Mesoscale Discussion 2318
NWS Storm Prediction Center Norman OK
0638 PM CDT Sun Sep 20 2026
Areas affected...portions of southern Missouri...southern
Illinois...southern Indiana...and far western Ohio
Concerning...Severe potential...Watch unlikely
Valid 202338Z - 210145Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated instances of marginally severe hail and wind
possible this evening.
DISCUSSION...A stationary front extends southwest to northeast
across portions of southern MO, southern IL, southern IN, and into
western/central OH. Daytime heating has yielded a moderately
unstable air mass along and south of this feature. Thunderstorm
activity has developed across several regions along and south of
front.
A more focused region of forcing for ascent is moving out of eastern
OK into southern MO, which will likely lead to an uptick in
thunderstorm activity through the evening. Multi-cell clusters will
be favored given the more parallel component of deep layer shear to
the front in this region. Given that deep layer shear is mostly
confined along and north of the front, mode will be fairly
unorganized. However, a few stronger clusters may produce strong to
severe wind through the evening.
Further east across portions of southern IL, IN, and western OH,
transient supercells have developed near and south of the front.
Within this region, deep layer ascent is more negligible aside from
weak frontal convergence. Additionally, though the air mass remains
moderately unstable, warm mid-level temperatures will likely work
against sustained severe convection. An isolated marginally severe
wind and hail risk may continue for another hour or so past sunset.
..Thornton/Guyer.. 09/20/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...ILN...LMK...IWX...IND...PAH...ILX...LSX...LZK...
SGF...
LAT...LON 38009294 37649359 37129342 36549284 36489205 38818489
39298355 39908329 40208361 40338416 40418617 39279035
38009294
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
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