518
FXUS63 KIWX 250126
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
926 PM EDT THU JUL 24 2025
KEY MESSAGES
- THUNDERSTORMS ARE EXPECTED TO INCREASE IN COVERAGE OVERNIGHT
THROUGH FRIDAY MORNING, WITH VERY HEAVY RAINFALL THE PRIMARY
THREAT. GUSTY WIND IS POSSIBLE AS WELL.
- DANGEROUS HEAT RETURNS FOR MONDAY AND TUESDAY.
UPDATE
ISSUED AT 925 PM EDT THU JUL 24 2025
SHOWERS AND THUNDERSTORMS CONTINUE TO DIMINISH IN COVERAGE AS
OF THIS WRITING. STORMS HAD DEVELOPED ALONG A COLD FRONT OVER
NORTHWEST ILLINOIS. STORMS RACED EAST WITHIN THEIR OWN FAVORABLE
MESOSCALE ENVIRONMENT, EFFECTIVELY LEAVING THE FRONT BEHIND. AS
A RESULT, SURFACE OBSERVATIONS DEPICT COOLER TEMPERATURES, BUT
DEW POINTS REMAIN HIGH (WELL INTO THE 70S) AND CONDUCIVE FOR
MORE STORMS.
A LINE OF STORMS IS ONGOING OVER NORTHERN MO, TRACKING EAST.
MEANWHILE, WATER VAPOR DEPICTS AN MCV OVER EAST-CENTRAL IL. HIGH
RESOLUTION GUIDANCE CONTINUES TO SUGGEST THAT STORMS WILL DEVELOP
ALONG THE LINGERING COLD FRONT FROM NORTHERN MO TO FAR NORTHWEST IN
OVERNIGHT. FORECAST MUCAPE OF 1,000 J/KG WILL BE CONDUCIVE FOR
THUNDERSTORMS WHILE THE FRONT AND AFORMENTIONED MCV SERVE AS THE
FORCING MECHANISMS (LINGERING OUTFLOW FROM THIS EVENINGS STORMS IS
AN ADDITIONAL FORCING MECHANISM).FORECAST SOUNDINGS DEPICT THIS
ELEVATED INSTABILITY, BUT A SHARP CAPPING INVERSION WILL NEED TO BE
OVERCOME. RAIN RATES IN EXCESS OF 1" PER HOUR AND DAMAGING WIND
GUSTS WILL CONTINUE TO BE THE PRIMARY HAZARDS.
DISCUSSION
ISSUED AT 102 PM EDT THU JUL 24 2025
A VERY HOT & HUMID AFTERNOON ACROSS THE REGION TODAY W/ CURRENT
ACTUAL AIR TEMPERATURES (AS OF 1 PM EDT) IN THE 90S AND SURFACE
DEW POINTS IN THE MIDDLE TO UPPER 70S CONTRIBUTING TO HEAT INDEX
VALUES RANGING FROM 100-105 DEG F. A HEAT ADVISORY REMAINS IN
EFFECT UNTIL 8 PM EDT THIS EVENING. CONVECTIVE CHANCES ARE STILL
EXPECTED TO INCREASE LATER THIS AFTERNOON THROUGH TONIGHT,
THOUGH CONSIDERABLE UNCERTAINTY STILL EXISTS WITH REGARD TO
TIMING AND COVERAGE GIVEN THE WEAKLY FORCED ENVIRONMENT BENEATH
THE UPPER RIDGE WITH A LACK OF LIFTING MECHANISMS OTHER THAN
REMNANT OUTFLOW AND VERY WEAK SURFACE CONVERGENCE OVER
PRIMARILY NORTHWESTERN AREAS. CAMS CONTINUE TO STRUGGLE WITH A
FAVORED MOST LIKELY TIME FRAME FOR STORMS, RANGING ANYWHERE FROM
21Z TO 02Z WITH SOME HIGH-RES MODELS NOT EVEN SHOWING MUCH AT
ALL UNTIL AFTER 06-09Z. SOME CONCERNS THAT THE RELATIVELY DRY
BIAS ON RECENT HRRR RUNS MAY BE THE RESULT OF OVER-MIXING, BUT
THERE IS STILL VERY LITTLE HREF SUPPORT FOR MORE WIDESPREAD
STORMS DURING THE EVENING. IF STORMS DEVELOP, THE HIGH PWATS
COUPLED WITH WEAK SHEAR AND DCAPE AROUND 900-1000 J/KG SUGGESTS
POTENTIAL FOR LOCALLY DAMAGING WIND GUSTS WITH ANY STRONGER
CORES, BUT NOT OVERLY CONVINCED THAT ANYTHING WILL BE AS
ORGANIZED AS THE SQUALL LINE SUGGESTED BY THE NAMNEST.
NATURALLY, GIVEN THE EXTREMELY MOIST PROFILES IT IS LIKELY THAT
ANY STORMS WILL BE VERY EFFICIENT RAINFALL PRODUCERS WITH THE
POTENTIAL FOR LOCALIZED FLOODING, ESPECIALLY GIVEN THE FLOW NOT
BEING PARTICULARLY STRONG.
HIGHER CONFIDENCE EXISTS IN SHOWERS AND STORMS BECOMING MORE
WIDESPREAD OVERNIGHT THROUGH FRIDAY AS NUMEROUS DISTURBANCES
TRAVERSE THE FLOW ALONG THE SLOW-MOVING SYNOPTIC BOUNDARY,
LIKELY RESULTING IN MULTIPLE ROUNDS/CLUSTERS OF STORMS THROUGH
THE FRIDAY MORNING. WEAK INSTABILITY SHOULD PRECLUDE ANY KIND OF
SUBSTANTIAL SEVERE RISK, BUT PWAT VALUES OF 2-2.25 INCHES ALONG
WITH VERY DEEP/WARM/SATURATED THERMODYNAMIC PROFILES WOULD
SUGGEST POTENTIAL FOR EXTREMELY HEAVY RAINFALL WITH SOME SHOWERS
AND STORMS. LATEST EROS FOR DAY 1 AND 2 INDICATE A SLIGHT RISK
FOR EXCESSIVE RAINFALL FOR TONIGHT THROUGH TOMORROW. THIS FIRST
ROUND OF HEAVY RAIN MAY END BY EARLY AFTERNOON, AND IT REMAINS
UNCLEAR HOW ANY MORNING CONVECTION WILL IMPACT SURFACE HEATING
AND ANY ADDITIONAL STORMS IN THE EVENING. CONVECTIVE CHANCES MAY
RETURN FOR SATURDAY AS WELL, BUT ONCE AGAIN CONFIDENCE REMAINS
LOW GIVEN THE STAGNANT PATTERN WITH ONLY MODEST FORCING
MECHANISMS.
WIDESPREAD SHOWERS AND STORMS SHOULD PRECLUDE THE NEED FOR ANY
HEAT RELATED HEADLINES THIS WEEKEND, BUT MODELS REMAIN IN VERY
GOOD AGREEMENT W/ A SWATH OF UPPER 70S TO NEAR 80 DEG F DEW
POINTS DEVELOPING BY MONDAY AND TUESDAY OF NEXT WEEK, WHICH
COMBINED WITH TEMPERATURES IN THE LOWER TO MIDDLE 90S WILL HELP
HEAT INDICES SOAR TO 100-105 F TO PERHAPS 105+ F ACROSS A MUCH
LARGER AREA THAN TODAY. AT A MINIMUM, FULLY EXPECT ANOTHER HEAT
ADVISORY WILL BE NEEDED FOR EARLY NEXT WEEK.
AVIATION /00Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 714 PM EDT THU JUL 24 2025
OUTFLOW BOUNDARY IS CRUISING SOUTHEAST TOWARD KFWA. A WIND SHIFT
TO THE NORTHWEST IS EXPECTED WITH A WIND GUST OF 25KTS, PERHAPS
AS GREAT AS 35 KTS.
SHOWERS TAPER OFF AT KSBN FOR A TIME THIS EVENING, BUT PLENTY OF
SHOWERS AND STORMS ARE NOTED UPSTREAM ACROSS ILLINOIS. TONIGHT'S
EVOLUTION OF SHOWERS AND STORMS OFFERS LOW CONFIDENCE, BUT
GUIDANCE CONTINUES TO KEY IN ON A CLUSTER OF STORMS ALONG AN
AREA FROM CHAMPAIGN, TO LAFAYETTE, TO FORT WAYNE FROM ABOUT
09Z-12Z OR SO. THIS WILL NEED TO BE MONITORED FOR THE 06Z TAF
CYCLE.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...NONE.
UPDATE...BROWN
DISCUSSION...HAMMER
AVIATION...BROWN
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