724
FXUS63 KLOT 301730
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1230 PM CDT TUE JUN 30 2026
KEY MESSAGES
- DANGEROUS HEAT WAVE WILL LIKELY CONTINUE INTO THURSDAY FOR
MOST IF NOT ALL OF THE AREA WITH DAYTIMES HIGHS IN THE 90S AND
PEAK AFTERNOON HEAT INDICES OF 100 TO 110 DEGREES. CONFIDENCE
ACROSS FAR NORTHERN IL IS LOWER THURSDAY, DUE TO POTENTIAL
EFFECT OF STORMS.
- THUNDERSTORM CHANCES WILL BEGIN TO INCREASE LATE IN THE WEEK,
LIKELY BRINGING SOME HEAT RELIEF FOR AT LEAST SOME AREAS.
- WHILE LIKELY NOT A COMPLETE WASH OUT, THERE WILL BE PERIODIC
CHANCES FOR THUNDERSTORM THROUGH THE HOLIDAY WEEKEND.
DISCUSSION
ISSUED AT 202 AM CDT TUE JUN 30 2026
HAVE ELECTED TO UPGRADE CURRENT ADVISORY TO AN EXTREME HEAT
WARNING, AND EXTENDED HEADLINES THROUGH THURSDAY BASED ON THE
POTENTIAL FOR A FOURTH DAY OF HOT AND HUMID CONDITIONS FOR MUCH
OF THE AREA.
AN UPPER LEVEL RIDGE, WITH H5 HEIGHTS ANALYZED ~5960 METERS,
WAS CENTERED JUST SOUTH OF THE OHIO VALLEY ACROSS KENTUCKY AND
TENNESSEE. THIS RIDGE IS FORECAST TO MAINTAIN ITS STRENGTH
ACROSS THE AREA THROUGH AT LEAST WEDNESDAY, BEFORE GRADUALLY
ELONGATING WEST TO EAST INTO THE MID-ATLANTIC REGION LATE IN THE
WEEK. NORTHWEST OF THE RIDGE AXIS, LOW AND MID-LEVEL
TEMPERATURES ARE PROGGED TO WARM SLIGHTLY TODAY, WITH 925MB
TEMPS IN THE +26/27C RANGE AND 700MB TEMPS AROUND +13C. THIS
WILL SUPPORT SURFACE TEMPS A BIT WARMER THAN ON MONDAY, WITH
MID-90S IN MANY LOCATIONS. FORECAST SOUNDINGS DEPICT A
SUBSIDENCE INVERSION IN THE 800-850MB RANGE, LIMITING THE MIXING
DEPTH DESPITE OTHERWISE BREEZY SOUTHWEST LOW-LEVEL FLOW. THIS,
LIKELY IN COMBINATION WITH INCREASING CROP EVAPOTRANSPIRATION,
RESULTED IN DEW POINTS SOMEWHAT HIGHER THAN EXPECTED MONDAY,
ESPECIALLY ACROSS THE SOUTHERN HALF OF THE FORECAST AREA WHERE
SOME UPPER 70S/80 DEGREE DEW POINTS WERE OBSERVED EVEN INTO THE
LATE AFTERNOON HOURS. EXPECTING SIMILAR TRENDS AGAIN TODAY,
SUPPORTING PEAK AFTERNOON HEAT INDICES IN THE 105-110 RANGE.
LATEST GUIDANCE CONTINUES TO INDICATE THAT MIXING MAY BE DEEPER
ON WEDNESDAY, POTENTIALLY LOWERING DEW POINTS BUT ALSO ALLOWING
SLIGHTLY WARMER AIR TEMPERATURES - WHICH WOULD MAINTAIN SIMILAR
PEAK HEAT INDICES.
MOST GUIDANCE THEN BEGINS TO SHIFT THE CENTER OF THE UPPER
RIDGE OFF TO THE EAST ACROSS THE APPALACHIANS AND MID-ATLANTIC
REGION BY THURSDAY. SLIGHT COOLING OF THE MID-LEVELS ESPECIALLY
INTO NORTHWEST AND FAR NORTHERN IL AND GRADUAL SOUTHEASTWARD
SHIFT OF THE UPPER JET AND STORM TRACK DOES SUGGEST AN
INCREASING THREAT OF CONVECTION SLIPPING INTO THE NORTHERN PARTS
OF THE FORECAST AREA, ESPECIALLY BY LATER THURSDAY AFTERNOON
AND EVENING. HOWEVER, A GOOD PORTION OF THE FORECAST AREA (OR
PERHAPS THE ENTIRE AREA IF CONVECTION DOESN'T MATERIALIZE UNTIL
LATER OR NOT AT ALL) WILL LIKELY SEE A FOURTH DAY OF HIGHS IN
THE LOW-MID 90S, MID-70S DEW POINTS AND PEAK HEAT INDICES AROUND
105. BASED ON THIS, AND IN COLLABORATION WITH NEIGHBORING WFOS
WILL UPGRADE CURRENT ADVISORY TO AN EXCESSIVE HEAT WARNING AND
WILL EXTEND ALL HEADLINES THROUGH THURSDAY EVENING.
GLOBAL ENSEMBLE GUIDANCE CONTINUES TO INDICATE THAT THE UPPER
RIDGE WILL CONTINUE TO DEAMPLIFY FRIDAY INTO THE INDEPENDENCE
DAY HOLIDAY WEEKEND. UNFORTUNATELY, THIS RESULTS IN WHAT LOOKS
TO BE A MORE ACTIVE STORM PATTERN FOR OUR REGION, AS A ZONAL JET
PATTERN DEVELOPS ACROSS THE NORTHERN CONUS WITH INDICATIONS OF
SEVERAL LOW-AMPLITUDE SHORT WAVES TRANSITING THE FLOW. WHILE
MANY DRY HOURS ARE LIKELY, AT LEAST PERIODIC THUNDERSTORM
POTENTIAL WILL EXIST FOR THE AREA THROUGH THE WEEKEND.
RATZER
AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 1230 PM CDT TUE JUN 30 2026
FORECAST CONCERNS INCLUDE...
GUSTY SOUTHWEST WINDS THIS AFTERNOON AND AGAIN WEDNESDAY.
POSSIBLE MVFR LEVEL CLOUDS WEDNESDAY MORNING.
A HIGH MVFR/LOW VFR BKN/OVC DECK HAS DEVELOPED ACROSS NORTHERN
IL LATE THIS MORNING AND WILL CONTINUE TO SLOWLY LIFT TO VFR
SHORTLY, AND IS THEN EXPECTED TO SCATTER OUT THROUGH THE
MID/LATE AFTERNOON. ANOTHER PERIOD OF MVFR LEVEL CLOUDS IS
POSSIBLE WEDNESDAY MORNING, SIMILAR TO THE PAST TWO MORNINGS.
CONFIDENCE IS LOW AND FOR NOW HAVE OPTED TO INCLUDE SCATTERED
MENTION FOR THIS POSSIBILITY.
SOUTHWEST WINDS WILL REMAIN GUSTY THIS AFTERNOON BUT THE HIGHEST
GUSTS APPEAR MOST LIKELY DURING THE MID/LATE AFTERNOON AND THEN
SPEEDS/GUSTS WILL DIMINISH WITH SUNSET THOUGH PERIODIC GUSTS
WILL REMAIN POSSIBLE FOR THE CHICAGO TERMINALS TONIGHT. GUSTS
WILL INCREASE BACK INTO THE LOWER/MID 20KT RANGE WEDNESDAY
MORNING. CMS
CLIMATE
ISSUED AT 1249 AM CDT TUE JUN 30 2026
.DAILY RECORDS FOR THE UPCOMING WEEK........
CHICAGO (KORD)
RECORD HIGH RECORD WARM MINIMUM
JUNE 30 99 (1953) 80 (2018)
JULY 1 103 (1956) 78 (1931)
JULY 2 99 (1970) 79 (1911)
JULY 3 102 (1949) 78 (1911)
JULY 4 102 (2012) 80 (1921)
ROCKFORD (KRFD)
RECORD HIGH RECORD WARM MINIMUM
JUNE 30 102 (1931) 76 (2018)
JULY 1 101 (1931) 76 (1970)
JULY 2 99 (1910) 74 (1970)
JULY 3 99 (1925) 75 (2012)
JULY 4 102 (2012) 77 (1977)
NWS CHICAGO
LOT WATCHES/WARNINGS/ADVISORIES
IL...EXTREME HEAT WARNING UNTIL MIDNIGHT CDT THURSDAY NIGHT FOR
ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.
IN...EXTREME HEAT WARNING UNTIL MIDNIGHT CDT /1 AM EDT/ THURSDAY
NIGHT FOR INZ001-INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY UNTIL 9 PM CDT THIS EVENING FOR WINTHROP
HARBOR IL TO GARY IN.
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