716  
FXUS63 KLOT 110505  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
1205 AM CDT FRI JUL 11 2025  
   
KEY MESSAGES
 
 
- SEVERAL WAVES OF SHOWERS AND STORMS ARE POSSIBLE FROM TONIGHT  
THROUGH SATURDAY ACROSS THE AREA. SOME STORMS MAY BE SEVERE  
WITH DAMAGING WINDS AND FLASH FLOODING.  
 
- PROVIDED LOW COVERAGE OF THUNDERSTORMS, FRIDAY MAY BE HOT AND  
HUMID WITH HEAT INDICES NEAR 100 DEGREES.  
 

 
   
MESOSCALE
 
 
ISSUED AT 956 PM CDT THU JUL 10 2025  
 
CLUSTERS OF THUNDERSTORMS, CAPABLE OF PRODUCING TORRENTIAL  
RAINS AND AREAS OF FLOODING, ARE EXPECTED TO CONTINUE TRACKING  
ACROSS A GOOD PORTION OF THE FORECAST AREA INTO THE OVERNIGHT  
HOURS. THE FLOOD WATCH CURRENTLY IN EFFECT UNTIL 7 AM CDT HAS  
BEEN EXPANDED SLIGHTLY SOUTHWARD A TIER OF COUNTIES TO INCLUDE  
LASALLE, GRUNDY AND SOUTHERN WILL COUNTIES IN NORTHERN IL. THE  
THREAT OF LOCALIZED SEVERE WEATHER APPEARS TO BE FOCUSING SOUTH  
OF I-88 LATE THIS EVENING.  
 
LATEST SURFACE ANALYSIS INDICATES A NEARLY STATIONARY WARM  
FRONT WAS LOCATED FROM NEAR KDVN, EAST-SOUTHEAST TO JUST SOUTH  
OF KVYS AND KIKK. CLUSTERS OF STRONG THUNDERSTORMS HAVE BEEN  
TRACKING WEST TO EAST TO THE NORTH OF THE FRONTAL BOUNDARY SINCE  
LATE THIS AFTERNOON, AHEAD OF A CONVECTIVELY-ENHANCED MID-LEVEL  
SHORT WAVE, WITH AN EMBEDDED MCV EVIDENT IN RADAR IMAGERY  
TRACKING EAST NEAR KRFD. STORMS HAVE BEEN PROLIFIC RAINFALL  
PRODUCERS, WITH A COUPLE OF SWATHS OF MRMS RADAR ESTIMATES  
SOLIDLY IN THE 2.50"-4.50" ACROSS PARTS OF WINNEBAGO AND BOONE  
COUNTIES, AS WELL AS NORTHWEST OGLE COUNTY. MAX AMOUNTS IN THE  
5.50" RANGE ON THE NORTH SIDE OF ROCKFORD APPEAR IN LINE WITH  
SOME PERSONAL WEATHER STATION REPORTS. MANY REPORTS OF FLOODING  
HAVE BEEN RECEIVED FROM THOSE AREAS THIS EVENING.  
 
STRONGEST CONVECTION NOW APPEARS TO BE FOCUSING A LITTLE  
FARTHER TO THE SOUTH, FROM THE QUAD CITIES EASTWARD INTO PARTS  
OF LEE AND LIKELY EVENTUALLY LASALLE COUNTIES, IN THE VICINITY  
OF THE FRONTAL ZONE (LIKELY ENHANCED BY OUTFLOW FROM ACTIVITY  
FROM THE NORTH). FARTHER NORTHWEST, PRECIPITATION HAS SUBSIDED  
INTO NORTHWEST IL WITHIN A LIKELY AREA OF SUBSIDENCE BEHIND THE  
AFOREMENTIONED MCV. THIS TREND MAY CONTINUE, THOUGH CAN'T  
COMPLETELY RULE OUT SOME ADDITIONAL DEVELOPMENT THERE. THUS THE  
FOCUS FOR HEAVIEST RAIN (AND A LINGERING THREAT OF ISOLATED  
STRONG WINDS/MARGINAL HAIL) LOOKS TO BE SHIFTING SOUTH OF THE  
I-88 CORRIDOR AND INTO THE I-80 CORRIDOR, WITH TRAINING STORMS  
EXPECTED TO PERSIST INTO THE OVERNIGHT HOURS AS A SOUTHWESTERLY  
30-35 KT LOW LEVEL JET CONTINUES TO IMPINGE ON THE COMBINED  
FRONT/OUTFLOW BOUNDARY. WITH THIS IN MIND, HAVE EXTENDED THE  
FLOOD WATCH A TIER OF COUNTIES TO THE SOUTH TO INCLUDE LASALLE,  
GRUNDY AND SOUTHERN WILL. LOW-LEVEL INSTABILITY DECREASES  
FARTHER TO THE EAST (AS WELL AS DIURNALLY), BUT WE'LL HAVE TO  
KEEP AN EYE ON TRENDS IN THESE AREAS INTO THE NIGHT.  
 
RATZER  
 

 
   
DISCUSSION
 
 
ISSUED AT 247 PM CDT THU JUL 10 2025  
 
THROUGH FRIDAY NIGHT:  
 
SEVERAL ROUNDS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED TO IMPACT  
AT LEAST PORTIONS OF THE AREA LATE THIS AFTERNOON THROUGH FRIDAY  
EVENING. WITH THESE STORMS, THE PRIMARY CONCERNS WILL BE THE  
THREAT FOR STRONG TO POTENTIAL SEVERE STORMS, ALONG WITH VERY  
HEAVY RAINFALL AND POSSIBLE FLASH FLOODING.  
 
AN MCV CONTINUES TO BE NOTED IN SATELLITE IMAGERY SHIFTING OVER  
SOUTHEASTERN MN, WITH AN ASSOCIATED WARM AIR ADVECTION WING NOTED  
EXTENDING SOUTHWARD ALONG THE MISSISSIPPI INTO NORTHWESTERN IL AT  
THE TIME OF THIS WRITING. TO THE EAST, A VERY WARM AND MOIST LOW-  
LEVEL AIRMASS (LOW 70S SURFACE DEWPOINTS) CONTINUES TO  
DESTABILIZE ACROSS NORTHERN IL EARLY THIS AFTERNOON, AND HAS  
RECENTLY SUPPORTED THE DEVELOPMENT OF A FEW ISOLATED SHOWERS AND  
STORMS ACROSS SOUTHERN LIVINGSTON AND FORD COUNTIES IN IL. WE  
EXPECT THUNDERSTORM COVERAGE TO BE ON THE INCREASE THROUGH THE  
REMAINDER OF THE AFTERNOON, WITH AT LEAST SCATTERED COVERAGE  
(40-60%) ANTICIPATED OVER NORTHERN IL INTO EARLY THIS EVENING AS  
THE WARM AIR ADVECTION WING NEAR THE MISSISSIPPI CONTINUES TO  
SLIDE EASTWARD INTO NORTHERN IL.  
 
LOW TO MID-LEVEL FLOW IS INCREASING THIS AFTERNOON (~30 KT) ACROSS  
THE CORN BELT ALONG THE SOUTHERN PERIPHERY OF THE SOUTHEASTERN MN  
MCV AND OVERTOP OF BACKED SOUTHEASTERLY NEAR SURFACE FLOW. THIS IS  
RESULTING IN AMPLE SHEAR THAT WILL BE SUPPORTIVE OF ORGANIZED  
STORMS LATE THIS AFTERNOON INTO THIS EVENING, POSSIBLY INCLUDING  
SOME SUPERCELLS. AS SUCH, A LOW TORNADO AND DAMAGING WIND THREAT  
EXISTS (LEVEL 1 OF 5) WITH THESE STORMS INTO THIS EVENING.  
OUTSIDE OF THE SEVERE THREAT, A HIGH THETA E AIRMASS (WITH  
PRECIPITABLE WATER VALUES OF 1.75"+) WILL ALSO BE SUPPORTIVE OF  
TORRENTIAL DOWNPOURS WITH THESE STORMS.  
 
ADDITIONAL THUNDERSTORMS ARE LIKELY LATER THIS EVENING AND  
TONIGHT AS THE PARENT MCV SHIFTS INTO SOUTHERN WI. THIS IS LIKELY  
TO PROMOTE WAVES OF BACKBUILDING AND TRAINING EAST-SOUTHEASTWARD  
STORMS OVER THE SAME AREAS OF SOUTHERN WI AND/OR NORTHERN IL  
OVERNIGHT. GIVEN THE PRESENCE OF DEEP RICH MOISTURE (PRECIPITABLE  
WATER VALUES 1.8"+), THERE IS INCREASING CONCERN THAT EXCESSIVE  
RAINFALL AMOUNTS (2-3"+) COULD FALL ACROSS PARTS OF NORTHERN IL  
TONIGHT AND POTENTIALLY RESULT IN FLASH FLOODING. FLASH FLOODING  
WOULD PARTICULARLY BE OF CONCERN IF THE HEAVIEST RAINFALL IS  
CONCENTRATED OVER THE CHICAGO AND/OR ROCKFORD METRO AREAS. WE  
GAVE STRONG CONSIDERATION TO ISSUING A FLOOD WATCH FOR PORTIONS  
OF NORTHERN IL (NORTH OF I-80) GIVEN THIS POTENTIAL, BUT WITH  
SOME UNCERTAINTY IN WHICH AREAS ARE MOST AT RISK, WE OPTED TO  
HOLD OFF AT THIS TIME TO ALLOW THE EVENING SHIFT TO GET A BETTER  
HANDLE OF OBSERVATIONAL TRENDS GOING INTO THE EVENING. FOR NOW,  
WE PLAN TO HIGHLIGHT THIS THREAT IN OUR FORECAST GRAPHICS AND  
IN AN ESF.  
 
WHILE SOME SHOWERS AND STORMS COULD LINGER INTO FRIDAY MORNING, IT  
DOES LOOK LIKE THERE WILL BE A SEVERAL HOUR BREAK IN THE ACTIVITY  
IN THE MORNING AND EARLY AFTERNOON. HOWEVER, ADDITIONAL SHOWERS  
THUNDERSTORMS APPEAR LIKELY TO REDEVELOP FRIDAY AFTERNOON AND  
EVENING ALONG THE REMNANT OUTFLOW BOUNDARY FROM TONIGHT'S  
ACTIVITY. THIS ACTIVITY WILL ONCE AGAIN BE DEVELOPING WITHIN A  
WELL SHEARED AND UNSTABLE ENVIRONMENT WHICH WILL SUPPORT  
ORGANIZED AND POTENTIALLY SEVERE STORMS. ADDITIONAL INSTANCES OF  
HEAVY RAINFALL AND POSSIBLE FLASH FLOODING WILL ALSO BE OF CONCERN  
WITH THIS ACTIVITY INTO FRIDAY EVENING.  
 
KJB  
 
SATURDAY THROUGH THURSDAY:  
 
ANOTHER ROUND OF STRONG TO SEVERE THUNDERSTORMS (AND LOCALIZED  
FLASH FLOODING) APPEARS QUITE POSSIBLE SATURDAY AFTERNOON,  
PARTICULARLY FOR AREAS EAST OF I-39. THERE MAY BE A FAIRLY EARLY  
END TO THE STORMS, WITH AN INCREASING POTENTIAL FOR THE  
FOOTPRINT OF ONGOING STORMS TOWARDS/AROUND SUNSET TO BE  
PRIMARILY SOUTHEAST OF I-55 AND PERHAPS EVEN FARTHER SOUTHEAST.  
 
THERE ARE A FEW NOTEWORTHY MESOSCALE WILDCARDS/UNKNOWNS THAT WILL  
UNDOUBTEDLY MODULATE THE PM THUNDERSTORM FORECAST AND ASSOCIATED  
STRONG TO SEVERE T-STORM THREAT. THE FIRST OF THESE, AS IS VERY  
COMMON, IS THE EXTENT OF CONVECTION LINGERING INTO SATURDAY  
MORNING. DETERMINISTIC GUIDANCE IS EXTREMELY MIXED ON THIS ASPECT,  
WITH A WIDE RANGE OF PLAUSIBLE OUTCOMES.  
 
ON ONE END OF THE SPECTRUM, AN EXTENSIVE ROBUST CONVECTIVE  
FOOTPRINT (WITH ASSOCIATED HEAVY RAIN/FLASH FLOOD/LOCALIZED  
SEVERE THREATS) COULD PLAUSIBLY LINGER THROUGH EARLY TO MID  
MORNING SATURDAY. THE STABILIZING COLD POOL FROM THIS MAY THEN  
SERVE TO LIMIT AFTERNOON THUNDERSTORM COVERAGE AND INTENSITY,  
ESPECIALLY WITH NORTHWESTWARD EXTENT. THERE'S LIKELY EVEN A  
PLAUSIBLE SCENARIO IN WHICH THE AFTERNOON "ZONE OF CONCERN"  
SHIFTS WELL SOUTHEAST OF I-55 OR SO. THEN ON THE OTHER END OF  
THE SPECTRUM, IF SHOWER/STORM COVERAGE IS AT A MINIMUM THROUGH  
MOST OF SATURDAY MORNING, THAT WOULD INCREASE THE LIKELIHOOD OF  
MORE WIDESPREAD AFTERNOON STORMS WITH A DAMAGING WIND THREAT FOR  
A LARGER CHUNK OF THE CWA (MORE ON THIS A FEW PARAGRAPHS DOWN).  
 
SYNOPTICALLY SPEAKING ON SATURDAY, MID-LEVEL SHORT-WAVES EMBEDDED  
IN A TROUGH AXIS EXTENDING BACK TO NORTHWEST ONTARIO WILL BE  
ACCOMPANIED AT THE SURFACE BY A WEAK SURFACE LOW AND COLD FRONT  
PROGRESSING ACROSS THE REGION THROUGH SATURDAY EVENING. THE FRONT  
WILL ENCOUNTER A VERY WARM (HIGHS ~84-90F) AND MOIST (EXACTLY HOW  
UNSTABLE TBD) AIR MASS WITH DEW POINTS WELL INTO THE 70S. A FINAL  
PIECE OF THE PUZZLE IS THE TIMING OF THE COLD FRONTAL APPROACH AND  
PASSAGE, WHICH WILL ALSO IN ALL LIKELIHOOD BE MODULATED BY THE  
MORNING UNKNOWNS. OPERATIONAL GUIDANCE HAS OVERALL TRENDED A BIT  
FASTER WITH THE INCOMING COLD FRONT, WHICH COULD VEER WINDS  
EARLIER, REDUCE BOUNDARY LAYER CONVERGENCE, AND LIMIT STORM  
COVERAGE, PARTICULARLY FROM THE I-39 CORRIDOR AND WEST. WHILE THE  
ENSEMBLE SIGNAL FOR ~60-70% POPS/COVERAGE IS STRONG ENOUGH TO  
MAINTAIN THOSE POPS AREA-WIDE IN THE AFTERNOON, ROBUST CONVECTIVE  
INITIATION MAY FAVOR THE EASTERN OR SOUTHEASTERN HALF OF THE CWA.  
THUNDERSTORM CHANCES INTO THE EARLY EVENING, LIKELY FOCUSED  
PRIMARILY SOUTHEAST OF I-55 (AND POSSIBLY ONLY OVER OUR FAR  
SOUTHEAST CWA) WILL THEN QUICKLY COME TO AN END BEHIND THE FRONT.  
 
REGARDING THE SEVERE THREAT, DEEP LAYER SHEAR IS FORECAST TO BE  
SOMEWHAT MUTED (20-30 KT), WHICH WOULD LIMIT THE CHANCE FOR  
WIDESPREAD INTENSE/ORGANIZED STORMS. THAT SAID, 20+ KT OF SHEAR  
PLUS STEEP LOW-LEVEL LAPSE RATES/MODERATE TO HIGH DCAPE AND PRECIP  
LOADING IN DOWNDRAFTS ARE INGREDIENTS THAT MAY YIELD AT LEAST  
LOCALIZED CORRIDORS OF WIND DAMAGE, ESPECIALLY IF SMALL FORWARD  
PROPAGATING SEGMENTS CAN DEVELOP. GIVEN THE OVERALL UNCERTAINTY IN  
THE SETUP AND STORM INTENSITY LIMITING FACTOR, SPC'S THREAT LEVEL  
1 OF 5 (MARGINAL RISK) IN THE DAY 3 OUTLOOK UPDATE APPEARS QUITE  
REASONABLE.  
 
SATURDAY EVENING'S COLD FRONT SHOULD PUSH FAR ENOUGH SOUTHEAST  
INTO SUNDAY, ALONG WITH VERY DRY MID-LEVEL AIR AND NEUTRAL TO  
POSITIVE MID-LEVEL HEIGHT TENDENCIES, TO RESULT IN A MOSTLY (IF  
NOT ENTIRELY) DRY AND LESS HUMID PERIOD AT LEAST THROUGH TUESDAY  
MORNING. THE 12Z NAM WAS REGARDED TO BE AN UNREALISTIC OUTLIER  
WITH ADDITIONAL SHOWERS AND STORMS LATER SATURDAY NIGHT INTO  
SUNDAY. THUNDERSTORM CHANCES MAY THEN AGAIN UPTICK MIDWEEK WITH  
THE NEXT SHORT-WAVE TROUGH AND ACCOMPANYING COLD FRONT. TEMPS  
WILL CONTINUE TO AVERAGE SOLIDLY ABOVE NORMAL WITH MODERATELY  
HUMID TO MUGGY CONDITIONS COMMON TO MID JULY, AND THEN POSSIBLY  
COOL TO BELOW NORMAL BY THE END OF THE WORK WEEK IN THE WAKE OF  
THE COLD FRONT PASSAGE.  
 
CASTRO  
 

 
   
AVIATION /06Z TAFS THROUGH 12Z SATURDAY/
 
 
ISSUED AT 1205 AM CDT FRI JUL 11 2025  
 
SHRA/TSRA SHOULD MOVE EAST OF OUR EASTERN TERMINALS WITHIN THE  
FIRST COUPLE HOURS OF THIS TAF CYCLE WITH STORMS SETTING UP WELL  
SOUTH OF THE TERMINALS THE REST OF TONIGHT. ANOTHER DISTURBANCE  
OVER WESTERN IA IS EXPECTED TO CONTINUE EASTWARD THROUGH THE  
MORNING HOURS AND WE WILL NEED TO MONITOR TREND FOR POSSIBLE  
INCLUSION OF SHRA AND POSSIBLY A TSRA THREAT LATE  
MORNING/MIDDAY. CONFIDENCE IS TOO LOW FOR INCLUDING IN THE TAFS  
YET, BUT WILL CONTINUE TO MONITOR TRENDS.  
 
BETTER THREAT OF SHRA/TSRA IS EXPECTED TO DEVELOP DURING THE  
MID-LATE AFTERNOON HOURS CLOSER TO THE MS RIVER. THIS ACTIVITY  
COULD ORGANIZE INTO A LINE AND PUSH EASTWARD AFFECTING THE  
TERMINALS LATE FRIDAY AFTERNOON OR FRIDAY EVENING. DIDN'T MAKE  
ANY CHANGES TO THE INHERITED TIMING OF THE TEMPO, BUT AS TRENDS  
BECOME CLEARER, SOME ADJUSTMENTS TO TIMING AND POSSIBLE UPGRADE  
TO A TEMPO COULD BE NEEDED.  
 
IN THE WAKE OF HE CURRENT STORMS WINDS SHOULD BECOME LIGHT AND  
TEND TO FAVOR EAST OR SOUTHEAST THIS MORNING. MOST GUIDANCE  
WANTS TO SURGE WARM FRONT NORTHWARD AND RESULT IN WIND SHIFT TO  
SOUTH-SOUTHWESTERLY EARLY THIS MORNING. GIVEN THE COVERAGE OF  
STORMS TO THE SOUTH, HAVE DELAYED THAT WIND SHIFT TIMING IN THE  
TAFS A FEW HOURS AS THESE STORMS SHOULD TEND TO KEEP THE FRONT  
FROM SURGING NORTH OVERNIGHT.  
 
FINALLY, THERE IS A SMALL BREAK IN THE MID-HIGH LEVEL CLOUDINESS  
BETWEEN STORM CLUSTERS THAT COULD RESULT IN A PERIOD OF CLEARING  
PRIOR TO SUNRISE. IF SKIES DO CLEAR OUT, CAN'T RULE OUT SOME IFR  
OR LOW END MVFR CIGS DEVELOPING FOR A SHORT TIME THIS MORNING.  
CONFIDENCE IS TOO LOW TO INCLUDE ANYTHING AT THIS TIME AND WILL  
ALSO BE MONITORING THESE TRENDS THIS MORNING.  
 
- IZZI  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...FLOOD WATCH UNTIL 7 AM CDT FRIDAY FOR ILZ003-ILZ004-ILZ005-  
ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-  
ILZ021-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.  
 
IN...NONE.  
LM...NONE.  
 

 
 

 
 
VISIT US AT WEATHER.GOV/CHICAGO  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab IL Page
The Nexlab IN Page Main Text Page