418
FXUS63 KIWX 231940
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
340 PM EDT WED JUL 23 2025
KEY MESSAGES
- VERY HOT AND HUMID AIRMASS OVERSPREADS THE AREA
TONIGHT/THURSDAY. HIGHS IN THE LOWER 90S WILL LEAD TO PEAK
AFTERNOON HEAT INDICES OF 100 TO 105 (HIGH CONFIDENCE)
THURSDAY WITH A POTENTIAL OF SOME AREAS REACHING 105 TO 110
(LOWER CONFIDENCE).
- CHANCES FOR SHOWERS AND THUNDERSTORMS BEGIN TO INCREASE LATE THURSDAY
AFTERNOON INTO EVENING ALONG AND NORTH OF US-6, SPREADING
SOUTH OVERNIGHT. AN ISOLATED DAMAGING WIND THREAT AND LOCALLY
HEAVY RAINFALL WOULD BE THE POTENTIAL MAIN THREATS.
- SHOWER STORM CHANCES CONTINUE FRIDAY AND SATURDAY WITH A GOOD
DEAL OF UNCERTAINTY REMAINING REGARDING COVERAGE/TIMING. EARLY
INDICATIONS SUGGEST BEST CHANCES EARLY FRIDAY, AND THEN AGAIN
LATE FRIDAY NIGHT INTO SATURDAY. LOW CONFIDENCE IN ADDITIONAL
STORM CHANCES LATE WEEKEND/EARLY NEXT WEEK.
- HEAT ADVISORY CRITERIA MAY BE REACHED AGAIN IN THE SUNDAY AND MONDAY
TIMEFRAME, BUT WILL DEPEND ON CLOUD COVER AND ANY SHOWERS OR
STORMS.
DISCUSSION
ISSUED AT 337 PM EDT WED JUL 23 2025
NO CHANGES WILL BE MADE TO HEAT HEADLINES AT THIS TIME, WITH ONGOING
HEAT ADVISORY WEST OF US ROUTE 31, AND THE REMAINDER OF THE FORECAST
ARE JOINING THE ADVISORY FOR THURSDAY.
A VERY STRONG LOW LEVEL THETA-E GRADIENT PERSISTS THIS EVENING. THE
LEADING EDGE OF THIS GRADIENT IS QUITE EVIDENT ON SURFACE OBS AND
SATELLITE IMAGERY, WITH ENHANCED CU FIELD ROUGHLY JUST WEST OF A
SOUTH BEND TO ROCHESTER TO KOKOMO LINE MARKING THE LEADING EDGE OF
MORE SIGNIFICANT LOW LEVEL MOISTURE. A STRONG INSTABILITY GRADIENT
ACCOMPANIES THIS MOISTURE AXIS WITH PRIMARY INSTABILITY AXIS AT 19Z
EXTENDING FROM EAST CENTRAL IL TO THE CHICAGO AREA. MAIN AREA OF LOW
LEVEL CONFLUENCE SHOULD REMAIN ANCHORED ACROSS EXTREME NW IN AND
INTO NE ILLINOIS THIS EVENING WHERE A FEW SHOWERS/STORMS COULD
DEVELOP THROUGH EARLY EVENING AT LEADING EDGE OF THIS INSTABILITY
GRADIENT. AN EARLIER IN THE DAY MCV WAS AIDING IN DEVELOPMENT OF
ISOLATED CONVECTION ACROSS NORTHERN ILLINOIS, BUT THIS FEATURE HAS
DEPARTED TO THE NORTHEAST. WILL KEEP SOME SILENT 10 POPS INTO EARLY
EVENING ACROSS THE EXTREME WESTERN PORTIONS OF THE FORECAST AREA
WITH EXPECTATION BEST ISOLATED POTENTIAL WILL REMAIN ACROSS
NE/CENTRAL ILLINOIS.
A COMPLEX MID/UPPER LEVEL FLOW PATTERN ACROSS CENTRAL CONUS WILL
ALLOW A SERIES OF WAVES TO EJECT EASTWARD ACROSS THE GREAT LAKES
REGION INTO THURSDAY ASSOCIATED WITH BOTH NORTHERN STREAM, AND
ADDITIONAL CUT-OFF SHORT WAVES IN SOUTHERN STREAM. APPROACH OF THESE
SHORT WAVES AND CONTINUED DEPARTURE OF MID ATLANTIC ANTICYCLONE
WILL ALLOW FOR SLIGHT VEERING/STRENGTHENING OF LOW LEVEL
SOUTHWEST FLOW ON THURSDAY. THIS WILL BE A FAVORABLE TRAJECTORY
TO ADVECT THE MUCH HIGHER THETA-E AIR UPSTREAM INTO THE LOCAL
AREA FOR THURSDAY. DEW POINTS IN THE MID 70S TO AS HIGH AS 80 IN
A FEW SPOTS STILL APPEAR LIKELY WITH LOW LEVEL THERMAL PROGS
SUPPORTING HIGHS INTO LOWER 90S ACROSS MUCH OF THE AREA. AS
PREVIOUS FORECAST MENTIONED, SOME HIGH CLOUD DEBRIS COULD SPREAD
ACROSS THE AREA FROM UPSTREAM CONVECTION WHICH WOULD HAVE
IMPACT ON TEMPS/HEAT INDICES. CONFIDENCE REMAINS HIGH IN
ADVISORY LEVEL HEAT INDICES. SOME ISOLATED WARNING AMOUNTS STILL
APPEAR TO BE A GOOD POSSIBILITY, ESPECIALLY ACROSS SOUTH
CENTRAL LOCATIONS WHICH WILL BE IN CORE OF LOW LEVEL MOIST
TONGUE AND FOR AREAS THAT MIGHT BE MORE IMMUNE FROM ANY HIGH
CLOUD DEBRIS. CONFIDENCE IS NOT HIGH ENOUGH AT THIS TIME TO GO
WITH A WARNING, AND WILL CONTINUE WITH HEAT ADVISORY HEADLINES
AND A MENTION OF ISOLATED HIGHER HEAT INDICES.
THE SERIES OF AFOREMENTIONED WAVES SHOULD DAMPEN RIDGE ENOUGH TO
ALLOW FOR INCREASED SHOWER/STORM CHANCES ALONG SOUTHWARD SAGGING
CONVERGENCE ZONE EARLY THURSDAY EVENING. HOWEVER, GOOD DEAL OF
UNCERTAINTY REMAINS IN TERMS OF STORM CHANCES LATE THU
AFTERNOON/EVENING DUE TO QUESTIONS WITH FORCING MECHANISMS. THE
HIGHLY SHEARED NATURE OF THE WAVES WILL RESULT IN LIMITED SOUTHWARD
PUSH TO FRONTAL ZONE WITH CONVERGENCE NOT EXPECTED TO BE
PARTICULARLY DEEP IN NATURE. WILL MAINTAIN LIKELY POPS BY THURSDAY
EVENING GIVEN MODERATE TO STRONG INSTABILITY PROFILES AND AT LEAST
AXIS OF SHALLOW LOW LEVEL CONVERGENCE SINKING SOUTH. SHEAR
PROFILES WILL BE LIMITED SO WOULD EXPECT OUTFLOW DOMINANCE TO
OCCUR FAIRLY QUICKLY WHICH COULD LIMIT ANY ISOLD SEVERE WIND
THREAT TO JUST A FEW HOURS AFTER INITIATION. SOME BETTER
COVERAGE SHOWERS/EMBEDDED STORMS COULD EVOLVE AGAIN LATER
THURSDAY NIGHT INTO FRIDAY AM IF UPSTREAM CONVECTIVELY ENHANCED
VORT MAX IS ABLE TO MATERIALIZE.
FRIDAY MAY FEATURE A LULL IN THE STRONGER MID/UPPER FORCING BUT WITH
WASHING OUT LOW LEVEL FRONT IN THE AREA, SCATTERED CONVECTION STILL
APPEARS A GOOD POSSIBILITY. HEAT SHOULD BE TEMPERED SOMEWHAT BY
GREATER CLOUD COVER/PRECIP ON FRIDAY WITH HEAT INDICES
REMAINING BELOW ADVISORY CRITERIA.
LATE FRIDAY NIGHT INTO SATURDAY COULD BE THE PERIOD TO WATCH FOR A
HIGHER POTENTIAL OF GREATER COVERAGE SHOWERS/STORMS AND HEAVY RAIN
POTENTIAL. BY SATURDAY, A DISTURBANCE CURRENTLY LIFTING NORTH ACROSS
S NEVADA IS EXPECTED TO TOP THE RIDGE WITH PERHAPS THE STRONGEST
LOW/MID LEVEL WESTERLY WIND PROFILES ACROSS THE SOUTHERN GREAT
LAKES OF THIS FORECAST PERIOD. A RENEWED LOW LEVEL THETA-E
ADVECTIVE SURGE MAY PRECEDE THIS SHORT WAVE. GUIDANCE DOES
SUGGEST WEAKENING PROPAGATION VECTORS IN THIS STRENGTHENING
WEST-SOUTHWEST FLOW REGIME. WARM CLOUD DEPTHS IN EXCESS OF 12K
FEET AND POCKET OF 2+ INCH PWATS COUPLED WITH THESE WEAK
PROPAGATION VECTORS COULD ALLOW FOR SOME HEAVY RAINFALL ACROSS
THE AREA ON SATURDAY. SOME ISOLATED SEVERE POTENTIAL MAY ALSO
EXIST, PARTICULARLY DOWNSTREAM OF ANY CONVECTIVELY ENHANCED VORT
WHERE SOME DESTABILIZATION CAN TAKE PLACE. OVERALL CONFIDENCE
IN SATURDAY SCENARIO REMAINS LOW HOWEVER, AS MUCH OF THIS THREAT
DEPENDS ON HOW THE UPSTREAM WAVE IS CONVECTIVELY MODIFIED WHICH
IS DIFFICULT TO DISCERN AT THIS FORECAST DISTANCE.
SOME INDICATIONS THAT MID/UPPER RIDGING TRIES TO REBUILD IN WAKE OF
SATURDAY WAVE FOR SUNDAY LEADING TO LOWER CONFIDENCE IN ISOLATED
CONVECTION SUN/MON. BUT ALSO INCREASED POSSIBILITY OF SOME AREAS
HAVING MORE HEAT ISSUES TO DEAL WITH. MEDIUM RANGE GUIDANCE DOES
SUGGEST SOME ADDITIONAL CHANCES OF SHOWERS AND STORMS WOULD BE
POSSIBLE TOWARD END OF PERIOD WITH NW FLOW WAVES POSSIBLE.
CONFIDENCE IS ALSO INCREASING BASED ON MEDIUM RANGE GUIDANCE
CONSENSUS IN LESS HUMID CONDITIONS DEVELOPING BY THE MIDDLE OF
NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 117 PM EDT WED JUL 23 2025
VFR CONDITIONS THROUGH AT LEAST THE NEXT 24 HOURS WITH SOUTH TO
SOUTHWESTERLY WINDS. A STRONG RIDGE OF HIGH PRESSURE WILL KEEP
SKIES MOSTLY CLEAR, ALTHOUGH CIRRUS MAY START TO INCREASE ON
THURSDAY MORNING AHEAD OF AN APPROACHING SHORTWAVE. SOUTHWEST
WINDS WILL ALSO INCREASE ON THURSDAY AND COULD BECOME GUSTY IN
THE AFTERNOON. THE NEXT CHANCE FOR SHOWERS AND THUNDERSTORMS IS
AFTER 18Z THURSDAY.
IWX WATCHES/WARNINGS/ADVISORIES
IN...HEAT ADVISORY FROM 11 AM TO 8 PM EDT THURSDAY FOR INZ005>009-
017-018-023>027-032>034-116-216.
HEAT ADVISORY UNTIL 8 PM EDT /7 PM CDT/ THURSDAY FOR
INZ012>015-020-022-103-104-203-204.
OH...HEAT ADVISORY FROM 11 AM TO 8 PM EDT THURSDAY FOR OHZ001-002-
004-005-015-016-024-025.
MI...HEAT ADVISORY FROM 11 AM TO 8 PM EDT THURSDAY FOR MIZ079>081.
HEAT ADVISORY UNTIL 8 PM EDT THURSDAY FOR MIZ078-177-277.
MARINE...NONE.
DISCUSSION...MARSILI
AVIATION...COBB
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