086  
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  
 
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