854
FXUS63 KLOT 282340
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
640 PM CDT MON JUL 28 2025
KEY MESSAGES
- DANGEROUS HEAT AND HUMIDITY WITH A HEAT ADVISORY IN EFFECT
THROUGH EARLY THIS EVENING.
- PERIODS OF THUNDERSTORMS TUESDAY THROUGH THURSDAY MORNING,
SOME POSSIBLY STRONG/SEVERE WITH TORRENTIAL RAIN WHICH COULD
LEAD TO LOCALIZED FLASH FLOODING.
- DANGEROUS SWIMMING CONDITIONS AT LAKE MICHIGAN BEACHES
WEDNESDAY INTO THURSDAY, POSSIBLY THROUGH FRIDAY NIGHT.
DISCUSSION
ISSUED AT 230 PM CDT MON JUL 28 2025
THROUGH THIS EVENING:
WE REMAIN IN A HOT AND HUMID AIRMASS TODAY, WITH THESE CONDITIONS
FUELING ISOLATED CONVECTION ACROSS NORTHEAST ILLINOIS AND NORTHWEST
INDIANA CLOSER TO THE LAKE. FORCING FOR THIS CONVECTION HAS BEEN
TIED TO A WEAK LOCALIZED COLD FRONT/OUTFLOW FROM AN MCV THAT CROSSED
SOUTHERN WISCONSIN EARLY THIS MORNING. THIS BOUNDARY HAS BEEN
DRIFTING SOUTHWARD TODAY AND IS CURRENTLY LOCATED FROM NEAR ROCKFORD
TO NORTHWEST COOK COUNTY. MEANWHILE, AN OUTFLOW-ENHANCED LAKE BREEZE
HAS SURGED WESTWARD ACROSS THE CHICAGO METRO, WITH THE ORIGINAL LAKE
BREEZE DRIFTING SOUTHWARD OVER NORTHWEST INDIANA. EARLY AFTERNOON
AIRCRAFT OBS AND SATELLITE TRENDS INDICATE THAT MID-LEVEL DRYING AS
WELL AS SUBTLE MID-LEVEL WARMING ARE SUPPRESSING MOST OF THE
THUNDERSTORM ACTIVITY. THIS TREND SHOULD CONTINUE THROUGH THE
REMAINDER OF THE AFTERNOON, BUT WITH A GENERALLY UNCAPPED
ENVIRONMENT STILL IN PLACE SOUTH AND WEST OF THE BOUNDARIES,
ISOLATED CONVECTION REMAINS A POSSIBILITY INTO EARLY EVENING OVER
THE SOUTHWEST HALF OF THE CHICAGO METRO EASTWARD TO AROUND THE
KANKAKEE RIVER VALLEY IN NORTHWEST INDIANA. BEYOND THE DIURNALLY
DRIVEN ISOLATED STORMS THROUGH EARLY EVENING, DRY CONDITIONS ARE
EXPECTED INTO THE EARLY OVERNIGHT HOURS.
HAVE MAINTAINED THE HEAT ADVISORY FOR THE ENTIRE AREA THIS AFTERNOON
EVEN AS THE LAKE BREEZE AND ISOLATED STORMS HAVE PROVIDED SOME
RELIEF FROM THE HEAT CLOSER TO THE LAKE (PRIMARILY COOK AND LAKE
COUNTY IL). HEAT INDEX VALUES BEHIND THE BOUNDARIES AND STORMS ARE
STILL UP TO 100F AS OF 2PM. WITH REMAINING DAYTIME HEATING AND DEW
POINTS STILL IN THE MID 70S, HEAT INDEX VALUES COULD STILL REACH
105F AGAIN. ELSEWHERE OVER THE ADVISORY AREA, CURRENT HEAT INDEX
VALUES OF 100-105F ARE ON TRACK TO MEET ADVISORY CRITERIA OF 105F OR
HIGHER FOR MOST LOCATIONS.
KLUBER
EARLY TUESDAY THROUGH MONDAY:
PRIMARY FORECAST CONCERN IS THE POTENTIAL FOR AT LEAST A FEW
ROUNDS THUNDERSTORMS THROUGH THURSDAY MORNING.
THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS SOUTHERN MN/
NORTHERN IA THIS EVENING AND QUICKLY MOVE SOUTHEAST REACHING
NORTHWEST IL IN THE PREDAWN HOURS IN A DECAYING PHASE. HOW FAST
THESE DISSIPATE IS UNCERTAIN AND CURRENT GUIDANCE IS GENERALLY
IN AGREEMENT THAT THIS ACTIVITY WILL DISSIPATE ACROSS THE
NORTHERN CWA. GIVEN THE COVERAGE OF ACTIVITY THIS MORNING, WHICH
WAS HIGHER THAN ALL GUIDANCE WAS SHOWING 24 HOURS AGO, HAVE
INCREASED POPS TO HIGH CHANCE ACROSS THE NORTHERN CWA AROUND
DAYBREAK WITH POPS THEN STEADILY DIMINISHING THROUGH MID/LATE
MORNING. ADJUSTMENTS WILL BE NEEDED WITH LATER FORECASTS AS
TRENDS EMERGE. WITH THE EXPECTED WEAKENING TREND, AN ISOLATED
STRONG, POSSIBLY SEVERE STORM WOULD BE POSSIBLE ACROSS THE
NORTHWEST CWA.
AS HAPPENED TODAY, THE WIND FIELD WILL LIKELY BE DISTURBED WITH
ANY WEAKENING SHOWERS/STORMS, WHICH WILL LEAD TO A LAKE BREEZE
TUESDAY AFTERNOON AND SIMILAR TO TODAY AND ON SUNDAY, ISOLATED
THUNDERSTORMS WILL AGAIN BE POSSIBLE TUESDAY AFTERNOON NEAR THE
LAKE BREEZE. THERE IS ALSO THE POTENTIAL FOR A FEW THUNDERSTORMS
AWAY FROM THE LAKE BREEZE, ESPECIALLY ACROSS NORTHWEST IL. THERE
DOESN'T SEEM TO BE MUCH OF A FOCUS, BESIDES THE LAKE BREEZE BUT
WILL CONTINUE LOW CHANCE POPS FOR THE ENTIRE AREA.
GUIDANCE HAS LOWERED HIGH TEMPS BY SEVERAL DEGREES FOR TUESDAY
WITH HIGHS NOW GENERALLY IN THE UPPER 80S/AROUND 90. DEWPOINTS
WILL LIKELY BE SIMILAR TO TODAY, GENERALLY MID 70S. THIS WOULD
ALLOW FOR PEAK HEAT INDICES IN THE 95-100 RANGE. POSSIBLE FOR
SOME AREAS TO GET INTO THE 100-105 RANGE, ESPECIALLY ACROSS THE
SOUTHWEST CWA AND CURRENTLY NOT PLANNING ANY HEAT HEADLINES FOR
TUESDAY.
A COLD FRONT WILL MOVE SOUTH ACROSS THE AREA TUESDAY NIGHT INTO
WEDNESDAY. HOW MUCH THUNDERSTORM COVERAGE TUESDAY NIGHT THROUGH
WEDNESDAY NIGHT IS QUITE UNCERTAIN AS THIS FRONT MAY PUSH THE
BULK OF THE HEAVIER THUNDERSTORMS INTO AT LEAST THE SOUTHERN
CWA, POSSIBLY SOUTH OF THE CWA. CONFIDENCE IS VERY LOW AND
CURRENT BLENDED POPS ARE HIGH CHANCE TO LIKELY AND THIS SEEMS
REASONABLE FOR NOW. STRONG/SEVERE THUNDERSTORMS ARE POSSIBLE,
ESPECIALLY TUESDAY NIGHT INTO WEDNESDAY AS WELL AS HEAVY RAIN
AND LOCALIZED FLASH FLOODING.
THERE APPEARS TO BE A FEW PUSHES OF NORTHERN WINDS, ONE ON
WEDNESDAY AND ANOTHER ON THURSDAY THAT WILL EVENTUALLY PUSH ALL
OF THE PRECIP CHANCES SOUTH OF THE CWA BY THURSDAY AFTERNOON.
DEWPOINTS WILL DROP INTO THE 60S THURSDAY AND INTO THE 50S ON
FRIDAY BRINGING MUCH LESS HUMID CONDITIONS.
THE STRONGER NORTHERLY WINDS WILL ALLOW FOR HIGH WAVES AND
DANGEROUS SWIMMING CONDITIONS AT LAKE MICHIGAN BEACHES FROM
WEDNESDAY AFTERNOON THROUGH AT LEAST THURSDAY NIGHT AND POSSIBLY
INTO FRIDAY. CMS
AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 639 PM CDT MON JUL 28 2025
MOST OF TONIGHT SHOULD BE QUIET WITH NEARLY CALM WINDS AND
INITIALLY CLEAR SKIES POTENTIALLY ALLOWING FOR SOME SHALLOW
GROUND FOG TO DEVELOP AT DPA, GYY, AND PERHAPS RFD. OF GREATER
CONCERN WILL BE THE EVENTUAL EVOLUTION OF THE THUNDERSTORMS
DEVELOPING FROM WESTERN MN SOUTHWEST ACROSS SD AND INTO NORTHERN
NE. THESE STORMS ARE EXPECTED TO CONSOLIDATE INTO ONE OR TWO
FAST MOVING LINES OF SEVERE THUNDERSTORMS THIS EVENING AND BEGIN
RACING EAST-SOUTHEAST ACROSS IA AND SOUTHERN MN THROUGH THE
LATE EVENING. THE LINE(S) OF STORMS SHOULD BEGIN ENCOUNTERING AN
INCREASING UNFAVORABLE ENVIRONMENT FOR STORMS AS THEY NEAR THE
MISSISSIPPI RIVER WELL AFTER MIDNIGHT. THE BIG QUESTION IS HOW
QUICKLY THEY WILL DISSIPATE AND WHAT, IF ANYTHING, WILL BE LEFT
OF THESE STORMS AS THEY REACH OUR TERMINALS. THE THREAT OF
THUNDER SEEMS PRETTY LOW FOR THE IMMEDIATE CHICAGO TERMINALS, SO
JUST HAVE A PROB30 FOR -SHRA AND SQUIRRELLY WINDS THERE. FOR
RFD, MAINTAINED THE TSRA IN THE PROB30, SINCE THERE IS A BETTER,
ALBEIT STILL LOW, CHANCE OF THUNDER MAKING IT TO RFD.
FORECAST FOR WIND DIRECTION TOMORROW IS GOING TO HINGE PRETTY
HEAVILY ON WHAT THE DECAYING THUNDERSTORM CLUSTER DOES TO THE
WINDS. FOR IMMEDIATE CHICAGO AREA TERMINALS, THE LINGERING
EFFECTS OF THE DECAYED/DECAYING STORMS COULD RESULT IN A WIND
SHIFT TO NORTHWEST, THEN BACK TO EAST, THEN POTENTIALLY BACK TO
SOUTHWEST/WEST, BEFORE A POTENTIAL AFTERNOON LAKE BREEZE SENDS
WINDS BACK TO EASTERLY DIRECTION. OBVIOUSLY, THIS ALL SUGGESTS A
LOW CONFIDENCE FORECAST. OTHER THAN A PERIOD OF BRIEFLY STRONGER
AND GUSTY WINDS WITH INITIAL OUTFLOW FOR DYING STORMS, WINDS DO
LOOK TO MOSTLY REMAIN BELOW 10 KT TUESDAY.
- IZZI
LOT WATCHES/WARNINGS/ADVISORIES
IL...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
ILZ105-ILZ106-ILZ107-ILZ108.
IN...HEAT ADVISORY UNTIL 8 PM CDT /9 PM EDT/ THIS EVENING FOR
INZ001-INZ002-INZ010-INZ011-INZ019.
LM...NONE.
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