487
FXUS63 KIWX 091018
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
618 AM EDT SUN AUG 9 2026
KEY MESSAGES
- SEVERE THUNDERSTORMS THIS AFTERNOON AND TONIGHT PRESENT THE
RISK OF FLASH FLOODING AND DAMAGING WIND GUSTS. TORNADOES
CANNOT BE RULED OUT.
- ADDITIONAL SEVERE THUNDERSTORMS ARE POSSIBLE MONDAY AFTERNOON
AND EVENING.
- SEASONABLE TEMPERATURES ARE EXPECTED TO PERSIST.
DISCUSSION
ISSUED AT 301 AM EDT SUN AUG 9 2026
PLENTY OF UNCERTAINTY IN THE FORECAST TODAY, YET, DEPENDING ON WHICH
SOLUTION VERIFIES, HEAVY RAINFALL MAY PROVE THE MOST LIKELY HAZARD
THIS EVENING ALONG THE INDIANA-MICHIGAN STATE LINE. THIS IS IN
ADDITION TO THE DAMAGING WIND GUST AND TORNADO RISK FROM SEVERE
THUNDERSTORMS THIS AFTERNOON (LOW CONFIDENCE) AND OVERNIGHT (MEDIUM
CONFIDENCE).
AS IT GOES HERE IN NORTHERN INDIANA, ROUNDS OF STORMS ARE HIGHLY
DEPENDENT ON HOW ANY CONVECTION EARLIER IN THE DAY EVOLVES. EARLY
THIS MORNING, THE AREA TO WATCH IS OVER THE ND-SD STATE LINE WHERE A
GROWING COMPLEX OF STORMS EXISTS. THIS COMPLEX DRIFTS EAST AND INTO
NORTHEAST IL AND INTO IN THIS AFTERNOON. PREEXISTING HIGH PRESSURE
MAY BE THE ELEMENT GUIDANCE IS STRUGGLING WITH, ESPECIALLY IN
CONTRAST TO THE INCOMING WARM FRONT WHICH IS TIMED WELL TO SUPPORT
AFTERNOON CONVECTION. MID-LEVEL LAPSE RATES OF ABOUT 6.8 C/KM COULD
BE BETTER. ALOFT, A 45-KNOT JET COULD BE ENOUGH TO SUSTAIN STORMS,
YET THE BEST UPPER-LEVEL SUPPORT IS WELL NORTH ACROSS THE UPPER
GREAT LAKES. ENSEMBLE HIGH RESOLUTION GUIDANCE GENERALLY SUGGESTS A
WEAKENING LINE OF CONVECTION ARRIVES BY MID-AFTERNOON AND PRESENTS A
NON-ZERO CHANCE FOR DAMAGING WIND GUSTS AMID 1500 J/KG OF CAPE AND
ABOUT 30 KNOTS OF SHEAR.
GIVEN THE ANTICIPATED MODEST STATE OF THIS AFTERNOON'S CONVECTION,
ROUND TWO OVERNIGHT COULD PROVE MORE POTENT. STARTING WITH
THE HEAVY RAIN CONCERN, MULTIPLE FORECAST MODELS ARE LATCHING ONTO A
COMPLEX OF RAIN AND STORMS THAT BECOMES ANCHORED OVER SOUTH-
CENTRAL LAKE MICHIGAN EXTENDING EAST THROUGH THE INDIANA-MICHIGAN
STATE LINE. STORMS DEVELOP ALONG THE WARM FRONT AMID A STRENGTHENING
LOW-LEVEL JET. MICHIANA COMMUNITIES FROM LA PORTE AND MICHIGAN CITY,
EAST TO THE GREATER ELKHART-GOSHEN METRO AREAS COULD BE AT RISK FOR
URBAN FLOODING FROM RAIN RATES OF AT LEAST 1" PER HOUR
(LIKELY MORE) AND RAINFALL TOTALS IN EXCESS OF 2-2.5
INCHES IF FORECASTS VERIFY. BOUNDARY-PARALLEL FLOW (WHICH IS
ESPECIALLY WEAK AND CONVERGENT AT THE SURFACE), 500-MB DEW POINT
DEPRESSIONS OF 1 TO 2 C INDICATE A VERY DEEP MOISTURE PROFILE,
ALONG WITH WARM CLOUD DEPTHS NEARING 14,000 FT. SWIFT 850-MB FLOW OF
ABOUT 30-40 KNOTS AND GENERALLY DRY RECENT CONDITIONS MAY WORK TO
REDUCE THE FLOOD RISK. NONETHELESS, IF TRAINING STORMS CAN
DEVELOP, HEAVY RAIN AND LOCALIZED URBAN FLOODING ARE A CONCERN
TONIGHT.
IN ADDITION TO THE FLOODING THREAT, ANY SUPERCELLS THAT DEVELOP IN
THE VICINITY OF THE WARM FRONT POSE A RISK FOR ALL HAZARDS INCLUDING
TORNADOES. LAPSE RATES ONCE AGAIN POSE A CHALLENGE, AS DOES OVERALL
STORM EVOLUTION, BUT 0-1KM SRH OF NEARLY 300 M2/S2 RESULTS IN
SHALLOW BUT LOOPING HODOGRAPHS. THE PREVIOUSLY MENTIONED
MOISTURE-RICH ATMOSPHERE MAY PROVE CHALLENGING FOR HAIL, BUT AS
STORMS CONGEAL INTO A LINE, DAMAGING WIND GUSTS WOULD BECOME THE
PRIMARY HAZARD THROUGH EARLY MONDAY MORNING.
WE'LL FACE ANOTHER POSSIBLE ROUND OF SEVERE THUNDERSTORMS LATE
MONDAY AFTERNOON AND EVENING AS ENERGETIC UPPER-LEVEL FLOW REMAINS IN
PLACE. THIS TOO COULD POSE A HEAVY RAIN RISK WITH MANY OF THE SAME
INGREDIENTS IN PLACE. TUESDAY WILL BE WORTH WATCHING FOR MORE
STORMS UNTIL HIGH PRESSURE FINALLY NOES IN BY WEDNESDAY TO STEER
THIS ACTIVE PATTERN ELSEWHERE. LATE-WEEK LOW PRESSURE BRINGS ANOTHER
CHANCE FOR STORMS. HIGH TEMPERATURES WILL BE NEAR TO SLIGHTLY BELOW
NORMAL THROUGH THE 7-DAY PERIOD.
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 614 AM EDT SUN AUG 9 2026
PATCHY FOG HAS HAD LIMITED STAYING POWER AT MOST SITES EARLY
THIS MORNING AND HAS FAILED TO MATERIALIZE AS OF THIS WRITING
AT KSBN AND KFWA. AS A RESULT, WILL BACK-OFF THE PREVIOUSLY
MENTION BR. HIGH AND MID-LEVEL CLOUDS WILL SPREAD IN FROM THE
WEST THIS MORNING, ASSOCIATED WITH THUNDERSTORMS ONGOING ACROSS
IOWA. THESE STORMS ARE FORECAST TO WEAKEN AS THEY ARRIVE TO KSBN
AND BECOME MORE SCATTERED IN NATURE. WITH THIS GROWING
CONCENSUS, THE PROB30 HAS BEEN "UPGRADED". AT KFWA, CONDITIONS
STILL LOOK DRY DURING THE DAYLIGHT HOURS.
WE'LL MONITOR FOR ADDITIONAL TSRA EARLY MONDAY MORNING.
QUESTIONS REMAIN, PRIMARILY RELATED TO WHAT HAPPENS WITH THIS
FIRST CLUSTER OF STORMS OF IOWA. HOWEVER, TIMING IS COMING INTO
FOCUS AND IT APPEARS STORMS COULD BE MOST NUMEROUS AT KSBN.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...NONE.
DISCUSSION...BROWN
AVIATION...BROWN
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