interacts with this airmass. Moderate vertical shear will be in
place, but poor lapse rates and notable mid-level dry air could make
updraft maintenance difficult. A multicellular storm mode is
anticipated. Highest storm coverage is expected over southwest Lower
MI and western IN, with warm mid-level temperatures tending to limit
coverage farther southwest. Locally strong wind gusts will be the
primary severe risk, with isolated, marginally severe hail possible
as well.

...Northern Montana/northwest North Dakota...
At least widely scattered low-topped thunderstorms should develop
across northern Montana and/or move into the region from southern
Alberta as a cold front moves southeastward. This will be influenced
by a southeastward-digging shortwave trough and a related
strengthening of cyclonic westerlies within its base. Even with
modest overall buoyancy, a diurnal steepening of low-level lapse
rates and strengthening low/mid-tropospheric westerlies could
potentially yield severe-caliber convectively enhanced wind gusts
late this afternoon through around sunset.

$$