553
FXUS63 KLOT 032007
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
307 PM CDT THU SEP 3 2026
KEY MESSAGES
- ANOTHER HOT AND HUMID DAY IS IN STORE FRIDAY WITH PEAK HEAT
INDEX VALUES OF 100 TO 105F, WARMEST SOUTH OF I-80.
- TORRENTIAL RAIN-PRODUCING STORMS WITH A THREAT FOR FLASH
FLOODING MAY IMPACT FAR NORTHERN ILLINOIS LATE TONIGHT INTO
EARLY FRIDAY MORNING, THOUGH CONFIDENCE IS HIGHER THAT THEY
REMAIN IN WISCONSIN.
- THERE IS ANOTHER CHANCE FOR SHOWERS AND THUNDERSTORMS FRIDAY
EVENING.
- A BREAK IN THE PATTERN WILL ARRIVE BY SUNDAY WITH LOWERING
HUMIDITY VALUES AND TEMPERATURES.
DISCUSSION
ISSUED AT 307 PM CDT THU SEP 3 2026
AN OUTFLOW BOUNDARY HAS PUSHED SOUTH TO THE I-80 CORRIDOR EARLY
THIS AFTERNOON. NORTHERLY FLOW BEHIND THE BOUNDARY HAS
MODERATED TEMPERATURES ACROSS FAR NORTHERN ILLINOIS (PRIMARILY
NORTH OF I-88), ALLOWING FOR THE EARLY CANCELLATION OF HEAT
HEADLINES. WHILE EXTREME HEAT HAS ENDED NORTH OF THE BOUNDARY,
EXPECT CONDITIONS TO REMAIN HUMID THROUGH THIS EVENING.
HEAT HEADLINES REMAIN IN EFFECT SOUTH OF I-80, WHERE AFTERNOON
TEMPERATURES ARE REACHING THE LOW TO MID-90S WITH PEAK HEAT
INDICES AROUND 105. ADDITIONALLY, THE HEAT ADVISORY HAS BEEN
EXTENDED THROUGH FRIDAY FOR AREAS GENERALLY ALONG AND SOUTH OF A
LINE FROM MENDOTA, IL, THROUGH KANKAKEE, IL, AND RENSSELAER,
IN.
THE THREAT FOR ADDITIONAL SHOWERS AND THUNDERSTORMS IN OUR AREA
THE REMAINDER OF THE DAY OVERALL LOOK LOW (20-30%), AND OF LOW
AERIAL COVERAGE, OWING TO NEBULOUS LARGE SCALE FORCING NEAR THE
MID-LEVEL RIDGE AXIS. IF ANY STORMS ARE ABLE TO DEVELOP THIS
AFTERNOON, THEIR FAVORED PLACEMENT WILL BE NEAR THE OUTFLOW
BOUNDARY FROM FAR EAST CENTRAL IL INTO NORTHERN IN. OTHERWISE,
WE ARE LOOKING TO HAVE A DRY BUT MUGGY EVENING.
TONIGHT,AN UPPER-LEVEL SHORT-WAVE TROUGH WILL TRACK FROM THE
NORTHERN PLAINS ACROSS THE UPPER MIDWEST, DRIVING A COMPLEX OF
THUNDERSTORMS ACROSS THE LOWER GREAT LAKES. WHILE THE MAIN
COMPLEX MAY STAY NORTHEAST OF OUR AREA, RENEWED CONVECTION IS
PLAUSIBLE FRIDAY MORNING ALONG ITS SOUTHWESTERN FLANK AS A
SOUTHWESTERLY LOW-LEVEL JET INTERACTS WITH A COMPOSITE OUTFLOW
BOUNDARY. THIS SETUP COULD SUPPORT STORM TRAINING AND A
LOCALIZED FLASH FLOOD THREAT, THOUGH CONFIDENCE REMAINS LOW WITH
THE HIGHEST POTENTIAL NORTH OF OUR AREA. REGARDLESS, THERE IS A
30-50% CHANCE OF SCATTERED SHOWERS AND THUNDERSTORMS ACROSS FAR
NORTHEASTERN IL AND NORTHWEST IN BETWEEN 2 AM AND 10 AM FRIDAY.
FOLLOWING MORNING ACTIVITY, CAPPING SHOULD MAINTAIN DRY
CONDITIONS THROUGH FRIDAY AFTERNOON. WE ARE MONITORING FOR
SCATTERED THUNDERSTORMS DEVELOPING ACROSS SOUTHERN WISCONSIN
LATE FRIDAY AFTERNOON OR EVENING ALONG A COLD FRONT, WHICH WOULD
LIKELY SHIFT SOUTHEAST INTO OUR AREA FRIDAY NIGHT. THE SPC HAS
INCLUDED OUR AREA IN A LEVEL 1 OF 5 SEVERE THREAT DUE TO THE
POTENTIAL FOR LOCALLY STRONG WIND GUSTS.
SURFACE HIGH PRESSURE BUILDING INTO THE GREAT LAKES THIS WEEKEND
WILL END OUR HOT AND HUMID SPELL, AT LEAST FOR A FEW DAYS.
TEMPERATURES WILL TREND TOWARD THE UPPER 70S NEAR THE LAKE TO
THE LOW 80S INLAND BY SUNDAY. A MODERATE TO HIGH SWIM RISK IS
POSSIBLE AT LAKE MICHIGAN BEACHES LATE SATURDAY THROUGH SUNDAY
DUE TO PERSISTENT ONSHORE FLOW AND CHOPPY CONDITIONS.
KJB
AVIATION /18Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 102 PM CDT THU SEP 3 2026
TS N AND E OF THE CHICAGO TERMINALS EARLIER THIS MORNING PUSHED
A ROBUST OUTFLOW BOUNDARY ACROSS NORTHERN ILLINOIS. N/NNW WINDS
GUSTING UP TO AROUND 20 KNOTS WILL GRADUALLY WEAKEN WHILE
STEADILY VEERING THIS AFTERNOON, WITH DIRECTIONS ALREADY
BEGINNING TO FAVOR JUST E OF N AT ORD/MDW. THE MAIN TS POTENTIAL
WILL REMAIN SOUTH OF ALL TERMINALS THIS AFTERNOON, BUT HAVE
MAINTAINED PROB30 TS FOR ANOTHER COUPLE HOURS AS ISOLATED TALLER
SHRA AND PERHAPS A ROGUE TS CANNOT BE RULED OUT OVER NORTHEAST
ILLINOIS.
WINDS WILL CONTINUE TO SLOWLY VEER TONIGHT, LIKELY SETTLING SSW
UNDER 10 KNOTS OVERNIGHT. A MID-LEVEL DISTURBANCE WILL THEN
INDUCE ELEVATED TS ACROSS WISCONSIN AND SOUTHERN LAKE MICHIGAN
TONIGHT. IT IS UNCLEAR HOW FAR SW THE TS WILL EXTEND, SO HAVE
MAINTAINED PROB30 TS ROUGHLY IN THE 12-15Z WINDOW FOR THE
CHICAGO TERMINALS. EVEN IF TS DOES NOT DIRECTLY AFFECT THE
TERMINALS, STRONG OUTFLOW IS EXPECTED TO PRODUCE A NE WIND SHIFT
SOMETIME EARLY TO MID MORNING. LIKE TODAY, WINDS SHOULD THEN
SLOWLY VEER THROUGH THE DAY, AND POSSIBLY SETTLE SSW BY LATE
AFTERNOON.
KLUBER
LOT WATCHES/WARNINGS/ADVISORIES
IL...HEAT ADVISORY UNTIL 9 PM CDT THIS EVENING FOR ILZ010-ILZ020-
ILZ106-ILZ107-ILZ108.
HEAT ADVISORY UNTIL 7 PM CDT FRIDAY FOR ILZ019-ILZ021-ILZ023-
ILZ032-ILZ033-ILZ039.
IN...HEAT ADVISORY UNTIL 9 PM CDT THIS EVENING FOR INZ001-INZ002.
HEAT ADVISORY UNTIL 7 PM CDT /8 PM EDT/ FRIDAY FOR INZ010-
INZ011-INZ019.
LM...NONE.
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