491  
FXUS63 KLOT 020806  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
306 AM CDT TUE SEP 2 2025  
   
KEY MESSAGES  
 
- PERIOD OF RAIN SHOWERS EXPECTED WITH A STRONG COLD FRONT  
WEDNESDAY AFTERNOON AND EVENING. A FEW EMBEDDED NON-SEVERE  
THUNDERSTORMS ARE ALSO POSSIBLE.  
 
- BELOW TO WELL BELOW NORMAL TEMPERATURES ARE EXPECTED FROM  
THURSDAY THROUGH THIS WEEKEND.  
 
 
   
DISCUSSION  
 
ISSUED AT 306 AM CDT TUE SEP 2 2025  
 
THROUGH WEDNESDAY NIGHT:  
 
FOLLOWING SOME PATCHY EARLY MORNING FOG, ONE MORE QUIET WEATHER  
DAY IS ANTICIPATED ACROSS THE AREA. EXPECT AFTERNOON  
TEMPERATURES TODAY TO BE A COUPLE OF DEGREES WARMER THAN THOSE  
OBSERVED ON MONDAY, WHICH SHOULD GENERALLY RESULT IN INLAND  
READINGS TOPPING OUT AROUND 80 UNDER PARTLY CLOUDY AFTERNOON  
SKIES. HOWEVER, SIMILAR TO THE PAST COUPLE OF DAYS, WEAK  
GRADIENT FLOW WILL FAVOR AN INLAND SHIFTING LAKE BREEZE THAT  
WILL FOSTER SLIGHTLY COOLER CONDITIONS (MID 70S) ALONG THE LAKE  
MICHIGAN SHORE.  
 
WEDNESDAY IS STILL SHAPING UP TO BE OUR DAY OF TRANSITION AS  
THE WELL ADVERTISED LARGE SCALE WEATHER PATTERN SHIFT ACROSS  
NORTH AMERICA SENDS A STRONG SURFACE COLD FRONT ACROSS THE AREA  
THROUGH THE DAY. RAIN CHANCES WILL RAMP UP WITH AND BEHIND THIS  
FRONT BY MID TO LATE MORNING ACROSS NORTHWESTERN PARTS OF IL,  
THEN SPREAD ACROSS THE CHICAGO METRO AREA AND POINTS SOUTH AND  
EAST THROUGH THE AFTERNOON AND EVENING HOURS OF WEDNESDAY BEFORE  
ENDING.  
 
AHEAD OF THE FRONT, DEWPOINTS ACROSS SOUTHERN SECTIONS OF THE  
AREA (MAINLY SOUTH OF I-80) ARE FORECAST TO MIX OUT INTO THE  
LOWER 50S AMIDST AIR TEMPERATURE RISING INTO THE LOWER 80S. THE  
NET RESULT WILL BE LIMITED INSTABILITY WITHIN FAIRLY DEEP  
INVERTED-V PROFILES IN ADVANCE OF THE FRONT. WHILE THE OVERALL  
POOR THERMODYNAMIC ENVIRONMENT WITH AND AHEAD OF THE FRONT IS  
EXPECTED TO CURTAIL THE THREAT OF SEVERE WEATHER, LAPSE RATES  
LOOK SUFFICIENT TO SUPPORT SOME INSTANCES OF CHARGE SEPARATION  
IN THE CLOUDS AND HENCE THE PRESENCE OF ISOLATED TO WIDELY  
SCATTERED THUNDERSTORMS EMBEDDED WITHIN THE LARGER AREA OF  
SHOWERS. THE COVERAGE OF THESE SHOWERS WILL BE RATHER WIDESPREAD  
FOR A SHORT PERIOD WEDNESDAY AFTERNOON INTO EARLY WEDNESDAY  
EVENING, THOUGH THE FAST PACE OF THE FRONT IS EXPECTED TO LIMIT  
TOTAL PRECIPITATION AMOUNTS (GENERALLY AN INCH OR LESS IN MOST  
LOCATIONS).  
 
ROBUST COLD ADVECTION IN THE WAKE OF THE FRONT WILL SHOVE A  
NOTABLY COOLER AIRMASS INTO THE REGION LATE WEDNESDAY NIGHT INTO  
THURSDAY. TEMPERATURES BY EARLY THURSDAY MORNING ARE CURRENTLY  
FORECAST TO FALL INTO THE LOW 40S ACROSS PARTS OF NORTHWEST  
ILLINOIS, WITH MID TO UPPER 40S FAVORED ELSEWHERE.  
 
KJB  
 
THURSDAY THROUGH MONDAY:  
 
IN THE WAKE OF WEDNESDAY'S COLD FRONTAL PASSAGE, AN  
UNSEASONABLY COOL AIR MASS WILL SETTLE INTO THE REGION. EARLY  
MORNING TEMPERATURES IN THE 40S AND LOW 50S ON THURSDAY LOOK TO  
WARM ONLY INTO THE 60S DURING THE AFTERNOON, WHICH FOR MOST  
LOCATIONS, WOULD MAKE THURSDAY THE FIRST DAY TO FEATURE HIGH  
TEMPERATURES COOLER THAN 70F SINCE LATE MAY.  
 
ANOTHER PRONOUNCED UPPER-LEVEL TROUGH PRESENTLY LOCATED OVER  
ALASKA WILL LARGELY RETRACE THE FOOTSTEPS OF THE MID-WEEK POLAR  
TROUGH AND DIVE SOUTHEASTWARD INTO GREAT LAKES LATE THURSDAY  
INTO FRIDAY. THE STRONG DYNAMICS ASSOCIATED WITH THIS  
DISTURBANCE ARE LIKELY TO INDUCE ANOTHER ROUND OF PRECIPITATION  
ACROSS THE MIDWEST AS IT MOVES THROUGH. FOR OUR CWA, THURSDAY  
NIGHT INTO EARLY FRIDAY APPEARS TO BE THE FAVORED TIME FRAME FOR  
THIS PRECIPITATION TO OCCUR, THOUGH DEPENDING ON THE STRENGTH  
AND TRACK OF AN ASSOCIATED SURFACE LOW, IT IS POSSIBLE THAT SOME  
LOCATIONS (PARTICULARLY IN OUR SOUTHERN/SOUTHEASTERN COUNTIES)  
COULD MISS OUT ON THIS ROUND OF PRECIPITATION. A PERIOD OF GUSTY  
WESTERLY WINDS CAN ALSO BE EXPECTED BEHIND A REINFORCING COLD  
FRONT ON FRIDAY. THE MAGNITUDE OF THESE WINDS WILL LIKEWISE BE  
MODULATED BY THE PRECISE EVOLUTION OF THE SURFACE LOW, AS WILL  
FRIDAY'S HIGH TEMPERATURES, WHICH COULD BE A REPEAT OF  
THURSDAY'S TEMPERATURES OR COULD END UP BEING A LITTLE WARMER  
AND CLOSER TO EARLY SEPTEMBER NORMALS, PER THE LATEST ENSEMBLE  
AND AVAILABLE MOS GUIDANCE.  
 
BEHIND THIS REINFORCING DISTURBANCE, SURFACE HIGH PRESSURE  
LOOKS TO SETTLE BACK INTO THE REGION OVER THE WEEKEND, FAVORING  
ANOTHER PERIOD OF DRY CONDITIONS WITH CONTINUED BELOW NORMAL  
(THOUGH GRADUALLY WARMING) TEMPERATURES. ENSEMBLE CONSISTENCY  
REGARDING THE OVERALL SYNOPTIC PATTERN EVOLUTION THEN BREAKS  
DOWN GOING INTO NEXT WEEK, RESULTING IN LOWER-THAN-AVERAGE  
CONFIDENCE IN THE FORECAST BEYOND SUNDAY.  
 
OGOREK  
 
 
   
AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/  
 
ISSUED AT 1232 AM CDT TUE SEP 2 2025  
 
KEY MESSAGES:  
 
- POTENTIAL FOR VISIBILITY REDUCTIONS FROM MIST/FOG THROUGH THE  
EARLY MORNING AT RFD, DPA, AND GYY.  
 
- WIND SHIFT EXPECTED BEHIND LAKE BREEZE TODAY AT GYY, MDW, AND  
ORD.  
 
THE ENDURING PRESENCE OF SURFACE HIGH PRESSURE IN THE REGION  
WILL CONTINUE TO SUPPORT DRY AND LARGELY VFR CONDITIONS WITH  
LIGHT WINDS AT AREA TERMINALS THROUGH THE TAF PERIOD. HOWEVER,  
THE CLEAR SKIES AND CALM WINDS OVERNIGHT WILL LIKELY RESULT IN  
PATCHES OF PRIMARILY SHALLOW FOG DEVELOPING SOMEWHERE IN THE  
AREA THROUGH SUNRISE. RFD, DPA, AND GYY ALL STAND A CHANCE TO  
SEE A BRIEF PERIOD OF VISIBILITY REDUCTIONS FROM THIS PRIOR TO  
MID-MORNING.  
 
A LAKE BREEZE IS EXPECTED TO DEVELOP EARLY THIS AFTERNOON AND  
MARCH INLAND A FEW MILES BEFORE STALLING OUT SOMEWHERE NEAR ORD  
AND MDW. BEHIND THE LAKE BREEZE, EASTERLY TO NORTHEASTERLY WINDS  
OF UP TO AROUND 10 KTS ARE EXPECTED, BUT IF THE LAKE BREEZE  
WERE TO STALL BEFORE FULLY TRAVERSING THE MDW AND ORD AIRFIELDS,  
THEN VARIABLE OR WESTERLY TO WEST-SOUTHWESTERLY WINDS OF AROUND  
5 KTS WOULD BE FAVORED TO PREVAIL INSTEAD.  
 
OGOREK  
 
 
   
LOT WATCHES/WARNINGS/ADVISORIES  
 
IL...NONE.  
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