426
FXUS63 KLOT 012307
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
607 PM CDT TUE SEP 1 2026
KEY MESSAGES
- HOT AND HUMID CONDITIONS WILL PERSIST WITH PEAK AFTERNOON
HEAT INDICES AROUND 100 TO LOCALLY 110F TODAY AND AGAIN ON
WEDNESDAY.
- CHANCES FOR THUNDERSTORMS INCREASE THURSDAY AND FRIDAY AS THE
HOT AND HUMID CONDITIONS ARE PUSHED SOUTH OF I-80.
- A BREAK IN THE HUMIDITY MAY MATERIALIZE THIS WEEKEND.
DISCUSSION
ISSUED AT 202 PM CDT TUE SEP 1 2026
THE BROAD RIDGE OF HIGH PRESSURE OVER THE OHIO AND TENNESSEE
RIVER VALLEYS CONTINUES TO BUILD INTO THE SOUTHERN GREAT LAKES
THIS AFTERNOON. BENEATH THE RIDGE, CLEAR SKIES HAVE ALLOWED
TEMPERATURES TO WARM INTO THE UPPER 80S AND LOWER 90S SO FAR AND
WITH SOME DIURNAL HEATING STILL TO GO HIGHS SHOULD TOP OUT IN
THE MID-90S BEFORE SUNSET. DEW POINTS HAVE ALSO BEEN INCREASING
INTO THE MID-70S COURTESY OF SOME MOIST ADVECTION AND
EVAPOTRANSPIRATION (CORN/CROP SWEAT) WHICH AS TEMPERATURE REACH
THE MID-90S SHOULD RESULT IN PEAK HEAT INDICES AROUND 105F WITH
LOCALIZED READINGS AROUND 110F. THUS, A HEAT ADVISORY REMAINS IN
EFFECT THROUGH 9 PM CDT FOR ALL OF NORTHERN IL AND NORTHWEST
IN.
RIDING ATOP THE AFOREMENTIONED RIDGE IN NORTHERN IA AND
SOUTHERN WI IS A SHORTWAVE DISTURBANCE WHICH HAS LEAD TO THE
DEVELOPMENT OF SOME SCATTERED SHOWERS AND THUNDERSTORMS. WITH
THE BUILDING SUBSIDENCE IN NORTHERN IL, THESE SHOWERS AND STORMS
SHOULD REMAIN NORTH OF THE IL-WI LINE SO EXPECT DRY CONDITIONS
TO PREVAIL LOCALLY THROUGH TONIGHT.
AFTER SUNSET THE LOSS OF DIURNAL HEATING SHOULD ALLOW DEW
POINTS TO TAPER SOME AND ALLOW TEMPERATURES TO DIP INTO THE
LOWER TO MID-70S OVERNIGHT. THIS IN TURN SHOULD ALLOW FOR A
BRIEF PERIOD OF RELIEF TONIGHT BEFORE DIURNAL HEATING COMMENCE
WEDNESDAY MORNING AND RESULTS IN ANOTHER DAY OF HOT AND HUMID
WEATHER. THAT SAID, WITH DRIER AIR FORECAST TO BE OVERHEAD
WEDNESDAY AFTERNOON DEW POINTS MAY ACTUALLY BE A TAD LOWER WITH
THE DEEPER MIXING EXPECTED WHICH IN TURN MAY KEEP PEAK HEAT
INDICES MORE INTO THE 100-105F RANGE. WHILE THESE HEAT INDICES
ARE STILL DANGEROUS, THEY ARE JUST UNDER OFFICIAL CRITERIA FOR
ANOTHER WIDESPREAD HEAT ADVISORY. WITH THE UNCERTAINTY IN DEW
POINTS HAVE OPTED TO MAINTAIN THE HEAT ADVISORY FROM 12-9 PM CDT
WEDNESDAY FOR AREAS SOUTH OF I-80 WHERE HEAT INDICES ARE
FORECAST TO BE THE HIGHEST, BUT IF CONFIDENCE GROWS IN HIGHER
DEW POINTS OCCURRING THEN THIS ADVISORY MAY NEED TO BE EXTENDED
ACROSS THE REST OF THE AREA. REGARDLESS, RAIN CHANCES ON
WEDNESDAY LOOK TO BE VIRTUALLY ZERO GIVEN THE STRONG SUBSIDENCE
AND DRIER MID-LEVELS KEEPING THE ATMOSPHERE CAPPED.
THE RIDGE SHOULD BEGIN TO BREAK DOWN AND SHIFT SOUTH AND EAST
INTO THE MID-ATLANTIC WEDNESDAY NIGHT INTO THURSDAY WHICH WILL
TURN ALLOW THE PARADE OF SHORTWAVES ROUNDING IT'S NORTHERN
PERIPHERY TO DRIFT BACK OVER NORTHERN IL AND NORTHWEST IN. THESE
SHORTWAVES IN COMBINATION WITH THE WARM, HUMID, AND UNSTABLE
AIR MASS OVERHEAD SHOULD RESULT IN AN UPTICK IN SHOWER AND
THUNDERSTORM COVERAGE. WHILE THERE IS A CHANCE THAT THE INITIAL
SHORTWAVE MOVE ACROSS SOUTHERN WI WEDNESDAY NIGHT COULD BRING A
FEW SHOWERS/STORMS TO NORTHERN IL, IT SEEMS THE LINGERING
SUBSIDENCE AND CAPPING MAY KEEP THESE STORMS TO OUR NORTH UNTIL
A SECONDARY SHORTWAVE EJECTS OUT OF THE CENTRAL PLAINS ON
THURSDAY. THEREFORE, THE BETTER COVERAGE OF SHOWERS AND
THUNDERSTORMS LOCALLY LOOKS TO BE THURSDAY AFTERNOON AND EVENING
AS THIS SECONDARY WAVE PIVOTS OVERHEAD. GIVEN THE STEEP LAPSE
RATES, DECENT MUCAPE, AND 40+ KTS OF EFFECTIVE SHEAR, ANY STORMS
THAT DEVELOP ON THURSDAY WILL HAVE THE POTENTIAL TO BECOME
STRONG TO SEVERE. SINCE MOST OF THE INSTABILITY SHOULD BE
ELEVATED IT SEEMS THE MAIN SEVERE HAZARD WILL BE DAMAGING WINDS
AND MAYBE SOME LARGE HAIL, BUT IF STORMS CAN BECOME SURFACE
BASED THERE SHOULD BE SOME DECENT LOW-LEVEL SHEAR IN PLACE TO
GENERATE SOME SUPERCELLS AND POSSIBLY A LOCALIZED TORNADO
THREAT. FOR NOW THE STORM PREDICTION CENTER HAS MAINTAINED THEIR
MARGINAL (LEVEL 1 OF 5) RISK FOR ALL OF NORTHERN IL AND
NORTHWEST IN WHICH SEEMS REASONABLE AT THIS TIME.
HEADING INTO FRIDAY, ANOTHER MID-LEVEL RIDGE IS FORECAST TO
BEGIN TAKING SHAPE OVER THE CENTRAL CONUS WHICH LOOKS TO RESULT
IN THE RETURN OF NORTHWEST FLOW ALOFT OVER THE GREAT LAKES.
WHILE THIS FLOW PATTERN SHOULD HELP TO BREAK UP THE HEAT AND
HUMIDITY A BIT, IT WILL ALSO KEEP CHANCES FOR PERIODIC SHOWERS
AND THUNDERSTORMS AROUND THROUGH AT LEAST THE END OF THE WEEK.
WITH UNCERTAINTY IN GUIDANCE ON HOW FAR EAST THE NEW RIDGE WILL
ESTABLISH, CONFIDENCE IS LOW ON WHERE THE GREATEST COVERAGE OF
SHOWERS AND STORMS FRIDAY ONWARD WILL BE. THAT SAID, IT DOES
LOOK AS IF SOME DRY PERIODS WILL BE POSSIBLE FRIDAY AND THIS
WEEKEND SO MAKE SURE TO KEEP AN EYE ON THE FORECAST IF YOU HAVE
ANY OUTDOOR PLANS. REGARDLESS, TEMPERATURES SHOULD SETTLE INTO
THE MID-80S FOR MUCH OF THE UPCOMING WEEKEND AND WITH LOWER
HUMIDITY KEEPING HEAT INDICES ON PAR WITH THE TEMPERATURES.
THOUGH, THESE READINGS WILL STILL BE ROUGHLY 5-10 DEGREES ABOVE
AVERAGE FOR EARLY SEPTEMBER.
YACK
AVIATION /00Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 607 PM CDT TUE SEP 1 2026
THERE ARE NO KEY CONCERNS TO HIGHLIGHT FOR THE 00Z TAF PERIOD.
SW WINDS BELOW 10 KT THROUGH THE NIGHT WILL GUST TO AROUND 20
KT FOR THE LATE MORNING AND AFTERNOON ON WEDNESDAY BEFORE
SUBSIDING AGAIN FOR THE EVENING. EXPECT VFR THROUGHOUT THE
PERIOD.
DOOM
LOT WATCHES/WARNINGS/ADVISORIES
IL...HEAT ADVISORY UNTIL 9 PM CDT THIS EVENING FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
ILZ105-ILZ106-ILZ107-ILZ108.
HEAT ADVISORY FROM NOON TO 9 PM CDT WEDNESDAY FOR ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ105-ILZ106-
ILZ107-ILZ108.
IN...HEAT ADVISORY UNTIL 9 PM CDT /10 PM EDT/ THIS EVENING FOR
INZ001-INZ002-INZ010-INZ011-INZ019.
HEAT ADVISORY FROM NOON CDT /1 PM EDT/ TO 9 PM CDT /10 PM EDT/
WEDNESDAY FOR INZ001-INZ002-INZ010-INZ011-INZ019.
LM...NONE.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page