471
FXUS63 KLOT 130628
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
128 AM CDT THU AUG 13 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 /06Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 128 AM CDT THU AUG 13 2026
KEY MESSAGES:
- FOG AND LOW CEILINGS ARE LIKELY TO BE OBSERVED THIS MORNING,
ESPECIALLY AT RFD, DPA, AND GYY.
- A PERIOD OF RAIN IS LIKELY THIS AFTERNOON WITH A 20-25%
CHANCE FOR AN ISOLATED THUNDERSTORM OR TWO TO OCCUR NEAR THE
TERMINALS.
- A CORRIDOR OF WIDESPREAD SHOWERS AND STORMS WILL SET UP IN THE
REGION THURSDAY NIGHT INTO FRIDAY MORNING, THOUGH MOST OF
THIS ACTIVITY IS FAVORED TO REMAIN SOUTH OF THE TERMINALS.
LIGHT/CALM WINDS AND MOSTLY CLEAR SKIES HAVE ALLOWED FOR FOG TO
START DEVELOPING IN THE AREA EARLY THIS MORNING. INCREASING
CIRRUS COVERAGE OVERNIGHT INTRODUCES UNCERTAINTY TO HOW DENSE
THIS FOG MIGHT GET, BUT IFR OR LOWER VISIBILITIES APPEAR TO BE A
DISTINCT POSSIBILITY, PRIMARILY AT RFD, DPA, AND GYY. LOW
STRATUS COVERAGE MAY ALSO INCREASE OVER THE NEXT FEW HOURS AND
ALSO RESULT IN MVFR OR LOWER CEILINGS BEING OBSERVED AT THE
TERMINALS FOR SOME TIME THIS MORNING.
THE NEXT DISTURBANCE IN THIS VERY ACTIVE WEATHER PATTERN WILL
ARRIVE IN NORTHERN ILLINOIS THIS AFTERNOON. IT APPEARS THAT THE
STRONGER THUNDERSTORM ACTIVITY ASSOCIATED WITH THIS DISTURBANCE
WILL TRACK SAFELY SOUTH OF THE TERMINALS, BUT A PERIOD OF RAIN
IS NEVERTHELESS STILL LIKELY TO OCCUR AS THIS DISTURBANCE PASSES
THROUGH. THERE IS ABOUT A 20-25% CHANCE FOR AN ISOLATED
THUNDERSTORM OR TWO TO DEVELOP ON THE BACK SIDE OF THIS RAIN
SHIELD AND AFFECT THE TERMINALS. THIS IS STILL TOO LOW OF A
CHANCE TO WARRANT A FORMAL TSRA OR VCTS MENTION IN THE TAFS, BUT
IT REMAINS POSSIBLE THAT SUCH A MENTION WILL EVENTUALLY BE
NEEDED AS FORECAST AND OBSERVATIONAL TRENDS BECOME MORE APPARENT.
IN THE WAKE OF THIS DISTURBANCE, SHOWERS AND THUNDERSTORMS ARE
LIKELY TO FIRE ALONG THE NORTHERN PERIPHERY OF AN ELEVATED
INSTABILITY PLUME AND PERSIST INTO FRIDAY. SHOWER AND STORM
COVERAGE ACROSS THIS CORRIDOR IS LIKELY TO BE WIDESPREAD AND
FEATURE TRAINING CONVECTIVE ELEMENTS. WHILE THIS AXIS OF
CONVECTIVE ACTIVITY IS FAVORED TO LARGELY REMAIN FOCUSED SOUTH
OF THE TERMINALS, SOME OF THE ASSOCIATED RAIN MAY EVENTUALLY
LIFT FAR ENOUGH NORTHWARD TO AFFECT THE TERMINALS. IF THIS AXIS
ENDS UP SETTING UP FARTHER NORTH THAN PRESENTLY EXPECTED, THEN
IT IS POSSIBLE THAT THE TERMINALS WILL SEE AN EXTENDED PERIOD OF
STORMS AND TORRENTIAL RAINFALL THURSDAY NIGHT INTO FRIDAY
MORNING, BUT THIS IS NOT THE MOST LIKELY OUTCOME AT THIS TIME.
OGOREK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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