751
FXUS63 KLOT 122011
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
311 PM CDT WED AUG 12 2026
KEY MESSAGES
- FOG POSSIBLE TONIGHT INTO EARLY THURSDAY MORNING, WITH THE
NEXT CHANCE OF SHOWERS AND STORMS LATE THURSDAY MORNING INTO
THE AFTERNOON.
- OUR ACTIVE, STORMY WEATHER PATTERN IS EXPECTED TO PERSIST INTO
THE WEEKEND WITH PERIODIC CHANCES OF SEVERE WEATHER AND HEAVY
RAINFALL WHICH COULD LEAD TO FLOODING.
- A PERIOD OF DRY WEATHER MAY FINALLY ARRIVE EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 311 PM CDT WED AUG 12 2026
A MUCH QUIETER AFTERNOON AND EVENING IS ANTICIPATED ACROSS THE
AREA FOLLOWING THE STABILIZING INFLUENCES OF THIS MORNING'S
ROUND OF SHOWERS AND THUNDERSTORMS. ACCORDINGLY, WE HAVE
CONTINUED THE TREND OF LOWERING POPS THROUGH TONIGHT, WITH DRY
CONDITIONS EXPECTED ACROSS MOST OF THE AREA. OUR MAIN CONCERN
FOR TONIGHT IS THE THREAT FOR FOG DEVELOPMENT, AS A VERY MOIST
LOW-LEVEL AIRMASS NOCTURNALLY COOLS AMIDST LIGHT WINDS. ALSO
CANNOT RULE OUT THE POSSIBILITY FOR SOME OF THE FOG TO BECOME
LOCALLY DENSE INTO EARLY THURSDAY MORNING, PARTICULARLY IN AREAS
THAT BECOME MOSTLY CLEAR.
ON THURSDAY, FORECAST ATTENTION WILL BE FOCUSED ON THE
EVOLUTION OF THE NEXT MCS EXPECTED TO TRACK EASTWARD FROM THE
PLAINS OUT ACROSS THE CORN BELT TONIGHT. ULTIMATELY, THIS MCS IS
EXPECTED TO BEGIN TO CROSS THE MISSISSIPPI RIVER AROUND, OR A
BIT AFTER DAYBREAK ON THURSDAY, THOUGH LIKELY IN A WEAKENING
STATE AS THE PRIMARY INSTABILITY GRADIENT OVER IL LOOKS TO
REMAIN SOUTH OF I-80 THURSDAY MORNING. THIS MAY THUS ACT TO
STEER THE STRONGER STORM POTENTIAL WITH THE MCS FARTHER SOUTH
ACROSS CENTRAL PARTS OF IL LATER IN THE MORNING. IN SPITE OF
THIS, HIGH PRECIPITABLE WATER VALUES (~1.9") AND DEEP WARM CLOUD
DEPTHS WILL SUPPORT LOCALLY HEAVY RAINFALL WITH THIS REMNANT
MCS.
LATER THURSDAY, AND ESPECIALLY THURSDAY NIGHT, A SOUTH-
SOUTHWESTERLY LOW-LEVEL JET IS EXPECTED TO RAMP UP ACROSS THE
MID- MISSISSIPPI VALLEY AND NOSE INTO IA AND PARTITIONS OF
NORTHERN IL. INTERESTINGLY, THIS COULD RESULT IN REGENERATING
SHOWERS AND THUNDERSTORMS ALONG A WEST-NORTHWEST TO EAST-
SOUTHEAST CORRIDOR IN THE WAKE OF THURSDAY MCS. WHERE THIS
OCCURS, A FLASH FLOOD THREAT WOULD BE A BIG CONCERN THURSDAY
NIGHT, ESPECIALLY GIVEN THE STORM MOTION TO FAVOR TRAINING CELLS
OVER THE SAME AREAS. AT THIS TIME, THERE ARE SIGNS THAT THE
BEST POTENTIAL FOR SEVERAL HOURS OF TRAINING STORMS MAY REMAIN
SOUTHWEST OF THE CHICAGO METRO AREA, AND POTENTIALLY EVEN
SOUTHWEST OF OUR AREA ALTOGETHER, BUT THIS WILL NEED TO BE
MONITORED.
UNFORTUNATELY, MEDIUM-RANGE GUIDANCE CONTINUES TO DEPICT OUR
ACTIVE PATTERN REMAINING IN PLACE AND SUPPORTING CONTINUED WAVES
OF SHOWERS AND THUNDERSTORMS ACROSS OUR REGION INTO THE WEEKEND.
FORTUNATELY, THERE DOES APPEAR TO BE SOME DECENT AGREEMENT IN
THE GLOBAL MODELS/ENSEMBLES THAT HIGH PRESSURE EVENTUALLY
SETTLES ACROSS THE WESTERN LAKES REGION BY MONDAY-TUESDAY OF
NEXT WEEK. ONCE THIS OCCURS, IT WILL PUSH OUR STALLED FRONTAL
ZONE TO THE SOUTH AND PROVIDE US WITH A MUCH NEEDED BREAK IN
THIS ACTIVE WEATHER PATTERN.
KJB
AVIATION /18Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 1252 PM CDT WED AUG 12 2026
KEY MESSAGES:
- THREAT OF LOW CIGS AND FOG LATE TONIGHT INTO EARLY THURSDAY
MORNING.
- NEXT CHANCE OF SHOWERS AND STORMS COMES THURSDAY AFTERNOON
INTO THURSDAY NIGHT.
ASIDE FROM A SMALL (<20% CHANCE) FOR A FEW ADDITIONAL SHOWERS
THIS AFTERNOON, IT APPEARS WE ARE DONE WITH PRECIPITATION
THROUGH AT LEAST THURSDAY MORNING. THE MAIN AVIATION WEATHER
FOCUS THUS SHIFTS TO THE THREAT FOR LOW CIGS AND FOG TONIGHT
INTO EARLY THURSDAY MORNING. OVERALL, WE APPEAR TO BE IN GOOD
SETUP FOR FOG DEVELOPMENT THROUGH THE EVENING, AND ESPECIALLY
OVERNIGHT, PARTICULARLY AT RFD, DPA AND GYY. THE MAIN CHANGE FOR
THE 18Z TAFS WAS TO HIT THE VSBYS AND CIGS A BIT HARDER AT
THESE SITES FOR A FEW HOURS INTO EARLY THURSDAY MORNING. WE HAVE
ALSO ADDED IN A MENTION FOR LOWER CIGS AND VSBYS AT ORD AND MDW
LATE TONIGHT. WE CERTAINLY CANNOT RULE OUT THE POSSIBILITY FOR
LOWER CONDITIONS (IFR) DEVELOPING OVER THE MAIN CHICAGO
TERMINALS OVERNIGHT, THOUGH CONFIDENCE WITH THIS IS TOO LOW AT
THIS TIME.
THE LOW CIGS AND VSBYS WILL IMPROVE BY MID MORNING ON THURSDAY.
THEREAFTER, WE WILL BE MONITORING THE EVOLUTION OF THE NEXT WAVE
OF SHOWERS AND THUNDERSTORMS EXPECTED TO SHIFT EASTWARD ACROSS
IA LATE TONIGHT INTO EARLY THURSDAY MORNING. THE REMNANTS OF
SOME OF THIS ACTIVITY COULD ATTEMPT TO SHIFT ACROSS THE AREA
TERMINALS THURSDAY AFTERNOON. THIS MAY THUS RESULT IN OUR NEXT
PERIOD OF SHOWERS AND POSSIBLE STORMS. I OPTED TO OMIT THE
THREAT FOR TS FROM THE TAF AT THIS TIME, AS THE BETTER THREAT
FOR ACTUAL STORMS MAY REMAIN SOUTH OF THE TERMINALS. OTHERWISE,
EXPECT EASTERLY SURFACE WINDS THROUGH THE DAY.
KJB
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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