782  
FXUS63 KLOT 301759  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
1259 PM CDT MON JUN 30 2025  
   
KEY MESSAGES
 
 
- THUNDERSTORM THREAT LATE THIS AFTERNOON THROUGH THE EVENING.  
THE STRONGEST STORMS WILL BE CAPABLE OF LOCALIZED DAMAGING  
WINDS AND HEAVY RAINFALL AND AN ISOLATED FLOOD THREAT.  
 
- HOT WEATHER FOR 4TH OF JULY FESTIVITIES THURSDAY-SUNDAY, WITH  
INCREASING HUMIDITY AND PERIODIC THUNDERSTORM CHANCES,  
ESPECIALLY OVER THE WEEKEND.  
 

 
   
UPDATE
 
 
ISSUED AT 1125 AM CDT MON JUN 30 2025  
 
THE PRIMARY FORECAST CONCERNS TODAY INTO THIS EVENING CONTINUES  
TO FOCUS ON THE THREAT AND COVERAGE OF THUNDERSTORMS. IN THE  
NEAR TERM, A SURFACE BOUNDARY IS NOTED AS OF THIS WRITING  
EXTENDING FROM NEAR ORD, SOUTHWESTWARD INTO NORTHERN LA SALLE  
AND KENDALL COUNTIES. A VERY MOIST PREFRONTAL AIRMASS (DEW  
POINTS IN THE LOWER 70S) HAS FOSTERED SOME RECENT ATTEMPTS AT  
CONVECTIVE INITIATION NEAR THIS BOUNDARY, PARTICULARLY OVER  
CHICAGO. HOWEVER, SOME RESIDUAL CAPPING HAS KEPT THESE ATTEMPTS  
SHORT LIVED OVER THE METRO. WHILE A FEW BRIEF ISOLATED SHOWERS  
AND STORMS WILL CONTINUE TO BE POSSIBLE WITH THIS BOUNDARY FOR  
THE NEXT COUPLE HOURS SOUTHEAST OF I-55, IT APPEARS AN AREA OF  
SUBSIDENCE AND A SLIGHTLY DRIER LOW-LEVEL AIRMASS MOVING INTO  
NORTHERN IL WILL KEEP THE CHANCES OF STORMS UNDER 15% IN THE  
WAKE OF THIS SURFACE BOUNDARY (NORTHWEST OF I-55 AND INLAND FROM  
THE LAKE) THROUGH AT LEAST 2 TO 3 PM THIS AFTERNOON.  
 
THE MAIN WEATHER FEATURE TO WATCH FOR POTENTIALLY DRIVING MORE  
SCATTERED STORM DEVELOPMENT OVER PORTIONS OF OUR AREA LATER THIS  
AFTERNOON (AFTER 3 PM) INTO THIS EVENING IS THE ROBUST MID-LEVEL  
SHORT WAVE TROUGH (AND AN ASSOCIATED MID AND UPPER LEVEL SPEED  
MAX) CURRENTLY DROPPING SOUTHEASTWARD INTO THE UPPER MIDWEST. THIS  
FEATURE IS SLATED TO SWING INTO SOUTHERN WI AND NORTHERN IL  
INTO THIS EVENING. ALSO OF NOTE, IS A REMNANT MCV DISTURBANCE  
SHIFTING EASTWARD ACROSS THE SOUTHEAST IA AND NORTHEAST MO STATE  
LINE. THIS FEATURE IN COMBINATION WITH THE APPROACHING LARGER  
SCALE TROUGH LOOKS TO OFFER THE BEST POTENTIAL (40-50% CHANCE)  
FOR SOME STORMS LATE THIS AFTERNOON AND EVENING. HOWEVER,  
CONFIDENCE IN THE COVERAGE OF STORMS CONTINUES TO BE LOW,  
PARTICULARLY ALONG AND NORTH OF I-80 OWING TO LINGERING  
QUESTIONS ON THE MAGNITUDE OF LOWER-LEVEL CONVERGENCE. IT  
REMAINS POSSIBLE THE THE BETTER COVERAGE OF STORMS LATER TODAY  
INTO THIS EVENING LARGELY REMAINS SOUTH OF I-80. NEVERTHELESS,  
WE WILL CONTINUE WITH 30-50% CHANCES FOR SHOWERS AND  
THUNDERSTORMS THIS AFTERNOON AND EVENING, WITH THE BEST CHANCES  
LOOKING TO BE IN THE 4 PM TO 10 PM TIMEFRAME MENTIONED  
PREVIOUSLY. INCREASING MID AND UPPER-LEVEL FLOW DURING THIS  
PERIOD WITH THE APPROACHING MID-LEVEL TROUGH COULD ALSO SUPPORT  
A FEW STRONGER STORMS.  
 
KJB  
 

 
   
DISCUSSION
 
 
ISSUED AT 303 AM CDT MON JUN 30 2025  
 
THROUGH TUESDAY:  
 
FAIRLY COMPLEX AND LOWER-CONFIDENCE FORECAST FOR TODAY, WITH  
GENERALLY LIMITED LARGE SCALE FORCING MECHANISMS (AT LEAST UNTIL  
LATE IN THE AFTERNOON) BUT WITH SEVERAL MESO-ALPHA SCALE SURFACE  
BOUNDARIES ON WHICH TO FORCE STORMS LATER THIS MORNING AND  
AFTERNOON. THERE IS SOME POTENTIAL FOR MORE ORGANIZED STRONG-  
SEVERE CONVECTION VERY LATE THIS AFTERNOON AND EVENING AS A  
ROBUST SHORTWAVE TROUGH PRESSES THROUGH, BUT THIS STILL ISN'T  
NECESSARILY A "LOCK" YET.  
 
NIGHTTIME MICROPHYSICS RGB IMAGERY REVEALS MID-LEVEL STRATUS  
ALONG AND EAST OF ABOUT I-55, WITHIN A CORRIDOR OF ENHANCED LOW  
TO MID-LEVEL MOISTURE. MODEST ISENTROPIC ASCENT WITHIN THIS  
REGION MAY YIELD SOME INTERMITTENT SHOWERS/STORMS EARLY THIS  
MORNING, WITH THE FOCUS EVENTUALLY SHIFTING EAST OF THE REGION  
THROUGH DAYBREAK.  
 
WHILE A SUBTLE OUTFLOW BOUNDARY (EXHAUSTED FROM EARLIER STORMS  
IN SOUTHERN WISCONSIN) HAS SETTLED NEAR TO JUST NORTH OF I-80,  
FORECAST GUIDANCE SUGGESTS THAT THE LOW-LEVEL WIND FIELD WILL  
HOMOGENIZE THIS MORNING WITH MIXING AS A BROAD SURFACE TROUGH  
SHIFTS ACROSS THE REGION. THIS MAY END UP GENERALLY LIMITING  
SURFACE CONVERGENCE, AND WITH NEUTRAL MID-LEVEL HEIGHT  
TENDENCIES PERSISTING THROUGH EARLY AFTERNOON, SUGGESTING  
ADDITIONAL STORM COVERAGE COULD END UP REMAINING SOMEWHAT  
SUBDUED THROUGH MIDDAY. THE EXCEPTION TO THIS WILL BE NEAR A  
SHARPENING LAKE BREEZE, AND PERHAPS IN THE VICINITY OF ANY  
LOCALLY ENHANCED CONVERGENCE NEAR THE AFOREMENTIONED OUTFLOW. WE  
CONTINUE TO SUSPECT THAT THE HRRR IS TOO AGGRESSIVELY MIXING  
DEWPOINTS OUT TODAY, WHICH IS LIKELY PLAYING SOME ROLE IN ITS  
MORE LIMITED COVERAGE OF SHOWERS/STORMS, AND WE'RE LARGELY  
DISCOUNTING ITS RECENT SOLUTIONS AS A RESULT. WITH DEWPOINTS  
EXPECTED TO REMAIN AROUND 70, CONVECTIVE TEMPERATURES WILL BE  
REACHED QUICKLY THIS MORNING WITH HEATING, AND THE GENERAL  
EXPECTATION IS FOR SCATTERED SHOWER/STORM DEVELOPMENT TO OCCUR  
THROUGH LATE-MORNING/MIDDAY, FOCUSING ACROSS PARTS OF NE  
ILLINOIS AND NW INDIANA.  
 
THROUGH EARLY AFTERNOON, MID-LEVEL FLOW ISN'T EXPECTED TO BE ALL  
THAT SIGNIFICANT, RESULTING IN LIMITED DEEP LAYER SHEAR. AS A  
RESULT, ANY STORMS THAT DEVELOP DURING THIS PERIOD WILL MAINLY  
BE PULSE/MULTI-CELL CLUSTERS, CARRYING A GUSTY DOWNBURST AND  
LOCALLY HEAVY RAINFALL THREAT.  
 
THROUGH THE AFTERNOON, A ROBUST SHORTWAVE TROUGH WILL BEGIN TO  
SWEEP INTO SOUTHERN WISCONSIN, SHIFTING A MID/UPPER-LEVEL WIND  
MAX INTO NORTHERN ILLINOIS. MODEST (20-40 M/12 HOUR) HEIGHT  
FALLS WILL COINCIDE WITH THE APPROACH OF THIS TROUGH, WITH A  
GRADUAL INCREASE IN OVERALL LARGER-SCALE FORCING. INTERESTINGLY,  
NOT SEEING A UNIVERSAL SIGNAL IN THE GUIDANCE SUITE OF  
INCREASING THUNDERSTORM COVERAGE DURING THIS PERIOD, POTENTIALLY  
DUE TO THE LIMITED NATURE OF NEAR-SURFACE CONVERGENCE, AND  
LOWER/MIXED-OUT DEWPOINTS. THAT SAID, THE POTENTIAL FOR ONE OR  
SEVERAL REMNANT MCVS FROM CONVECTION CURRENTLY DEVELOPING ACROSS  
CENTRAL NEBRASKA TO PIVOT ACROSS SOUTHERN IOWA AS THE MAIN  
SHORTWAVE SHIFTS OVERHEAD LENDS SOME CONCERN FOR HIGHER STORM  
COVERAGE LATE THIS AFTERNOON AND EVENING, ALTHOUGH PERHAPS NOT  
QUITE AS FAR NORTH AS THE 00Z NAMNEST ADVERTISED. CONTINUE WITH  
SCATTERED THUNDERSTORM CHANCES DURING THIS PERIOD, AND THIS WILL  
BE THE MAIN TIME TO WATCH (ROUGHLY 4-10 PM) FOR MORE ORGANIZED  
STRONG-SEVERE CONVECTION IN OUR AREA AS DEEP LAYER SHEAR  
INCREASES. IF THE MID-LEVEL FLOW INCREASES AS MUCH AS THE  
NAMNEST INDICATES, AN EMBEDDED SUPERCELL AND ATTENDANT LARGE  
HAIL THREAT COULD ALSO MATERIALIZE, BUT THIS IS NOT THE MOST  
FAVORED OUTCOME AT THIS POINT.  
 
STORM CHANCES MAY LINGER THROUGH THE LATE EVENING, BUT WILL COME  
TO AN END DURING THE EARLY OVERNIGHT HOURS AS A COLD FRONT  
PUSHES THROUGH. TUESDAY WILL FEATURE MORE SEASONABLE  
TEMPERATURES WITH LOWER HUMIDITY.  
 
CARLAW  
 
TUESDAY NIGHT THROUGH SUNDAY:  
 
LOWER HUMIDITY AND MORE PLEASANT NIGHTTIME CONDITIONS FOR A FEW  
DAYS WILL REVERT RIGHT BACK TO UNCOMFORTABLE HEAT AND HUMIDITY IN  
TIME FOR THE PEAK OF INDEPENDENCE DAY RELATED CELEBRATIONS FRIDAY  
THROUGH THE WEEKEND. AS IS COMMON DURING THE HEART OF SUMMER IN  
HOT, HUMID, AND UNSTABLE PATTERNS, THUNDERSTORM CHANCES WILL ALSO  
INCREASE WITH TIME, ESPECIALLY FRIDAY-SATURDAY, THOUGH EXPECT  
PLENTY OF DRY TIME AS WELL.  
 
FOLLOWING A SEASONABLE AND QUIET TUESDAY NIGHT, DRIER NORTHWEST  
FLOW BUT STILL WARM LOW-LEVEL THERMAL FIELDS (IE. MID-UPPER TEENS  
C AT 850 MB AND LOW-MID 20S C AT 925 MB) WILL RESULT IN A VERY  
WARM TO HOT WEDNESDAY AWAY FROM LAKE BREEZE COOLING. DEW POINTS  
APPEAR POISED TO MIX OUT INTO THE LOW 60S IF NOT LOWER, WHICH WITH  
PLENTY OF SUN SHOULD TRANSLATE TO HIGHS IN THE UPPER 80S TO AROUND  
90F. A LAKE BREEZE SHOULD WORK ONTO THE CHICAGO AND NORTHWEST  
INDIANA SHORE, KEEPING HIGHS IN THE LOWER-MID 80S THERE. WE'RE  
CURRENTLY CARRYING A DRY FORECAST ON WEDNESDAY PM, THOUGH CAN'T  
COMPLETELY RULE OUT (~10% CHANCE) A GUSTY THUNDERSTORM NEAR THE  
LAKE BREEZE CONVERGENCE AXIS, PARTICULARLY IF DEW POINTS ARE HIGH  
ENOUGH ON THE COOL SIDE OF THE BOUNDARY.  
 
THURSDAY WILL BE FAIRLY SIMILAR TO WEDNESDAY, THOUGH LIKELY A  
COUPLE DEGREES WARMER AWAY FROM THE LAKE (SOLIDLY UPPER 80S TO  
LOWER 90S) AND DEW POINTS A TICK HIGHER. DESPITE A FAIRLY PARCHED  
AIR MASS STILL IN PLACE ALOFT AND LIKELY SOME MIXING OUT OF DEW  
POINTS AT PEAK HEATING, ANTICIPATE LITTLE/NO CAPPING AND MODERATE  
INSTABILITY IN THE AFTERNOON. THIS COULD PRESENT A THREAT FOR  
ISOLATED "AIRMASS" THUNDERSTORMS WITH DOWNBURSTS (~20% POPS NEAR  
AND NORTH OF I-80 FOR NOW). THE LAKE BREEZE CONVERGENCE ZONE COULD  
AGAIN BE FAVORED FOCUS AREA, IF CONVECTION INDEED INITIATES. WE'LL  
THEN HAVE TO WATCH FOR NOCTURNAL CONVECTION NEARBY THURSDAY NIGHT  
OR EVEN JUST OUTFLOW EFFECTS FROM CONVECTION TO THE NORTH ON THE  
EDGE OF THE EML PLUME. THIS WILL BE AS PRONOUNCED 500 MB HEIGHT  
RISES EDGE EASTWARD WHILE WE'RE STILL IN NORTHWEST FLOW LOCALLY  
(STEERING FLOW TOWARD SOUTHEAST).  
 
BARRING A PROHIBITIVELY LARGE CONVECTIVE OUTFLOW FOOTPRINT INTO  
FRIDAY, THE 4TH THIS YEAR MAY BE IN THE UPPER ECHELON OF RECENT  
HOT JULY 4THS. IT DOESN'T CURRENTLY LOOK RECORD THREATENING, BUT  
MID 90S ARE A DISTINCT POSSIBILITY AS 590+ DAM 500 MB HEIGHTS  
CREST THE SOUTHWESTERN GREAT LAKES AND MID-MS VALLEY REGION. IF  
MID 90S OCCUR AT ORD AND RFD, IT WOULD BE THE WARMEST 7/4 SINCE  
2012'S RECORD SETTING 102F HIGHS AT BOTH SITES. CONCEPTUALLY, THE  
500 MB SETUP SHOULD LEND ITSELF TO INCREASED CAPPING AND LIMITED  
IF ANY CONVECTIVE CHANCES. HOWEVER, IT'S TOO EARLY TO SAY THIS  
FOR SURE, SO PERIODIC SLIGHT CHANCE POPS FOR THE PM HOURS THROUGH  
THE OVERNIGHT INTO EARLY SATURDAY APPEAR WARRANTED.  
 
THE 500 MB RIDGE WILL REMAIN IN PLACE BUT FLATTEN OUT OVER THE  
WEEKEND, OPENING THE DOOR FOR OCCASIONAL SCATTERED THUNDERSTORM  
CHANCES AND PERHAPS EVEN SEMI-ORGANIZED MCSS. STRONGER LARGE SCALE  
FORCING WILL REMAIN TIED NEAR AND NORTH OF THE CANADIAN BORDER,  
THOUGH ENVISION A MYRIAD OF CONVECTIVELY MODULATED IMPULSES, MCVS,  
ALONG WITH FRONTS FROM NORTHERN STREAM DISTURBANCES COULD ALL  
SERVE AS TRIGGERS FOR BOUTS OF STORMS. MID AND UPPER LEVEL  
WINDS (AND CORRESPONDING DEEP LAYER WIND SHEAR) DON'T CURRENTLY  
LOOK SUPPORTIVE FOR WIDESPREAD ORGANIZED SEVERE STORMS OVER THE  
WEEKEND AND BEYOND, THOUGH HIGH PWAT AND HIGH DCAPE AIR MASSES  
(AS WE'VE SEEN THIS PAST WEEK) CAN COMPENSATE FOR ISOLATED  
SEVERE THREATS. THE HIGH PWATS MAY ALSO TRANSLATE TO PERIODIC  
LOCALIZED FLASH FLOODING EPISODES. IF COVERAGE SATURDAY DAYTIME  
IS LOWER AND/OR CONVECTIVE INITIATION (CI) HOLDS OFF UNTIL AFTER  
PEAK HEATING, HIGHS AGAIN LOOK QUITE TOASTY, INTO THE LOWER-MID  
90S WITH SOME UPSIDE POTENTIAL. TEMPS SUNDAY MAY BE MARGINALLY  
COOLER, BUT THEN THERE'S A STRONGER SIGNAL FOR DEW POINTS TO  
REACH THE LOWER-MID 70S.  
 
IT'S IMPOSSIBLE AT THIS RANGE TO PREDICT ANY OF THE SPECIFIC  
DETAILS ASIDE FROM THE GENERAL PATTERN, SO PLEASE STAY TUNED FOR  
UPDATES THROUGH THE WEEK AS WE ASSESS AND REFINE THE THURSDAY-  
SUNDAY (FIREWORKS FESTIVITIES PRIME TIME) PERIOD.  
 
CASTRO  
 

 
   
AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/
 
 
ISSUED AT 1259 PM CDT MON JUN 30 2025  
 
KEY MESSAGES:  
 
- 30% CHANCE OF TSRA THIS AFTERNOON INTO EARLY EVENING.  
 
- LAKE BREEZE TO TURN WINDS NE AT GYY (~19-20Z), MDW (~21-22Z).  
 
EARLIER CONCERNS OF MIDDAY ISOLATED TO SCATTERED THUNDERSTORM  
DEVELOPMENT ALONG THE LAKE BREEZE HAS YET TO MATERIALIZE EARLY  
THIS AFTERNOON DUE TO LINGERING MID-LEVEL CAPPING. ACCORDINGLY,  
HAVE OPTED TO TREND DOWN ON THE TS MENTION AND SHIFT THE PROB30  
TIMING A BIT LATER, FOCUSING IT DURING THE MID AFTERNOON TO  
EARLY EVENING TIMEFRAME (~20-02Z) WHEN THE APPROACHING COLD  
FRONT PAIRED WITH A REMNANT MCV MOVING TOWARD THE AREA FROM WEST  
CENTRAL IL COULD FOSTER ISOLATED TO WIDELY SCATTERED  
THUNDERSTORM DEVELOPMENT AREAWIDE. TS TIMING AT RFD REMAINS  
EARLIER (~19-23Z) DUE TO CLOSER PROXIMITY TO THE COLD FRONT.  
SHOWERS AND STORMS DECREASE IN COVERAGE BY LATE EVENING (2-3Z)  
AS THE FRONT BEGINS TO EXIT TO THE EAST WITH DRY CONDITIONS  
FORECAST OVERNIGHT THROUGH TUESDAY.  
 
WINDS REMAIN WNW EARLY THIS AFTERNOON AROUND 10-12KT. MEANWHILE  
A LAKE BREEZE IS SLOWLY MAKING INLAND PROGRESS, CURRENTLY  
HUGGING THE ILLINOIS SHORE AND IS EXPECTED TO TURN WINDS NE AT  
GYY AROUND 19-20Z, AND COULD REACH MDW AS EARLY AS 21Z, THOUGH  
CONFIDENCE IN THAT TIMING IS ON THE LOWER SIDE. CAN'T FULLY RULE  
OUT A WIND SHIFT AT ORD BUT THIS WOULD LIKELY REQUIRE STORMS TO  
FORM OVER THE LAKE WITH THE ASSOCIATED OUTFLOW HELPING TO PUSH  
THE LAKE BREEZE FURTHER INLAND.  
 
WINDS RETURN TO A NORTHWEST DIRECTION AREAWIDE THIS EVENING  
BEHIND THE COLD FRONT WITH A LAKE BREEZE EXPECTED TO SWING  
INLAND AGAIN DURING THE AFTERNOON ON TUESDAY, WITH GREATEST  
CONFIDENCE IN IT REACHING MDW. IT MAY REACH ORD TOWARD THE END  
OF THE 30-HR TAF PERIOD, THOUGH OPTED TO HOLD OFF AT THIS RANGE  
DUE TO LOWER CONFIDENCE.  
 
PETR  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...NONE.  
 

 
 

 
 
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