354  
FXUS63 KLOT 171110  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
610 AM CDT FRI OCT 17 2025  
   
KEY MESSAGES
 
 
- PERIODS OF SHOWERS AND STORMS ARE EXPECTED STARTING LATE  
TONIGHT AND LASTING THROUGH SUNDAY MORNING AS A FALL STORM  
SYSTEM MOVES THROUGH THE AREA.  
 
- PARTS OF THE AREA MAY PICK UP MUCH-NEEDED SOAKING RAINFALL  
OVER THE WEEKEND. THE HIGHEST RAINFALL TOTALS (1-2+ INCHES)  
ARE CURRENTLY FAVORED TO OCCUR NEAR AND EAST OF INTERSTATE 55.  
 
- A PERIOD OF GUSTY NORTHWEST WINDS (GUSTS OF 30 TO 35 MPH) IS  
EXPECTED ON SUNDAY. ADDITIONAL PERIODS OF BREEZY WINDS ARE  
POSSIBLE ON MONDAY AND TUESDAY AS ANOTHER FALL STORM SYSTEM  
MOVES THROUGH THE REGION.  
 
- TEMPERATURES WILL BE ON A SEE-SAW TODAY THROUGH THE MIDDLE OF  
NEXT WEEK AS THE SERIES OF FALL STORMS MOVES THROUGH THE  
REGION.  
 

 
   
DISCUSSION
 
 
ISSUED AT 357 AM CDT FRI OCT 17 2025  
 
THROUGH SUNDAY:  
 
BREEZY RETURN FLOW ON THE BACKSIDE OF A DEPARTING HIGH PRESSURE  
SYSTEM WILL YIELD AN UNSEASONABLY MILD DAY ACROSS THE AREA TODAY  
WITH HIGH TEMPERATURES RANGING FROM THE MID 70S TO THE LOW 80S,  
WARMEST ACROSS OUR WESTERN COUNTIES AND COOLEST IN OUR EASTERN  
COUNTIES. WEAK ISENTROPIC UPGLIDE MAY END UP GENERATING A FEW  
SPRINKLES OR LIGHT RAIN SHOWERS IN FAR NORTHERN ILLINOIS THIS  
MORNING (PARTICULARLY NEAR THE WISCONSIN STATE LINE), BUT  
OTHERWISE, DRY CONDITIONS SHOULD PREVAIL THROUGH THE DAYTIME  
HOURS.  
 
THINGS WILL GET BUSIER WEATHER-WISE GOING INTO THE WEEKEND,  
HOWEVER, AS A HANDFUL OF UPPER-LEVEL DISTURBANCES ENTER THE  
REGION AND INTERACT WITH ONE ANOTHER. INITIALLY, A COMPACT,  
CLOSED-OFF UPPER LOW PRESENTLY OVER THE DAKOTAS WILL DRIFT OFF  
TOWARDS WESTERN ONTARIO TODAY WHILE AN ASSOCIATED SURFACE LOW  
OCCLUDES AND FOLLOWS SUIT. THE ATTENDANT COLD FRONT/BAROCLINIC  
ZONE EXTENDING TO THE SOUTH OF THE LOW WILL GRADUALLY SHUFFLE ITS  
WAY EASTWARD AND WILL LIKELY REACH NORTHWESTERN ILLINOIS AT SOME  
POINT TONIGHT. A STRENGTHENING LOW-LEVEL JET WILL LIKELY  
INVIGORATE CONVECTION ALONG AND AHEAD OF THE FRONT AS ISENTROPIC  
ASCENT/WARM AIR ADVECTION RAMPS UP COMMENSURATELY, AND THIS  
CONVECTIVE CORRIDOR WILL SLIDE ACROSS OUR FORECAST AREA FROM WEST  
TO EAST BETWEEN ABOUT MIDNIGHT AND MID-MORNING. WHILE MID-LEVEL  
LAPSE RATES WILL BE SOMEWHAT LACKLUSTER, THEY SHOULD BE STEEP  
ENOUGH TO PUSH EQUILIBRIUM LEVELS PAST -20C HEIGHTS AND POSSIBLY  
SUPPORT A FEW NON-SEVERE THUNDERSTORMS WITHIN THE BROADER  
CORRIDOR OF CONVECTIVE SHOWER ACTIVITY.  
 
THERE MAY BE A RELATIVE LULL IN SHOWER ACTIVITY DURING THE LATE  
MORNING AS THE AFOREMENTIONED LOW-LEVEL JET WEAKENS AND THE  
INCREASINGLY ILL-DEFINED FRONTAL ZONE STALLS OUT SOMEWHERE OVER  
THE SOUTHEASTERN HALF OF OUR CWA. HOWEVER, ANOTHER UPTICK IN  
CONVECTIVE COVERAGE ALONG THE FRONTAL ZONE APPEARS LIKELY  
TOMORROW AFTERNOON AS SURFACE TEMPERATURES WARM INTO THE MID 70S  
AND A MORE PRONOUNCED UPPER-LEVEL TROUGH SWOOPS INTO THE  
MIDWEST FROM THE NORTHERN PLAINS, PROVIDING A BOOST TO LARGE-  
SCALE FORCING WHILE ALSO MARKEDLY STEEPENING MID-LEVEL LAPSE  
RATES. INCREASING DEEP-LAYER SHEAR COULD ALLOW FOR SOME DEGREE  
OF ORGANIZATION TO OCCUR WITH THE THUNDERSTORMS THAT DEVELOP IN  
OUR SOUTHEASTERN CWA TOMORROW AFTERNOON, LEADING TO SOME  
POTENTIAL FOR STRONG TO MARGINALLY SEVERE DOWNBURST WINDS AND  
SMALL HAIL WITH THE STRONGEST STORMS.  
 
FORCING FOR ASCENT WILL CONTINUE TO STRENGTHEN GOING INTO  
TOMORROW EVENING AS THE AFOREMENTIONED POTENT NORTHERN STREAM  
UPPER-LEVEL TROUGH ATTEMPTS TO PHASE WITH A WEAKER SOUTHERN  
STREAM SHORTWAVE TROUGH WELL TO OUR SOUTH. A BROAD PRECIPITATION  
SHIELD WILL LIKELY BLOSSOM TO OUR SOUTHWEST IN RESPONSE AND  
LIFT NORTHEASTWARD AS THE MAIN TROUGH STARTS TO ACQUIRE A  
NEGATIVE TILT AND THE NASCENT STAGES OF SURFACE CYCLOGENESIS  
BEGIN TO TAKE SHAPE. VARIANCE ACROSS THE LATEST SUITE OF MODEL  
GUIDANCE REMAINS QUITE LARGE FOR BEING 36-48 HOURS OUT OWING TO  
UNCERTAINTY OVER HOW THE PHASING PROCESS BETWEEN THE TWO UPPER-  
LEVEL DISTURBANCES WILL PLAY OUT, BUT THE MOST LIKELY SOLUTION  
AT THIS TIME INVOLVES THE MAIN PRECIPITATION SHIELD STAYING  
FOCUSED OVER THE SOUTHEASTERN HALF OF OUR FORECAST AREA SATURDAY  
NIGHT INTO SUNDAY MORNING WHILE A SECONDARY BAND OF STRONGLY-  
FORCED PRECIPITATION FORMS ALONG A REINFORCING COLD FRONT  
ASSOCIATED WITH THE NORTHERN STREAM TROUGH AND SWEEPS ACROSS THE  
REMAINDER OF OUR CWA IN TANDEM WITH THE FRONT.  
 
IF THE PHASING PLAYS OUT SOMEWHAT QUICKLY AND CLEANLY, THEN  
STRONG DEFORMATION WITHIN THE MAIN PRECIPITATION SHIELD COULD  
LAY OUT A STRIPE OF 2+" RAINFALL TOTALS SOMEWHERE. IN SUCH A  
SCENARIO, THERE IS A LOWER-END CHANCE THAT SOME MINOR HYDROLOGIC  
CONCERNS ARISE WITHIN THE CORRIDOR OF WHERE HEAVIER RAINFALL  
OCCURS (PARTICULARLY IF THIS HEAVIER RAINFALL ENDS UP OCCURRING  
OVER THE MORE URBANIZED PORTIONS OF THE CHICAGO METRO). HOWEVER,  
THE ANTECEDENT DRYNESS AND THE RELATIVELY LONG DURATION OF THE  
RAINFALL SHOULD OTHERWISE PRECLUDE A MORE APPRECIABLE THREAT FOR  
FLOODING FROM MATERIALIZING.  
 
LASTLY, POST-FRONTAL NORTHWESTERLY WINDS COULD BECOME A BIT  
STRONG ON SUNDAY WITH GUSTS NEARING 40 MPH AT TIMES NOT OUT OF  
THE QUESTION IN A SCENARIO FEATURING A CLEANER PHASING OF THE  
AFOREMENTIONED WAVES AND ASSOCIATED ASSOCIATED STRONGER SURFACE  
CYCLOGENESIS. COLD AIR ADVECTION OFF OF THESE WINDS WILL RESULT IN  
COOLER DAYTIME TEMPERATURES ON SUNDAY WITH MOST LOCATIONS IN OUR  
FORECAST AREA CURRENTLY LOOKING LIKE THEY WON'T BREAK 60 DEGREES.  
THE RAIN SHOULD COME TO END DURING THE DAYTIME ON SUNDAY AS HIGH  
PRESSURE STARTS TO BUILD BACK INTO THE REGION.  
 
OGOREK  
 
SUNDAY NIGHT THROUGH THURSDAY:  
 
THE UPPER-LEVEL PATTERN WILL REMAIN ENERGETIC IN THE WAKE OF  
THE WEEKEND STORM SYSTEM WITH A SECONDARY UPPER-LEVEL TROUGH AND  
ASSOCIATED SURFACE LOW POISED TO DIVE SOUTHEASTWARD INTO THE  
UPPER MIDWEST IN THE MONDAY TO TUESDAY TIMEFRAME. OVER THE PAST  
FEW MODEL CYCLES, ENSEMBLE GUIDANCE HAS TRENDED DEEPER/STRONGER  
WITH THE SECONDARY TROUGH, WITH A GENERAL IDEA OF RAPID  
SECONDARY LOW DEVELOPMENT TAKING PLACE SOMEWHERE IN THE UPPER  
GREAT LAKES.  
 
EVEN WITH THE USUAL VARIANCE IN THE EVOLUTION OF THE LOW  
DEPICTED AMONG GUIDANCE, A SIGNAL IS GROWING FOR A PERIOD OF  
BREEZY SOUTHWEST WINDS ON MONDAY (WAA AHEAD OF THE SYSTEM)  
TRANSITIONING TO BREEZY WEST TO NORTHWEST WINDS ON TUESDAY (CAA  
BEHIND THE SYSTEM). IN SCENARIOS WHERE THE SURFACE LOW IS STRONG  
(SUB 1000MB) AND MOVES/WIGGLES CLOSE TO OUR AREA, IT IS EASY TO  
ENVISION PEAK GUSTS IN EITHER REGIME TAGGING 40 TO 45 MPH, AS  
HINTED BY 40KT OF FLOW AT THE TOP OF THE MIXED LAYER IN  
DETERMINISTIC GFS AND ECMWF FORECAST SOUNDINGS. THIS'LL BE  
SOMETHING TO KEEP AN EYE ON AS WE GET CLOSER. UNLIKE THE STORM  
SYSTEM COMING THROUGH THIS WEEKEND, CHANCES FOR MEANINGFUL  
RAINFALL WITH THE SECONDARY SYSTEM WILL BE RELEGATED TO A  
QUICKILY-MOVING BAND OF SHOWERS ALONG THE SOUTHEASTWARD-SURGING  
COLD FRONT MONDAY EVENING AND PERHAPS A FEW SHOWERS LINGERING  
BEHIND AS THE MID-LEVEL COLD POOL ASSOCIATED WITH THE TROUGH  
SLIDE OVERHEAD.  
 
AFTER A RELATIVELY WARM MONDAY WITH HIGHS IN THE MID 60S,  
TEMPERATURES BEHIND THE FRONT ON TUESDAY WILL BE NOTICEABLY  
COOLER AND IN THE MID TO UPPER 50S. WE'LL HAVE TO WATCH FOR ANY  
EMBEDDED SHORTWAVES TO MOVE OVER THE AREA ALONG THE BACKSIDE OF  
THE UPPER-LEVEL TROUGH TO SUPPORT A DIURNAL FLARE IN SCATTERED  
SHOWERS, AS IS TYPICAL THIS TIME OF YEAR. AS THE SYSTEM PULLS  
AWAY TUESDAY NIGHT, TEMPERATURES WILL BE POISED TO FALL INTO THE  
UPPER 30S TO LOWER 40S AWAY FROM THE LAKE. IN SCENARIOS WHERE  
THE BACKSIDE OF THE CYCLONIC SHEAR AXIS PASSES OVERHEAD  
(ENCOURAGING CLOUDS TO CLEAR) TUESDAY NIGHT, TEMPERATURES  
OVERNIGHT AND INTO WEDNESDAY MORNING MAY MAKE A RUN FOR THE  
FREEZING MARK.  
 
FORECAST CONFIDENCE LOWERS FROM THE MIDDLE OF THE WEEK ONWARD.  
WITH THAT SAID, ENSEMBLE MODEL GUIDANCE IS STARTING TO EXHIBIT A  
SIGNAL FOR YET ANOTHER SYSTEM APPROACHING THE GENERAL AREA  
TOWARD THE END OF THE WORKWEEK.  
 
BORCHARDT  
 

 
   
AVIATION /12Z TAFS THROUGH 18Z SATURDAY/
 
 
ISSUED AT 610 AM CDT FRI OCT 17 2025  
 
A SURFACE HIGH PRESSURE SYSTEM WILL SLOWLY DEPART THE GREAT  
LAKES REGION TODAY AS A SURFACE LOW OVER THE DAKOTAS LIFTS  
NORTHEASTWARD INTO SOUTHERN CANADA. A TRAILING SURFACE FRONT IN  
THE UPPER MIDWEST WILL CAUSE SURFACE TROUGHING TO ENCROACH  
EASTWARD INTO THE GREAT LAKES, FORCING THE LOW-LEVEL PRESSURE  
GRADIENT TO BOTH TIGHTEN AND REORIENT FROM SOUTHWEST TO  
NORTHEAST. AS A RESULT, THE EXPECTATION IS FOR SURFACE WINDS TO  
BECOME DECIDEDLY SOUTHWESTERLY AND INCREASE IN MAGNITUDE WITH  
GUSTS OF 20-25KT WITHIN A FEW HOURS AFTER SUNRISE. A PARCHED  
AIRMASS SHOULD RELEGATE CLOUDS TO THE MID TO UPPER-LEVELS,  
LARGELY ABOVE 10KFT.  
 
TONIGHT, THE SURFACE FRONT WILL SHIFT EASTWARD TOWARD THE  
MISSISSIPPI RIVER IN TANDEM WITH THE EASTWARD SHOVE OF AN  
UPPER-LEVEL SHEAR AXIS. MOST GUIDANCE DEPICTS THE EXCITATION OF  
THE NOCTURNAL LOW-LEVEL JET AHEAD OF BOTH FEATURES, WITH  
925-850MB FLOW PROGGED TO INCREASE TO 35 TO LOCALLY 40KT BY 06Z.  
WITH THE DRY LOW-LEVEL AIRMASS FACILITATING EFFICIENT SURFACE  
DECOUPLING, DO HAVE SOME CONCERN FOR MARGINAL LLWS THRESHOLDS  
BEING MET FOR A FEW HOURS DURING THE OVERNIGHT HOURS. HOWEVER,  
SUSPECT THE TIGHTENING LOW-LEVEL PRESSURE GRADIENT MAY ALLOW  
FOR SURFACE WINDS TO REMAIN JUST ELEVATED ENOUGH (10-13KT OR SO)  
TO LIMIT CRITERIA FROM BEING MET, SO WILL CONTINUE TO WITHHOLD  
A FORMAL MENTION IN THE OUTGOING TAFS.  
 
TOWARD THE END OF THE TAF PERIOD, INCREASING ISENTROPIC ASCENT  
IMMEDIATELY AHEAD OF THE SLOWING SURFACE FRONT SHOULD ALLOW FOR  
WIDELY SCATTERED HIGH-BASED SHOWERS TO DEVELOP NEAR THE  
MISSISSIPPI RIVER AND SPREAD EASTWARD TOWARD/OVER THE TERMINALS  
(LARGELY AFTER 06Z). A QUICK LOOK AT FORECAST SOUNDINGS SHOW  
SKINNY AND LARGELY LOW-CENTROID INSTABILITY PROFILES (MOSTLY UNDER  
THE MINUS 20C LEVEL), SUGGESTING COVERAGE OF THUNDER MAY BE MORE  
ISOLATED THAN WIDESPREAD (CALL IT A 20 TO 30% CHANCE AT ANY  
GIVEN TERMINAL). SO, WILL GO AHEAD AND ADVERTISE PREVAILING  
SHOWERS STARTING JUST BEFORE DAYBREAK.  
 
FINALLY, THERE IS A MODEST SIGNAL THAT CIGS MAY ATTEMPT TO  
BUILD DOWNWARD INTO MVFR TOWARD THE VERY END OF THE 30-HOUR TAF  
WINDOW AT ORD/MDW AS THE FRONTAL ZONE WASHES OUT OVER THE AREA.  
FOR NOW, WILL TUCK IN A SCT018 IN FAVOR OF EVALUATING MODEL  
TRENDS TO INFORM LATER TAF PACKAGES.  
 
BORCHARDT  
 

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

 
 

 
 
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