Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 182235
SWOMCD
SPC MCD 182234
INZ000-ILZ000-190000-
Mesoscale Discussion 1989
NWS Storm Prediction Center Norman OK
0534 PM CDT Mon Aug 18 2025
Areas affected...portions of northern Illinois and northwest Indiana
Concerning...Severe Thunderstorm Watch 599...
Valid 182234Z - 190000Z
The severe weather threat for Severe Thunderstorm Watch 599
continues.
SUMMARY...Several clusters of thunderstorms will remain capable of
strong to occasionally severe gusts this evening. Watch extension or
replacement is being considered, but the longevity of the threat is
uncertain.
DISCUSSION...As of 2230 UTC, several clusters of thunderstorms were
ongoing over northern IL in proximity to WW599. An additional linear
cluster has recently intensified across far eastern IA. A very
unstable but modestly sheared environment remains in place ahead of
these storms over IL and northwest IN. This could support a
continued threat for damaging gusts for a couple hours this evening.
Vertical shear is weaker with southward extent (less than 25 kt)
suggesting a more transient damaging wind risk as storms continue
this evening. Still, some severe risk is possible. With expiration
currently set for 2300 UTC, WW599 may need to be locally extended or
replaced.
..Lyons/Smith.. 08/18/2025
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...IWX...LOT...ILX...DVN...
LAT...LON 40859089 41519035 41878886 41888755 41678688 41328679
40958706 40668762 40608845 40749056 40859089
MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH