907  
FXUS63 KILX 282350  
AFDILX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE LINCOLN IL  
650 PM CDT MON JUL 28 2025  
   
KEY MESSAGES
 
 
- A HEAT ADVISORY REMAINS IN EFFECT FOR PORTIONS OF CENTRAL AND  
SOUTHEAST ILLINOIS THROUGH TUESDAY AFTERNOON FOR HEAT INDEX  
VALUES BETWEEN 100-110 F.  
 
- A STRONG COMPLEX OF THUNDERSTORMS WILL SHIFT SOUTHEAST TOWARD  
WESTERN ILLINOIS OVERNIGHT, BRINGING A POTENTIAL FOR DAMAGING  
STRAIGHT LINE WINDS.  
 
- ADDITIONAL THUNDERSTORMS WILL DEVELOP ALONG A SLOW-MOVING COLD  
FRONT WEDNESDAY, BRINGING A RISK OF LARGE HAIL, DAMAGING WINDS,  
TORRENTIAL RAINFALL, AND FREQUENT LIGHTNING.  
 

 
   
DISCUSSION
 
 
ISSUED AT 255 PM CDT MON JUL 28 2025  
 
EARLY AFTERNOON SATELLITE AND SFC ANALYSIS DEPICTS A FEW KEY  
FEATURES THAT WILL DRIVE THE SYNOPTIC PATTERN OVER THE NEXT 24  
HOURS. OF IMMEDIATE IMPORTANCE, A REMNANT OUTFLOW BOUNDARY HAS  
PUSHED INTO SOUTHERN ILLINOIS. THIS BOUNDARY MAY DRIFT A LITTLE  
FURTHER NORTH THROUGHOUT THE REMAINDER OF THE AFTERNOON AS  
SOUTHERLY LOW-LEVEL FLOW IMPINGES ON IT. A QUICK GLANCE AT  
SATELLITE IMAGERY DEPICTS A GROWING CUMULUS FIELD ON THE SOUTH  
SIDE OF THIS BOUNDARY, WITH THE NORTHERN EDGE BUTTING UP AGAINST  
I-70. ROBUST INSTABILITY (MLCAPE > 4000 J/KG) AND JUST ENOUGH DEEP  
LAYER SHEAR (20-25 KTS) IS BEING ANALYZED BY RECENT RAP GUIDANCE  
ACROSS SE ILLINOIS AMID MODEST MID-LEVEL LAPSE RATES (6-6.6 C/KM)  
AND DRY MID-LEVEL AIR. UPDRAFTS SHOULD STRUGGLE TO GET GOING IN  
THIS ENVIRONMENT, BUT WE WILL NEED TO MONITOR FOR THE POTENTIAL  
FOR A FEW STRONG MULTI-CELL CLUSTERS TO DEVELOP IN THE VICINITY OF  
THE OUTFLOW BOUNDARY SHOULD A FEW UPDRAFTS OVERPERFORM. POTENTIAL  
HAZARDS THIS AFTERNOON AND EVENING WOULD FAVOR DOWNBURST WINDS  
(50-60 MPH), SMALL HAIL, TORRENTIAL DOWNPOURS AND CLOUD-TO-GROUND  
LIGHTNING.  
 
ANOTHER SYNOPTIC FEATURE WE ARE WATCHING CLOSELY IS A SHORTWAVE  
TROUGH CRESTING THE TOP OF THE HEAT RIDGE. THIS SHORTWAVE IS  
CURRENTLY OVER THE DAKOTAS AND IS FORECAST TO PUSH SOUTHEASTWARD  
INTO THE UPPER-MISSISSIPPI VALLEY OVERNIGHT. MOST MODEL GUIDANCE  
DEPICTS A STRENGTHENING MCS FOLLOWING THE PATH OF THE UPPER  
FORCING (SHORTWAVE), EVENTUALLY PUSHING INTO PORTIONS OF EASTERN  
IOWA AND SOUTHWEST WISCONSIN AFTER 06Z/1AM. SOME UNCERTAINTY  
REMAINS WITH EXACTLY HOW THIS MCS EVOLVES IN TIME AND SPACE. WHILE  
IT MAKES GOOD CONCEPTUAL SENSE FOR THE MCS TO FOLLOW THE UPPER  
FORCING, WE DO OCCASIONALLY SEE THE CONVECTIVE ACTIVITY SHOW A  
TENDENCY TO WANT TO FOLLOW THE MUCAPE GRADIENT. RECENT GUIDANCE  
FROM THE HREF AND WOFS POSITIONS A 2000-4000 J/KG MUCAPE GRADIENT  
ALONG A LINE EXTENDING FROM DES MOINES TO MACOMB. AND IT'S HERE THAT  
THE FORECAST UNCERTAINTY LIES.  
 
THE MOST LIKELY SCENARIO IS FOR THE MCS TO FOLLOW THE UPPER  
FORCING (SHORTWAVE) INTO SOUTHERN WISCONSIN WHERE IT WILL RAPIDLY  
DECAY AMID ROBUST MID-LEVEL DRY AIR AND SLIGHTLY LESS UNSTABLE  
CONDITIONS. A REASONABLE ALTERNATIVE WOULD BE FOR THE MCS TO FAN  
OUT, WITH SOME HEALTHY DEVELOPMENT ON THE SOUTHERN PERIPHERY (SE  
IA/NE MO/W IL) OF THE UPPER FORCING TOWARD THE MUCAPE GRADIENT,  
BUT DECAYING ON THE EASTERN PERIPHERY (S WI/N IL). THE OUTLYING  
SOLUTION WOULD BE FOR THE MATURE MCS TO NOT DECAY, BUT INSTEAD  
ACCELERATE AND MAINTAIN ITSELF FOR A LONG-DURATION BOW ECHO OR  
DERECHO. NO CAM CURRENTLY SHOWS THE OUTLIER, BUT THAT ISNT  
UNCOMMON FOR DERECHOS THIS TIME OF YEAR (SEE AUG 10 2020, JUN 29  
2023, AND JUL 15 2024).  
 
REGARDLESS OF THE EVOLUTION OF UPSTREAM CONVECTION OVERNIGHT, IT  
WILL LIKELY THROW SOME CONVECTIVE DEBRIS INTO CENTRAL ILLINOIS.  
THIS WOULD THEORETICALLY TAMP DOWN TEMPERATURES AND ATTENDANT HEAT  
INDEX VALUES FOR WEDNESDAY AFTERNOON, PARTICULARLY ACROSS OUR  
NORTHERN COUNTIES NEAR AND NORTH OF I-74. AS A RESULT, WE HAVE  
TRIMMED OUR CURRENT HEAT ADVISORY BUT DID EXTEND IT INTO WEDNESDAY  
AFTERNOON.  
 
ATTENTION THEN TURNS TOWARD TUESDAY NIGHT AND WEDNESDAY AFTERNOON  
AS A COLD FRONT SLOWLY SAGS INTO CENTRAL ILLINOIS FROM THE NORTH.  
CAPE/SHEAR PROFILES IN THE VICINITY OF THE FRONT WILL BE CONDUCIVE  
FOR SEVERE WEATHER, WITH A LARGE HAIL AND DAMAGING WIND THREAT  
EVOLVING OVERNIGHT IN AREAS NORTH OF I-72, AND A CONTINUED THREAT  
RE-DEVELOPING LATER WEDNESDAY AFTERNOON IN AREAS NEAR AND SOUTH OF  
I-72. LOCALIZED FLASH FLOODING MAY ALSO BE OF CONCERN AS PWATS  
EXCEED 99TH PERCENTILE OF LATE JULY CLIMATOLOGY, AND WITH MUCH OF  
THE REGION EXCEEDING 150% OF NORMAL RAINFALL OVER THE PAST 30 DAYS.  
 
A MUCH DRIER AND COOLER PATTERN WILL TAKE SHAPE THURSDAY ONWARD IN  
THE WAKE OF THE PASSING COLD FRONT. A MODIFIED AREA OF CANADIAN  
HIGH PRESSURE WILL SLOWLY BUILD ACROSS PORTIONS OF THE MIDWEST AND  
GREAT LAKES, PUSHING DAILY TEMPERATURES 5-10 DEGREES BELOW NORMAL  
FOR LATE JULY AND EARLY AUGUST.  
 
MJA  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)  
ISSUED AT 649 PM CDT MON JUL 28 2025  
 
HIGH PRESSURE WILL BUILD ACROSS CENTRAL ILLINOIS OVERNIGHT  
RESULTING IN LIGHT AND VARIABLE WINDS AND ALLOWING POSSIBLE FOG  
PRODUCTION LATE TONIGHT INTO TUESDAY MORNING. A LINE OF  
THUNDERSTORMS IS STILL EXPECTED TO FORM OVER THE UPPER MIDWEST  
THIS EVENING AND MOVE SOUTHEAST OVERNIGHT. SEVERAL MODELS HAVE  
BACKED OFF ON BRINGING THESE STORMS ALL THE WAY TO CENTRAL  
ILLINOIS, BUT A COUPLE MODELS HANG ON TO THIS IDEA. HAVE TRIMMED  
THE TIMING OF THE PROB30 FOR STORMS BUT MAINTAIN IT FOR THE I-74  
CORRIDOR. WILL REASSESS FOR THE 06Z TAFS TO SEE IF IS FEASIBLE TO  
REMOVE MENTION ALTOGETHER, BUT AT THIS POINT THE MAIN MESSAGE IS  
THAT CONFIDENCE IS DECREASING ON STORMS REACHING CENTRAL ILLINOIS.  
 
DEUBELBEISS  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR ILZ027>031-036>038-  
040>057-061>063-066>068-071>073.  
 
HEAT ADVISORY FROM NOON TO 8 PM CDT TUESDAY FOR ILZ027-029-036-  
037-040>057-061>063-066>068-071>073.  
 

 
 

 
 
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