849  
FXUS63 KLOT 181101  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
601 AM CDT THU SEP 18 2025  
   
KEY MESSAGES  
 
- PATCHY FOG REMAINS POSSIBLE EARLY THIS MORNING.  
 
- WARM AND PRIMARILY DRY CONDITIONS PERSIST THROUGH FRIDAY AFTERNOON.  
 
- PERIODIC CHANCES FOR SHOWERS AND SOME THUNDERSTORMS WILL  
RETURN FRIDAY NIGHT INTO NEXT WEEK, THOUGH THERE WILL CONTINUE  
TO BE PLENTY OF DRY HOURS TOO.  
 
 
   
DISCUSSION  
 
ISSUED AT 355 AM CDT THU SEP 18 2025  
 
THROUGH FRIDAY...  
 
THE RIDGE OF HIGH PRESSURE THAT HAS BROUGHT US THE SUNNY AND  
WARM WEATHER THE PAST SEVERAL DAYS REMAINS OVERHEAD, BUT IS  
STARTING TO BE IMPEDED BY THE BROAD TROUGH (AND ITS ASSOCIATED  
SHORTWAVES) CENTERED OVER THE NORTH-CENTRAL CONUS. THAT SAID,  
OUR TRANQUIL WEATHER SHOULD HOLD THROUGH FRIDAY AFTERNOON AS THE  
RIDGE SLOWLY EXITS TO THE EAST. SO EXPECT A COUPLE MORE WARM  
AFTERNOONS WITH HIGHS IN THE MID TO UPPER 80S INLAND AND MID TO  
UPPER 70S NEAR THE LAKE DUE TO ONSHORE WINDS. IN FACT, THE LAKE  
BREEZE TODAY WILL ACTUALLY BE ADDED BY A BACKDOOR COLD FRONT  
THAT WILL SURGE DOWN THE LAKE THIS AFTERNOON WHICH WILL PUSH  
COOLER TEMPERATURES FURTHER INLAND THIS EVENING ACROSS NORTHEAST  
IL.  
 
HOWEVER, THERE IS A SMALL CHANCE (AROUND 20-25%) FOR SOME  
SCATTERED SHOWERS AND THUNDERSTORMS TO DEVELOP NEAR AND WEST OF  
I-39 FRIDAY AFTERNOON AS THE SHORTWAVE OVER KS EJECTS INTO THE  
MISSISSIPPI RIVER VALLEY. GIVEN THAT FORECAST SOUNDINGS STILL  
SHOW A BIT OF DRY AIR TO CONTEND WITH, SUSPECT MOST AREAS COULD  
STILL REMAIN DRY.  
 
BUT BEFORE ALL OF THIS GETS UNDERWAY THERE IS SOME PATCHY FOG  
TO DEAL WITH FIRST. SIMILAR TO LAST NIGHT, THE COMBINATION OF  
CLEAR SKIES AND LIGHT WINDS HAS ALLOWED TEMPERATURES TO COOL  
NEAR THE DEW POINTS AND GIVE WAY TO SOME PATCHY FOG PARTICULARLY  
IN FAR NORTHEAST IL, THE FOX VALLEY, AND NORTHWEST IN. WHILE  
SOME EXPANSION OF THE FOG IS POSSIBLE PRIOR TO DAYBREAK, SUSPECT  
VISIBILITIES FOR MOST WILL BE IN THE 3-5 MILE RANGE. THOUGH  
LOCALLY DENSER POCKETS OF FOG ARE POSSIBLE ESPECIALLY CLOSER TO  
THE LAKE AND NORTHWEST IN WHERE A RESERVOIR OF HIGHER DEW POINTS  
RESIDES. ANY FOG THAT DOES DEVELOP WILL ERODE BY 8-9 AM THIS  
MORNING.  
 
FRIDAY NIGHT THROUGH WEDNESDAY...  
 
THE AFOREMENTIONED TROUGH AND THE ASSOCIATED DEVELOPING SURFACE  
LOW WILL CONTINUE TO MOVE EAST INTO THE UPPER MIDWEST AND  
NORTHERN GREAT LAKES FRIDAY NIGHT INTO SATURDAY. THIS WILL FORCE  
A FRONTAL BOUNDARY EASTWARD ACROSS NORTHEAST IL AND NORTHWEST  
IN FRIDAY NIGHT WHICH IN TURN WILL PUSH ANY SHOWER/STORMS THAT  
DEVELOP FRIDAY AFTERNOON NEAR I-39 EASTWARD. WHILE THIS FRONT  
WILL ADVECT SOME BETTER MOISTURE INTO THE AREA, THERE IS STILL  
FORECAST TO BE A FAIR AMOUNT OF DRY AIR ACROSS THE EASTERN 1/3RD  
OF THE AREA WHICH MAY LIMIT SHOWER AND THUNDERSTORM COVERAGE,  
PARTICULARLY FOR THE CHICAGO METRO AND NORTHWEST IN. REGARDLESS  
OF THE SHOWER/STORM COVERAGE FRIDAY NIGHT, THE BROAD FORCING  
FROM THE TROUGH JUST TO OUR NORTH AND THE STALLED FRONTAL  
BOUNDARY SHOULD STILL BE SUFFICIENT TO KICKOFF PERIODS OF  
SCATTERED SHOWERS AND THUNDERSTORMS SATURDAY AND AGAIN ON  
SUNDAY. THOUGH, PLENTY OF DRY HOURS CAN BE EXPECTED TOO GIVEN  
THE MORE MODEST INSTABILITY WHICH MAY FOCUS SHOWERS AND STORMS  
MAINLY TO THE AFTERNOON AND EARLY EVENING HOURS.  
 
A MORE AMPLIFIED SHORTWAVE TROUGH IS EXPECTED TO EJECT OUT OF  
THE NORTHERN PLAINS ON MONDAY AND PIVOT ACROSS THE UPPER  
MIDWEST/NORTHERN GREAT LAKES MONDAY NIGHT. ASSOCIATED WITH THIS  
WAVE WILL BE A MORE FORMIDABLE COLD FRONT WHICH IS FORECAST TO  
SWING ACROSS OUR AREA LATE SUNDAY AND THROUGH THE DAY ON MONDAY  
BRINING WITH IT A MUCH BROADER COVERAGE OF SHOWERS AND  
THUNDERSTORMS. AS EXPECTED, RAIN CHANCES FOR THE SUNDAY NIGHT-  
MONDAY TIMEFRAME HAVE CONTINUED TO INCREASE AND LOOK TO BE THE  
HIGHEST OF THE WEEKEND AT 50-70%. THAT SAID, WIND SHEAR VALUES  
AND PWATS THIS WEEKEND THROUGH MONDAY CONTINUE TO LOOK RATHER  
MODEST SO THE THREAT FOR ANY SEVERE WEATHER AND/OR HEAVY  
RAINFALL/FLOODING IS STILL LOW. OUTSIDE OF THE RAIN,  
TEMPERATURES FOR THIS WEEKEND AND MONDAY CONTINUE TO LOOK  
SEASONABLY WARM WITH READINGS IN THE UPPER 70S TO LOWER 80S EACH  
AFTERNOON.  
 
FROM TUESDAY ONWARD, THE FORECAST IS STILL VERY UNCERTAIN.  
WHILE GUIDANCE HAS STARTED TO TREND TOWARDS A BROAD  
TROUGH/CLOSED UPPER LOW PIVOTING INTO THE MID-MISSISSIPPI VALLEY  
TUESDAY INTO WEDNESDAY, THERE CONTINUES TO BE DIFFERENCES ON  
TIMING AND LONGEVITY OF THIS SYSTEM OVER OUR AREA. IF THE  
SHORTER DURATION SOLUTIONS PLAY OUT THEN WE COULD BE LOOKING AT  
ANOTHER GLANCING BLOW OF SHOWERS AND STORMS THROUGH MIDWEEK  
FOLLOWED BY A PERIOD OF DRY WEATHER. HOWEVER, IF THE LONGER  
DURATION SOLUTIONS PAN OUT THEN WE COULD BE LOOKING AT SHOWER  
AND STORM CHANCES HANGING AROUND FOR MUCH OF NEXT WEEK. GIVEN  
THE UNCERTAINLY, SAW NO NEED TO ADJUST THE 20% POPS OFFERED BY  
THE BLENDED FORECAST FOR THIS PERIOD BUT WILL CONTINUE TO  
MONITOR TRENDS OVER THE COMING DAYS. REGARDLESS OF HOW THE RAIN  
PLAYS OUT NEXT WEEK, TEMPERATURES ARE FORECAST TO FAVOR NEAR TO  
SLIGHTLY ABOVE AVERAGE FOR LATE SEPTEMBER DUE TO PERSISTENT  
NORTHWEST FLOW ALOFT.  
 
YACK  
 
 
   
AVIATION /12Z TAFS THROUGH 18Z FRIDAY/  
 
ISSUED AT 600 AM CDT THU SEP 18 2025  
 
A BRIEF DIP IN VSBYS TO NEAR MVFR (BR) WILL REMAIN POSSIBLE AT  
AREA TERMINALS AROUND SUNRISE, OTHERWISE VFR CONDITIONS ARE  
FORECAST THROUGH THE PERIOD.  
 
LIGHT AND VARIABLE WINDS WILL CONTINUE THROUGH THE MORNING  
HOURS WITH A LAKE BREEZE EXPECTED TO PUSH INLAND BY EARLY  
AFTERNOON TURNING WINDS EAST TO NORTHEAST AROUND 5-10 KT.  
 
PETR  
 
 
   
LOT WATCHES/WARNINGS/ADVISORIES  
 
IL...NONE.  
IN...NONE.  
LM...NONE.  
 
 
 
 
 
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