142
FXUS63 KLOT 020726
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
226 AM CDT WED SEP 2 2026
KEY MESSAGES
- TODAY WILL BE ANOTHER HOT AND HUMID DAY WITH HEAT INDICES
AROUND 105F.
- SEVERAL ROUNDS OF THUNDERSTORMS WILL MOVE THROUGH THE GENERAL
AREA THURSDAY THROUGH SATURDAY. SOME OF THESE MAY BE SEVERE.
- A BREAK IN THE HOT AND HUMID PATTERN MAY ARRIVE BY EARLY NEXT
WEEK.
DISCUSSION
ISSUED AT 225 AM CDT WED SEP 2 2026
A LARGE HEAT DOME REMAINS STALLED OVER THE LOWER MISSISSIPPI
RIVER VALLEY SOUTH OF A SLOW-MOVING UPPER-LEVEL LOW CURRENTLY IN
CENTRAL ONTARIO. QUASI-ZONAL FLOW REMAINS IN PLACE BETWEEN BOTH
FEATURES AND ATOP A STATIONARY FRONT ACROSS THE CENTRAL GREAT
LAKES. A SHORT-WAVELENGTH UPPER-LEVEL TROUGH EMBEDDED IN THE
ZONAL FLOW IS CURRENTLY SUPPORTING SEVERAL CLUSTERS OF SHOWERS
AND STORMS ALONG THE STATIONARY FRONT STRETCHING FROM
NORTHWESTERN IOWA THROUGH CENTRAL WISCONSIN. MEANWHILE, SOUTH OF
THE FRONT AND INDEED ACROSS OUR AREA, IT IS A WARM AND MUGGY
NIGHT WITH CURRENT AIR TEMPERATURES IN THE MID TO UPPER 70S (DEW
POINTS IN THE LOW TO MID 70S).
BASED ON THE CONTINUED EAST-NORTHEASTERLY TRAJECTORY OF THE
AFOREMENTIONED SHORTWAVE, CURRENT EXPECTATIONS ARE THAT ALL
CLUSTERS OF SHOWERS AND STORMS ALONG THE STATIONARY FRONT WILL
REMAIN NORTH OF OUR AREA THROUGH THE MORNING HOURS. EVEN IF ANY
OUTFLOW MAKES IT TO NORTHERN ILLINOIS THIS MORNING, IT SHOULD
BE SHALLOW ENOUGH TO ERODE FAIRLY QUICKLY. SO BARRING ANY
UNEXPECTED SOUTHWARD JOGS IN THE THUNDERSTORM CLUSTERS OR
STRONGER SOUTHWARD OUTFLOW PUSHES, TODAY IS SETTING UP TO BE
ANOTHER HOT AND HUMID DAY. COMPARED TO YESTERDAY, MIXING
PROFILES TODAY LOOK A HAIR DEEPER WHICH MAY MODESTLY OFFSET
EVAPOTRANSPIRATIONAL ENHANCEMENT TO DEW POINTS. REGARDLESS, WILL
CONTINUE TO LEAN ON NAM/HRDPS GUIDANCE WHICH SHOWS DEW POINTS
REBOUNDING TO THE MID TO LOCALLY UPPER 70S TODAY. WHEN PAIRED
WITH HIGHS IN THE LOWER 90S, HEAT INDEX VALUES SHOULD APPROACH
105F AGAIN. FOR THIS REASON, DID EXPAND THE INHERITED HEAT
ADVISORY TO ENCOMPASS THE ENTIRE AREA. IF MIXING IS MORE
EFFECTIVE TODAY, SUPPOSE A STRAY SHOWER OR STORM MAY ATTEMPT TO
DEVELOP THIS AFTERNOON THOUGH COVERAGE SHOULD BE ISOLATED AT
BEST.
TONIGHT, THE STATIONARY FRONT WILL BEGIN A SOUTHWARD SAG TOWARD
THE ILLINOIS AND WISCONSIN STATE LINE. BROAD AND LARGELY
UNFOCUSED LOW- LEVEL FLOW ATOP THE FRONT MAY ENCOURAGE THE
DEVELOPMENT OF A SHOWER OR THUNDERSTORM NEAR THE FRONTAL
BOUNDARY AT ANY TIME (NOT UNLIKE WHAT WE SAW THE PAST FEW
NIGHTS), SO WILL CARRY LOW-END (20%) POPS NORTH OF I-88 THROUGH
DAYBREAK. OTHERWISE, TONIGHT IS SETTING UP TO BE A REPEAT OF
EARLY THIS MORNING WITH SEASONABLY WARM OVERNIGHT LOWS AND
CONTINUED MUGGY CONDITIONS.
FORECAST CONFIDENCE LOWERS THURSDAY AND THURSDAY NIGHT.
DETERMINISTIC GUIDANCE SUGGESTS AN UPPER-LEVEL SHORTWAVE WILL
ROUND THE RIDGE TOWARD THE IOWA/WISCONSIN/NORTHERN ILLINOIS
VICINITY TOWARD DAYBREAK ACCOMPANIED BY AN UPTICK IN COVERAGE OF
SHOWERS AND STORMS. PROVIDED THIS OCCURS, AT LEAST SOME
FOOTPRINT OF CLOUD COVER AND COOLER TEMPERATURES WOULD BE
EXPECTED ACROSS OUR AREA LASTING INTO EARLY AFTERNOON.
THEREAFTER, GUIDANCE IS HINTING AT ANOTHER UPPER-LEVEL WAVE
APPROACHING THE GREAT LAKES BY EARLY AFTERNOON WHICH MAY LEAD TO
ANOTHER ROUND OF STORMS IN THE GENERAL REGION LASTING THROUGH
THE EARLY MORNING HOURS OF FRIDAY. IF CONVECTIVE COVERAGE IS
MINIMIZED IN THE MORNING, THE AFTERNOON ROUND COULD END UP
FAIRLY PROBLEMATIC WITH A RESERVOIR OF MOISTURE-LADEN
INSTABILITY AND INCREASING DEEP- LAYER SHEAR TO SUPPORT ALL
MODES OF SEVERE THUNDERSTORMS (INCLUDING A THREAT FOR FLASH
FLOODING). HOWEVER IF THE FOOTPRINT OF MORNING SHOWERS AND
STORMS IS VAST, COULD ALSO ENVISION EVOLUTION OF THUNDERSTORMS
THURSDAY AFTERNOON BEING PRETTY MESSY WITH A LOWER CEILING FOR
INTENSITY. AT THIS POINT, SEE TOO MANY CONDITIONALITIES TO OFFER
MORE THAN BROAD-BRUSHED CHANCE (20 TO 40%) POPS. WILL ALSO HOLD
OFF ON ISSUING ANY NEW HEAT ADVISORY FOR PARTS OF THE AREA
THURSDAY IN FAVOR OF EVALUATING FUTURE MODEL TRENDS IN POTENTIAL
CONVECTIVE COVERAGE.
FRIDAY INTO SATURDAY, ENSEMBLE GUIDANCE SUGGESTS THE UPPER-
LEVEL RIDGE WILL RETROGRADE WESTWARD PLACING THE GREAT LAKES
INTO THE PRECARIOUS UPPER-LEVEL NORTHWEST FLOW REGIME. WITH THE
RESERVOIR OF MOISTURE-LADEN INSTABILITY REMAINING IN PLACE
ACROSS THE GREAT LAKES REGION, CAN EASILY ENVISION SEVERAL MORE
ROUNDS OF (SEVERE) STORMS IN THE GENERAL REGION THROUGH SATURDAY
NIGHT. AT LEAST A BRIEF BREAK IN THE PATTERN (BOTH WITH RESPECT
TO HUMIDITY LEVELS AND TEMPERATURES) IS ANTICIPATED EARLY NEXT
WEEK.
BORCHARDT
AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 1230 AM CDT WED SEP 2 2026
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- BREEZY SOUTHWEST WINDS THIS AFTERNOON
VFR CONDITIONS AND SOUTHWEST WINDS ARE EXPECTED TO PREVAIL
THROUGH THE TAF PERIOD. BUT THERE ARE A COUPLE ITEMS REGARDING
THE WINDS THAT ARE BEING MONITORED AND WORTH MENTIONING.
FIRST, THE HIGHEST CONFIDENCE ITEM, BETTER DIURNAL MIXING ON
WEDNESDAY AFTERNOON SHOULD ALLOW FOR BREEZIER WIND GUSTS AROUND
20 KNOTS TO DEVELOP, BUT THEN EVENTUALLY DIMINISH AROUND AND
AFTER 00Z. SECOND, MODELS ARE SUGGESTING A WEAK LAKE BREEZE
COULD DEVELOP TOMORROW AFTERNOON. GIVEN UNCERTAINTY AND THAT
MODELS DEPICT REMAINING MORE CONFINED TO THE SHORELINE, IT WAS
KEPT OUT OF THE TAF. SPEAKING OF WIND SHIFTS, WHILE THERE IS
HIGHER CONFIDENCE IN SOUTHWEST WINDS PREVAILING, THERE IS
ONGOING STORMS IN WISCONSIN CURRENTLY, AND THEY ARE EXPECTED
AGAIN TOMORROW NIGHT. IF STORMS WERE TO STRENGTHEN AND SEND AN
OUTFLOW SOUTHWARD, IT COULD HAVE A DRAMATIC WIND SHIFT
ASSOCIATED WITH IT. MODEL AGREEMENT WAS A LITTLE BIT MORE
ALIGNED TOMORROW NIGHT THAN THE CURRENT OVERNIGHT, BUT
CONFIDENCE WAS TOO LOW TO ADD TO THE TAF. LASTLY, MODELS AROUND
SUGGESTING A SHORT DURATION LOW LEVEL JET AROUND 30 KNOTS TO
DEVELOP BOTH TONIGHT AND TOMORROW NIGHT. AS SURFACE WINDS BECOME
LIGHT, IF NOT CALM, THERE IS A CHANCE FOR A BRIEF WINDOW OF LOW
LEVEL WIND SHEAR (LLWS) AT AREA TERMINALS, BUT AGAIN CONFIDENCE
WAS TOO LOW FOR FORMAL MENTION IN THE TAF.
DK
LOT WATCHES/WARNINGS/ADVISORIES
IL...HEAT ADVISORY FROM NOON TODAY TO 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.
IN...HEAT ADVISORY FROM NOON CDT /1 PM EDT/ TODAY TO 9 PM CDT /10
PM EDT/ THIS EVENING FOR INZ001-INZ002-INZ010-INZ011-
INZ019.
LM...NONE.
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