156
FXUS63 KIWX 040935
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
535 AM EDT FRI SEP 4 2026
KEY MESSAGES
- HEAT AND HUMIDITY CONTINUE WITH PEAK HEAT INDICES AROUND 100
DEGREES.
- 20-40% CHANCE OF THUNDERSTORMS TODAY AND TONIGHT. WIDESPREAD
SEVERE WEATHER IS NOT EXPECTED, BUT DAMAGING WIND GUSTS AND
HAIL CANNOT BE RULED OUT.
- A DRY PATTERN TAKES OVER SUNDAY THROUGH TUESDAY.
DISCUSSION
ISSUED AT 238 AM EDT FRI SEP 4 2026
ANOTHER MURKY FORECAST PERIOD LIES AHEAD WITH RESPECT TO
THUNDERSTORMS TODAY. FIRST, THE HEAT ADVISORY WAS EXPANDED ONCE
AGAIN TO ENCOMPASS REMAINING NORTHERN INDIANA COUNTIES AND A
MAJORITY OF NORTHWEST OHIO COUNTIES (EXEMPT ARE WILLIAMS AND
FULTON). MICHIGAN IS ALSO EXEMPT. HEAT INDICIES ONCE AGAIN APPROACH
100F THIS AFTERNOON. OBSERVATIONS ON THURSDAY SHOWED SOME SITES
REACHING HEAT ADVISORY CRITERIA BY NOON, IF NOT THE 11AM HOUR. HIGH
CLOUDS THIS MORNING COULD BRIEFLY TEMPER HEAT INDICIES, BUT
AFTERNOON SUN COULD EASILY FLIP THE SCRIPT. WHILE DURATION OF
ADVISORY CRITERIA MAY BE LIMITED TODAY IN SOME AREAS, WE CAN THEN
PLAY THE CONSECUTIVE-DAYS CARD AS WE STARE DOWN THE PROSPECT OF OUR
4TH CONSECUTIVE VERY HOT DAY.
ONGOING THIS MORNING IS AN INCREASINGLY MATURE AREA OF THUNDERSTORMS
OVER CENTRAL WI. FORECAST GUIDANCE GENERALLY SUGGESTS THIS CLUSTER
WILL WEAKEN AS IT CROSSES INTO WESTERN MICHIGAN AFTER SUNRISE.
HOWEVER, THE INSTABILITY GRADIENT COULD LEAD ANY LINGERING STORMS
INTO SOUTHERN MICHIGAN WHILE EFFECT SHEAR OF 40 KNOTS COULD AID IN
THUNDERSTORM MAINTENANCE. THIS IS AT ODDS WITH LACKING LAPSE RATES
LESS THAN 7 C/KM. CONFIDENCE IS LOW ON HOW THESE STORMS EVOLVE FOR
THE REMAINDER OF THE MORNING, BUT THEY WILL BE MONITORED CLOSELY
PRIOR TO SUNRISE.
LIKE 24 HOURS AGO, OUR MARGINAL RISK OF SEVERE THUNDERSTORMS WAS
UPGRADED TO A SLIGHT RISK THIS MORNING. THIS IS PRIMARILY DRIVEN BY
THE ANTICIPATED DEVELOPMENT OF THUNDERSTORMS THIS EVENING AMID A
STRENGTHENING 500-MB JET IN WHICH WE LIE WITHIN THE RIGHT-ENTRACNE
REGION. THE LOW-LEVEL JET STRENGTHENS AS WELL. TIMING IS NEARLY A
TOSS UP IN THIS CHALLENGING, NUANCED MESOSCALE ENVIRONMENT, YET
SOMETIME AFTER 8PM EDT APPEARS PROBABLE FOR STORMS TO REDEVELOP.
CONFIDENCE IS LOW, BUT DAMAGING WIND GUSTS AND HAIL WOULD BE THE
PRIMARY HAZARDS FROM ANY SEVERE STORMS TODAY AND TONIGHT.
DRYING OUT SATURDAY IN THE WAKE OF ANY EARLY-MORNING LINGERING
THUNDERSTORMS AND NOT QUITE AS HOT AS THE UPPER-LEVEL JET BUCKLES.
BY SUNDAY, CANADIAN HIGH PRESSURE SEEPS IN FROM THE NORTHEAST,
SHUNTING THE UPPER-LEVEL RIDGE OUT OF OUR AREA FOR A TIME AND
BRINGING US A PERIOD OF DRY WEATHER AS WELL. LOOK FOR SURFACE LOW
PRESSURE TO CROSS THE CANADIAN PRAIRIE MIDWEEK, WITH A COLD FRONT
TRACKING ACROSS THE NORTHERN AND CENTRAL PLAINS. THIS COLD FRONT
LOOKS TO BRING RATHER UNIFORM COVERAGE OF SHOWERS AND THUNDERSTORMS
TO OUR AREA AROUND MIDWEEK. BEYOND WEDNESDAY, THERE IS VARYING
MAGNITUDES OF OUR WELL-DISCUSSED UPPER-LEVEL RIDGE, NOW DISPLACED
THROUGH THE MID-MISSISSIPPI VALLEY. THIS RIDGE MAY BUILD BACK NORTH
BRINGING CONTINUED WARMTH, OR, THE COLD FRONT COULD HANG-UP ATOP
THIS RIDGE KEEPING US IN LINE FOR ADDITIONAL LATE-WEEK STORMS.
AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 535 AM EDT FRI SEP 4 2026
AS HYPOTHESIZED IN THE PREVIOUS DISCUSSION, THE AFORMENTIONED
THUNDERSTORMS ACROSS WI HAVE MAINTAINED THEMSELVES, FEEDING OFF
FAVORABLE SHEAR AND AN INSTABILITY GRADIENT STEERING THE
COMPLEX ESE. ISOALTED CELLS PERCOLATE ACROSS SOUTHERN WI,
CENTRAL LAKE MICHIGAN AND NOW SOUTHERN MI. THUS, THERE APPEARS
TO BE ENOUGH EVIDENCE TO MAINTAIN A PROB30 AT KSBN. THE CURRENT
TRAJECTORY COULD STILL STEER THE COMPLEX JUST NORTH OF THE
AIRPORT; PROMPTING THE CONTINUED PRBO30. KFWA STILL LOOKS TO
STEER-CLEAR OF THIS ACTIVITY; MEDIUM CONFIDENCE.
THE OVERNIGHT HOURS ARE UNCERTAIN WITH RESPECT TO
THUNDERSTORMS. UNRELIABLE HIGH-RESOLUTION GUIDANCE SUGGESTS
TSRA AT BOTH SITES IN THE 06-09Z WINDOW.WILL PASS THIS ON TO THE
NEXT SHIFT AS MODELS ARE HARDLY HANDLING THIS ONGOING
CONVECTION VERY WELL.
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 OHZ004-005-015-
016-024-025.
MI...NONE.
MARINE...NONE.
DISCUSSION...BROWN
AVIATION...BROWN
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