612
FXUS63 KIWX 021015
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
615 AM EDT WED SEP 2 2026
KEY MESSAGES
- HEAT AND HUMIDITY CONTINUE WITH PEAK HEAT INDICES AROUND 100
DEGREES TODAY.
- 10% CHANCE OF A STRAY THUNDERSTORM THIS AFTERNOON. 20-40%
CHANCE OF THUNDERSTORMS BEGINNING EARLY THURSDAY MORNING.
STORMS MAY PRODUCE DAMAGING WINDS. LOW CONFIDENCE AT THIS
TIME.
- NOT QUITE AS HOT FRIDAY AND SATURDAY, BUT SHOWER AND STORM
CHANCES PERSIST (30-50% CHANCE).
DISCUSSION
ISSUED AT 242 AM EDT WED SEP 2 2026
THE WELL-ADVERTISED UPPER-LEVEL RIDGE REMAINS THE PRIMARY STORY THIS
MORNING, BRINGING HEAT AND HUMIDITY AND A NON-ZERO CHANCE OF A STRAY
THUNDERSTORM. WATER VAPOR IMAGERY SHOWS THE RIDGE AXIS CRESTING
NORTHERN ILLINOIS AND EVEN FAR SOUTHERN MICHIGAN. UPSTREAM
CONVECTION OVER NORTHERN IA AND SOUTHEAST MN HAS BEEN RATHER CYCLIC
IN ITS INTENSITY ON IR SATELLITE, BUT THE EASTERN EXTEND OF ACTIVITY
IS EXPANDING ACROSS CENTRAL-SOUTHERN LAKE MICHIGAN. GIVEN THE RIDGE
AXIS PLACEMENT, HIGH CONFIDENCE IN DRY CONDITIONS THIS MORNING.
HOWEVER, WHILE I'VE SHIPPED OUT A DRY FORECAST TODAY (10% POP), I
CANNOT COMPLETELY RULE OUT A STRAY THUNDERSTORMS THIS AFTERNOON. THE
PRIMARY FORCING MECHANISM COULD BE A DEPARTING 500-MB JET STREAK,
BUT THIS FOCUSES PRIMARY ACROSS CENTRAL MI AND INTO ONTARIO.
MEANWHILE, A SECOND GROUP OF CAMS SUGGESTS RENEWED, ISOALTED ACTIVITY
ALONG THE IL-IN BORDER IN THE 4P-6P ET WINDOW. THIS MIGHT BE FORCED
BY A LINGERING OUTFLOW/MCV FROM THE AFORMENTIONED UPSTREAM ACTIVITY.
WILL PASS THIS ON TO THE INCOMING SHIFT FOR FURTHER CONSIDERATION.
OTHERWISE, VERY HOT AND HUMID ONCE AGAIN TODAY WITH HIGHS IN THE LOW-
90S, DEW POINTS WELL INTO THE 70S RESULTING IN HEAT INDICIES OF 100-
105 (AS SEEN YESTERDAY).
ON THURSDAY, THE 500MB RIDGE FOLDS SOMEWHAT IN RESPONSE TO A
DISTURBANCE WRAPPING UP OVER INTERIOR ONTARIO. THE RESULT LOCALLY IS
AN INCREASING CHANCE FOR SHOWERS AND THUNDERSTORMS AS THE DAY
PROGRESSES. TIMING IS UNCERTAIN, WITH SOME GUIDANCE FAVORING THE
OVERNIGHT PERIOD INSTEAD OF THE LATE-AFTERNOON. OUR HOT AND HUMID
ENVIRONMENT WILL BE SUPPORTIVE OF ISOLATED SEVERE THUNDERSTORMS,
BUT THIS RISK IS HIGHLY CONDITIONAL ON HOW ANY UPSTREAM ACTIVITY
EVOLVES. THESE STORMS ALSO DECREASE FORECAST CONFIDENCE IN THE
TEMPERATURE FORECAST FOR THURSDAY. DUE TO ANTICIPATED CLOUD DEBRIS,
WE'LL HOLD OFF ON ANY EXTENSION OF THE HEAT ADVISORY.
WITH THE UPPER-LEVEL RIDGE SOMEWHAT DISPLACED, WE COULD REMAIN
WITHIN AN ACTIVE PERIOD INTO AT LEAST THE START OF THE LABOR DAY
WEEKEND WITH SHOWERS AND STORMS AROUND BOTH FRIDAY AND SATURDAY.
BEYOND THIS, THERE IS SOME INDICATION THE RIDGE MAY WASH BACK NORTH
EARLY NEXT WEEK. HIGH TEMPERATURES MONDAY AND TUESDAY HAVE A
COMICALLY LARGE SPREAD (10+ DEGREES TUESDAY) AMONG THE GUIDANCE,
WITH THE IN-HOUSE BLEND ON THE COOL-SIDE. WITH THAT MUCH SPREAD,
PRECIPITATION CHANCES ARE LIKEWISE UNCLEAR. GIVEN THE TROUGH WORKING
ITS WAY ACROSS THE CASCADES AND THROUGH MONTANA, I WOULD FAVOR THE
RIDGE AXIS TO REVISIT INDIANA EARLY IN THE WEEK. NO SIGNS OF FALL
QUITE YET.
AVIATION /12Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 611 AM EDT WED SEP 2 2026
EXISTING TAFS REMAIN ON TRACK AT THIS TIME. UPSTREAM CONVECTION
OVER IA AND WI WILL SEND CLOUD DEBRIS THROUGH KSBN AND, TO A
LESSER EXTENT, KFWA DURING THE MORNING HOURS. CONDITIONS LOOK
MAINLY DRY, BUT GIVEN THE HOT AND HUMID CONDITIONS AND PERHAPS
A LINGERING OUTFLOW BOUNDARY FROM IA, CANNOT COMPLETELY RULE OUT
AN ISOLATED THUNDERSTORM THIS AFTERNOON; CONFIDENCE IS LOW.
LATE IN THIS TAF PERIOD, AFTER 06Z, STORMS ARE EXPECTED TO
DEVELOP OVER SOUTHERN OR CENTRAL MICHIGAN AND DRIFT EAST-
SOUTHEAST. A DRY FORECAST CONTINUES, BUT THIS ACTIVITY MAY NEED
TO BE ADDRESSED JUST BEYOND THIS TAF PERIOD.
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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