869
FXUS63 KIWX 031018
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
618 AM EDT THU SEP 3 2026
KEY MESSAGES
- HEAT AND HUMIDITY CONTINUE THROUGH WITH PEAK HEAT INDICES
AROUND 100 DEGREES.
- 20-30% CHANCE OF THUNDERSTORMS STARTING LATE THIS AFTERNOON.
THE CHANCE OF STORMS PEAKS OVERNIGHT WHEN DAMAGING WIND GUSTS
AND HAIL ARE POSSIBLE HAZARDS. CONFIDENCE IN SEVERE STORMS
OCCURRING IS MEDIUM.
- REMAINING UNSETTLED WITH OPPORTUNITIES FOR THUNDERSTORMS FRIDAY
AND SATURDAY.
DISCUSSION
ISSUED AT 317 AM EDT THU SEP 3 2026
AN UPPER-LEVEL RIDGE AND STALLED OUT FRONTAL BOUNDARY REMAIN THE
PRIMARY ITEMS OF FOCUS FOR THIS FORECAST PERIOD. HOT AND HUMID AIR
PREVAILS ONCE AGAIN THIS AFTERNOON AS HEAT INDICIES ARE FORECAST TO
BE AROUND 100. THE HEAT ADVISORY WAS EXPANDED TO THE ENTIRE FORECAST
AREA. AN OVERALL ABSENCE OF CONVECTION ACROSS WI AND MI HAVE LIMITED
THE ANTICIPATED CLOUD COVER, THUS, A HOTTER AFTERNOON THAN
ORIGINALLY FORECAST. WE'LL RUN INTO A SIMILAR SITUATION FOR FRIDAY,
WHICH, AS IT STANDS RIGHT NOW, IS HEAT-ADVISORY FREE, BUT MAY NEED
TO BE REEVALUATED BASED ON CONVECTIVE TRENDS.
TURNING NOW TO THOSE PESKY THUNDERSTORM CHANCES; INITIAL 00Z CAM
RUNS REVEALED DREADFUL INITIALIZATION WITH OVER-CONVECTION NOTED IN
IA AND WI AT THE TIME, WHILE STRUGGLING TO HANDLE CONVECTION
ELSEWHERE IN THE PLAINS. THIS WEAKENS ALREADY BATTERED FORECAST
CONFIDENCE IN THIS PATTERN. HOWEVER, SIFTING PAST THE OVER-
CONVECTION, ENSEMBLES AND HOURLY RUNS APPEAR TO BE CONVERGING ON
STORMS DEVELOPING OVER SOUTHERN WI THIS EVENING IN THE VICINITY OF A
STRENGTHENING 500-MB JET AND STALLED FRONT BELOW. TIMING IS MURKY,
BUT "AFTER DARK" APPEARS TO BE A REASONABLE BET LOCALLY. THE OVERALL
SEVERE WEATHER ENVIRONMENT IS FAVORABLE, BUT NOTHING TRULY ALARMING,
WITH AMPLE MUCAPE, BULK SHEAR NEAR 30 KNOTS AND MID-LEVEL LAPSE
RATES NEAR 7 C/KM. DAMAGING WIND GUSTS AND HAIL APPEAR TO BE THE
MOST LIKELY OUTCOME FROM STORM CLUSTERS THAT EMERGE FROM SOUTHERN
WISCONSIN. THIS ACTIVITY MAY PERSIST BEYOND DAYBREAK FRIDAY
DEPENDING ON THE UPSTREAM START TIME.
WITH THE UPPER-LEVEL RIDGE STILL FOLDING OVER OUR AREA FRIDAY AND
SATURDAY, THUNDERSTORM CHANCES PERSIST BUT DETAILS ARE SPARSE OWING
TO THE ANTICIPATED FEEDBACK LOOP DAY-TO-DAY. PERHAPS SOME RELIEF
SUNDAY AND THE START OF MONDAY AS CANADIAN HIGH PRESSURE SEEPING
OVER THE EASTERN GREAT LAKES WORKS TO SUPPRESS THE UPPER-LEVEL RIDGE
WESTWARD FOR A TIME. GUIDANCE IS SPLIT ON HOW THE COMING WEEK
EVOLVES, BUT THE OVERALL UPPER AIR PATTERN TO ME FAVORS A UPPER-
LEVEL RIDGE BECOMING CENTERED OVER THE MID-MISSISSIPPI VALLEY AS A
TROUGH ARRIVES TO THE PACIFIC NORTHWEST. THIS WOULD PROMOTE
CONTINUED HEAT AND STORM CHANCES.
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 614 AM EDT THU SEP 3 2026
AN AREA OF THUNDERSTORMS OVER IOWA AND MINNESOTA WILL BE WORTH
WATCHING TODAY AS, IF THEY SUSTAIN THEMSELVES, -TSRA IS POSSIBLE
PRIOR TO 00Z AT KSBN. LOW CONFIDENCE ON THAT SOLUTION AS GUIDANCE
THIS MORNING HAS BEEN TOO FAST AND TOO STRONG WITH THIS AREA OF
STORMS THUS FAR. INSTEAD, HAVE FAVORED TSRA ARRIVING LATE IN
THE TAF PERIOD AS UPPER-LEVEL SUPPORT AND A CLUSTER OF STORMS
EMERGES FROM SOUTHERN WISCONSIN. IT IS UNCLEAR IF ANY STORMS
PERSIST INTO KFWA, BUT THIS WOULD OCCUR AT THE EXTREME END OF
THIS 12Z TAF PERIOD. MODELS CONTINUE TO FLIP AND FLOP, THUS,
ONLY A PROB30 AT KSBN WITH THIS ISSUANCE.
IWX WATCHES/WARNINGS/ADVISORIES
IN...HEAT ADVISORY UNTIL 8 PM EDT /7 PM CDT/ THIS EVENING FOR
INZ005>009-012>015-017-018-020-022>027-032>034-103-104-
116-203-204-216.
OH...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR OHZ001-002-004-
005-015-016-024-025.
MI...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR MIZ078>081-177-
277.
MARINE...NONE.
DISCUSSION...BROWN
AVIATION...BROWN
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