879
FXUS63 KLOT 291724
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1224 PM CDT MON JUN 29 2026
KEY MESSAGES
- DANGEROUS HEAT IS EXPECTED ACROSS THE AREA THIS WEEK WITH
AFTERNOON HEAT INDEX VALUES FORECASTED OVER 100 DEGREES.
LITTLE TO NO RELIEF IS EXPECTED AT THE LAKESHORE OR AT NIGHT.
- A RETURN TO A MORE ACTIVE PATTERN AND THUNDERSTORM CHANCES IS
LIKELY BY THE WEEKEND.
DISCUSSION
ISSUED AT 159 AM CDT MON JUN 29 2026
NO CHANGES MADE TO ONGOING HEAT HEADLINES, WITH AN EXTREME HEAT
WARNING FOR COOK COUNTY AND A HEAT ADVISORY FOR ALL OTHER
COUNTIES RUNNING FROM NOON TODAY THROUGH 10 PM CDT WEDNESDAY
EVENING.
EVENING UPPER AIR ANALYSIS DEPICTS AN UNSEASONABLY DEEP LONG-
WAVE UPPER TROUGH AND EMBEDDED CLOSED LOW OVER THE WESTERN
CONUS, AND DOWNSTREAM UPPER RIDGING FROM THE LOWER MISSISSIPPI
VALLEY INTO THE MIDWEST. AT THE SURFACE, DEEP LOW PRESSURE
AROUND 996 MB WAS OVER NORTHEAST COLORADO, WITH A WARM FRONT
ARCING INTO NORTHWEST IA AND THEN SOUTHEAST ALONG ROUGHLY A
KMLI-KCMI-KHUF LINE ACROSS CENTRAL ILLINOIS AND SOUTHWEST
INDIANA AS OF MIDNIGHT. THIS WARM FRONT IS EXPECTED TO LIFT
NORTH ACROSS THE WFO LOT FORECAST AREA THIS MORNING, AS THE
LOW DEVELOPS NORTH-NORTHEASTWARD ACROSS THE PLAINS IN RESPONSE
TO A STRONG MID-LEVEL SHORT WAVE ROUNDING THE BASE OF THE
AFOREMENTIONED UPPER LOW IN THE WEST.
MEANWHILE, THE UPPER RIDGE IS PROGGED TO BUILD NORTH-NORTHEAST
INTO THE OHIO VALLEY TODAY THROUGH WEDNESDAY, STRENGTHENING TO
NEARLY 6000 METERS. MODEL 850 MB TEMPERATURES OF +20/22C TODAY
AND +23/25C ACROSS THE FORECAST AREA TUESDAY AND WEDNESDAY WILL
SUPPORT UNSEASONABLY WARM SURFACE TEMPERATURES IN THE LOWER AND
MIDDLE 90S (PERHAPS A FEW UPPER 90S IN SPOTS), AS WELL AS
RELATIVELY STRONG CAPPING WITH 700 MB TEMPERATURES +12C OR
HIGHER. DESPITE THE STRENGTH OF THIS CAPPING INVERSION, BREEZY
SOUTHWEST LOW-LEVEL FLOW AND DRY AIR ALOFT IS LIKELY TO AID IN
MIXING OUT DEW POINTS DURING THE WARMEST PARTS OF EACH DAY, WITH
GUIDANCE GENERALLY INDICATING MID-70S AFTERNOON TD VALUES
(SLIGHTLY LOWER ACROSS THE URBANIZED CHICAGO METRO AREA).
FORECAST PEAK HEAT INDICES THEREFORE REMAIN AROUND 105 OR JUST A
BIT HIGHER FOR THE MOST PART.
WITH THE RELATIVELY WARM MID-LEVEL TEMPERATURES AND ASSOCIATED
CAPPING, THE MAIN AXIS OF THUNDERSTORM POTENTIAL TODAY THROUGH
WEDNESDAY IS EXPECTED TO REMAIN NORTHWEST OF THE FORECAST AREA
ACROSS PARTS OF IA/MN AND WI. SOME GUIDANCE DOES INDICATE THAT
CONVECTIVE COMPLEXES WILL OCCUR TO OUR NORTHWEST BOTH TONIGHT
AND TUESDAY NIGHT, WHICH COULD PUSH DECAYING CONVECTION, OR MORE
LIKELY, ASSOCIATED OUTFLOW BOUNDARIES INTO NORTHERN IL DURING
THE EARLY PARTS OF BOTH TUESDAY AND WEDNESDAY. WHILE THESE
OUTFLOWS COULD POTENTIALLY IMPACT HEAT INDICES AND WOULD NEED TO
BE MONITORED, THE BREEZY SOUTHWEST FLOW ACROSS THE REGION WOULD
MOST LIKELY MIX OUT THE EFFECTS ON SURFACE TEMPS/DEW POINTS
DURING THE DAY.
BY THURSDAY AND FRIDAY, THE CENTER OF THE UPPER RIDGE IS
FORECAST TO SHIFT SLIGHTLY SOUTHEAST ACROSS KENTUCKY AND
TENNESSEE, FLATTENING ACROSS THE UPPER MIDWEST AND GREAT LAKES
REGIONS AS THE WESTERN CONUS UPPER LOW LIFTS OUT ACROSS ONTARIO.
COOLER MID-LEVEL TEMPS RESULT IN WEAKER CAPPING ACROSS THE
UPPER MIDWEST, AND INCREASE THE LIKELIHOOD OF THUNDERSTORM
COMPLEXES (OR THEIR REMAINS) WORKING INTO THE FORECAST AREA AT
TIMES. WHILE STILL WARM AND MUGGY EVEN INTO NEXT WEEKEND, PEAK
DAYTIME HEAT INDICES ARE FORECAST MORE IN THE 90S TO AROUND 100
DEGREE RANGE EVEN WITHOUT ACCOUNTING FOR DIRECT IMPACTS OF
STORMS OR CONVECTIVE OUTFLOWS. THUS THE TIMING OF CURRENT HEAT
HEADLINES, WHICH RUN THROUGH WEDNESDAY EVENING, CONTINUES TO
LOOK VERY REASONABLE. IN FACT, OVER THE WEEKEND, CURRENT
GUIDANCE AND ENSEMBLES EVENTUALLY FLATTEN/BREAK DOWN THE RIDGE
OVER THE SOUTHEASTERN U.S., AND INDICATE A RETURN TO A
POTENTIALLY MORE ACTIVE (STORM-WISE), ZONAL JET PATTERN.
RATZER
AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1224 PM CDT MON JUN 29 2026
ONLY FORECAST CONCERN THIS PERIOD ARE THE WINDS. SOUTH/
SOUTHWEST WINDS HAVE BEEN SLOW TO INCREASE LATE THIS MORNING
INTO EARLY THIS AFTERNOON BUT GUSTS INTO THE LOWER/MID 20KT
RANGE ARE STILL EXPECTED THIS AFTERNOON. DIRECTIONS WILL TURN
MORE SOUTHERLY WITH SUNSET THIS EVENING AND GUSTS INTO THE
15-20KT RANGE WILL BE POSSIBLE OVERNIGHT, MAINLY ACROSS THE
URBAN CHICAGO AREA WHERE TEMPS WILL BE WARMER. LOW LEVEL WINDS
WILL STEADILY INCREASE OVERNIGHT AND LOW LEVEL WIND SHEAR WILL
BE POSSIBLE, MAINLY WEST OF THE CHICAGO TERMINALS. DIRECTIONAL
CHANGES IN THE LOW LEVELS MAY BE MORE OF A CONCERN THAN THE
SPEEDS AND LOW LEVEL WIND SHEAR MENTION WILL NEED TO BE
MONITORED WITH LATER FORECASTS. SOUTHWEST WINDS WILL INCREASE
MID/LATE TUESDAY MORNING, BACK INTO THE LOWER/MID 20KT RANGE.
THERE IS SOME POTENTIAL FOR WIND GUSTS INTO THE 30KT RANGE BY
LATE TUESDAY AFTERNOON.
EARLIER IFR/LOW MVFR CIGS HAVE STEADILY LIFTED WITH SOME HIGH
MVFR CIGS STILL POSSIBLE FOR THE NEXT 1-2 HOURS, BUT OVERALL
EXPECTING PREVAILING VFR CIGS THAT WILL SCATTER OUT LATER THIS
AFTERNOON. THE LOW LEVELS WILL REMAIN QUITE MOIST OVERNIGHT INTO
TUESDAY MORNING AND NOT EXPECTING ANOTHER PERIOD OF LOWER CIGS
TUESDAY MORNING, BUT TRENDS WILL NEED TO BE MONITORED. CMS
CLIMATE
ISSUED AT 252 AM CDT SUN JUN 28 2026
.DAILY RECORDS FOR THE UPCOMING WEEK........
CHICAGO (KORD)
RECORD HIGH RECORD WARM MINIMUM
JUNE 29 97 (1954) 80 (1931)
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 29 103 (1931) 75 (1931)
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...HEAT ADVISORY UNTIL 10 PM CDT WEDNESDAY FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ106-ILZ107-
ILZ108.
EXTREME HEAT WARNING UNTIL 10 PM CDT WEDNESDAY FOR ILZ103-
ILZ104-ILZ105.
IN...HEAT ADVISORY UNTIL 10 PM CDT /11 PM EDT/ WEDNESDAY FOR INZ001-
INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY UNTIL 10 PM CDT THIS EVENING FOR THE IL
NEARSHORE WATERS.
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