858
FXUS63 KLOT 290543
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1243 AM 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.
DISCUSSION
ISSUED AT 125 PM CDT SUN JUN 28 2026
A COMPLEX OF SHOWERS AND THUNDERSTORMS IS PROGRESSING EASTWARD
THROUGH NORTHEAST IOWA AT THE TIME THE DISCUSSION WAS PUBLISHED.
THE CURRENT EXPECTATION IS FOR IT TO FOLLOW A NORTHWEST TO
SOUTHEAST INSTABILITY GRADIENT ACROSS NORTHERN ILLINOIS. BUT AS
THE UPPER LEVEL RIDGE PATTERN IS AMPLIFYING AND ADVECTING IN
WARMER TEMPERATURES IN THE MID LEVELS, THERE IS LOWER CONFIDENCE
IN THUNDERSTORMS BEING ABLE TO MAINTAIN THEIR STRENGTH. PERHAPS
THERE IS LOWER CONFIDENCE IN THE EASTWARD EXTENT OF THE
LIGHTNING ACTIVITY, BUT CURRENTLY PROJECTING THE SYSTEM TO DECAY
AS IT APPROACHES THE FOX VALLEY WITH ONLY ISOLATED EMBEDDED
THUNDERSTORMS. LOCALIZED SMALL HAIL IS STILL POSSIBLE, MAINLY
WEST OF THE FOX VALLEY, DUE TO OVER 40 KNOTS OF EFFECTIVE SHEAR
AVAILABLE. OTHERWISE, GUSTY WINDS ARE POSSIBLE WITH ANY SHOWER
OR THUNDERSTORM. HOWEVER, AS THIS COMPLEX OF SHOWERS PASSES
EAST, AN AREA OF LOCALIZED LOW PRESSURE IS EXPECTED TO DEVELOP
IN ITS WAKE. SOUTHEAST WIND GUSTS UNRELATED TO SHOWERS AND
THUNDERSTORMS HAVE THE POTENTIAL TO INCREASE LATE THIS
AFTERNOON/EARLY EVENING FOR AN HOUR OR TWO UP TO 40 MPH.
AS AN ANOMALOUSLY DEEP LOW CONTINUES TO SIT OVER THE
INTERMOUNTAIN WEST, ANOTHER EMBEDDED IMPULSE IS EXPECTED TO
MOVE NORTHEASTWARD INTO WISCONSIN. THIS MAY TRIGGER SOME
SCATTERED LIGHT SHOWERS OR SPRINKLES AROUND DAYBREAK, MAINLY FOR
AREAS CLOSER TO THE WISCONSIN STATELINE AND THE LAKE MICHIGAN
SHORELINE. BUT ANY MOISTURE IS GOING TO HAVE TO CONTEND WITH THE
GROWING DRY AIR MASS, PREVENTING ANY FORMAL MENTION OF PRECIP
IN THE POPS FORECAST. MORE INTRIGUING IS THAT HIGH-RES GUIDANCE
IS NOW SUGGESTING AN MCS COULD DEVELOP TOMORROW OFF THIS IMPULSE
IN NORTHERN WISCONSIN AND HEAD TOWARD MICHIGAN. IF AN MCS WERE
TO OCCUR, THERE IS A CHANCE THAT SOME OUTFLOW COULD RACE
SOUTHWESTWARD TOWARD ARE AREA, BUT THE CURRENT GUIDANCE IS THAT
THE MCS TACK WOULD BE FAR ENOUGH EAST TO NOT IMPACT OUR AREA.
OTHERWISE, THE MAIN STORY REMAINS THE HEAT WAVE. AN AMPLIFIED
UPPER LEVEL RIDGE OVER THE AREA WILL SET UP PREVAILING SOUTHWEST
WINDS, A DRIER AIR MASS, AND HIGHER SURFACE PRESSURE. THE
SOUTHWEST FLOW WILL INCREASE 850 MB TEMPERATURES NORTH OF 20C
AND PULL 70+ DEWPOINTS ACROSS THE FORECAST AREA. HOT AND HUMID
CONDITIONS ARE FORECAST STARTING TOMORROW THROUGH AT LEAST
WEDNESDAY. BASED ON CURRENT GUIDANCE, HEAT INDICES ARE EXPECTED
UP TO AROUND 105F. THERE'S FAIRLY GOOD CONFIDENCE THAT 110F (THE
CRITERIA FOR AN EXTREME HEAT WARNING) WILL NOT BE REACHED.
THEREFORE, NO CHANGES WERE PRESENTLY MADE TO THE HEAT ADVISORY,
THOUGH CANNOT RULE OUT UPGRADING IT TO A WARNING IF THE HEAT IS
EXPECTED TO CONTINUE THROUGH THURSDAY (MORE ON THAT IN A
MINUTE). OTHERWISE, THE EXTREME HEAT WATCH FOR COOK COUNTY (WITH
ITS LOWER HEAT CRITERIA) WAS CONVERTED TO AN EXTREME HEAT
WARNING GIVEN THE CONFIDENCE IN THE HEAT FOR MONDAY THROUGH
WEDNESDAY.
ALL THE UNCERTAINTY ON THE DURATION OF THE HEAT WAVE FOCUSES ON
THE STRENGTH AND LOCATION OF THE RIDGE OVER THE EASTERN CONUS.
MODELS HAVE BEEN BOUNCING AROUND A LOT OVER THE LAST SEVERAL
RUNS. THE STRONGER THE RIDGE LATE IN THE WEEK, THE BETTER
CHANCES FOR HIGHER HEAT INDICES TO REMAIN IN PLACE AND THE
POTENTIAL FOR THAT UPGRADE FROM THE ADVISORY TO A WARNING.
HOWEVER, A WEAKER RIDGE AND/OR A DRIFT FARTHER EAST WOULD LEAD
OPEN THE DOOR FOR CONVECTIVE SYSTEMS TO PASS CLOSER TO THE AREA
WHICH COULD HELP GIVE "SOME" HEAT RELIEF. GIVEN THE UNCERTAINTY
AND MODEL DISAGREEMENT, FELT NO NEED TO CHANGE ANY OF THE CHANCE
POPS IN THE EXTENDED FORECAST THOUGH IT IS ACCOMPANIED WITH
LOWER CONFIDENCE. ONE LAST NOTE, DESPITE THE MODEL DISAGREEMENT
ON THE RIDGE PLACEMENT BOTH THE GEFS AND EURO ENSEMBLES ARE
KEEPING 850 MB AROUND 20C THROUGH THE END OF THE WEEK AND
WEEKEND. SO EVEN IF HEAT INDEX VALUES WERE TO FALL AT THE END OF
THE WEEK BELOW AN ADVISORY OR WARNING CRITERIA, THEY COULD
STILL REMAIN WELL INTO THE 90S THROUGH THE HOLIDAY WEEKEND.
WELCOME TO SUMMER, EVERYONE!
DK
AVIATION /06Z TAFS THROUGH 12Z TUESDAY/
ISSUED AT 1243 AM CDT MON JUN 29 2026
AN AXIS OF LOW-LEVEL MOISTURE SOUTHWEST OF THE TERMINALS EARLY
THIS MORNING WILL LIFT NORTHEAST OVER THE NEXT SEVERAL HOURS.
PERIODS OF BKN MVFR CEILINGS ARE LIKELY DURING THIS TIME.
OTHERWISE, VFR CONDITIONS ARE EXPECTED THROUGH TONIGHT.
SE/SSE WINDS UP TO AROUND 10 KNOTS EARLY THIS MORNING WILL
GRADUALLY VEER SSW THROUGH 12Z. WINDS WILL THEN REMAIN SSW/SW
THROUGH THE TONIGHT, WITH GUSTS TO 20 KNOTS IN THE MORNING AND
AROUND 25 KNOTS DURING THE AFTERNOON. THOUGH SURFACE WINDS WILL
DIMINISH AFTER SUNSET, A 40 TO 45 KNOT LOW-LEVEL JET LATE THIS
EVENING AND OVERNIGHT WILL EITHER PRODUCE SPORADIC SURFACE GUSTS
TO AROUND 20 KNOTS OR LEAD TO LLWS. EXPECTATION IS THAT SOME
GUSTS WILL PERSIST AT ORD/MDW DUE TO WEAKER NEAR SURFACE
STABILITY OVER THE URBAN HEAT ISLAND. HOWEVER, HAVE INCLUDED
LLWS AT RFD WHERE THE JET WILL BE SLIGHTLY STRONGER BY LATE
EVENING. WILL LIKELY NEED TO ADD THIS TO DPA/GYY FOR THE NEXT
TAF CYCLE.
KLUBER
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 FROM NOON TODAY TO 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 FROM NOON TODAY TO 10 PM CDT WEDNESDAY
FOR ILZ103-ILZ104-ILZ105.
IN...HEAT ADVISORY FROM NOON CDT /1 PM EDT/ TODAY TO 10 PM CDT /11
PM EDT/ WEDNESDAY FOR INZ001-INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY FROM NOON TODAY TO 10 PM CDT THIS EVENING
FOR THE IL NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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