631
FXUS63 KLOT 030833
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
333 AM CDT FRI JUL 3 2026
KEY MESSAGES
- HOT AND HUMID CONDITIONS WILL CONTINUE TODAY, THOUGH THE
HIGHEST HEAT INDICES (UP TO/AROUND 105F) WILL LIKELY FOCUS
NEAR/SOUTH OF THE KANKAKEE RIVER. ON INDEPENDENCE DAY, PEAK
HEAT INDICES OF ~95-100F ARE EXPECTED NEAR AND SOUTH OF I-80.
- WAVES OF THUNDERSTORMS ARE EXPECTED THROUGH THE WEEKEND,
THOUGH THERE WILL BE MANY DRY HOURS. ANY STORMS TODAY WILL BE
CAPABLE OF PRODUCING DAMAGING WINDS. THERE WILL ALSO BE A
THREAT FOR LOCALIZED FLASH FLOODING WITH ANY FOCUSED CORRIDORS
OF STORMS THROUGH THE WEEKEND.
DISCUSSION
ISSUED AT 333 AM CDT FRI JUL 3 2026
EARLIER STORMS HAVE EXITED THE AREA TO THE EAST WITH THE
ASSOCIATED OUTFLOW BOUNDARY HAVING MANAGED TO PUSH AS FAR SOUTH
AS PAXTON, IL BRINGING TEMPERATURES INTO THE LOWER 70S
AREAWIDE. WHILE A STRAY SHOWER OR STORM CAN'T BE RULED OUT
OVERNIGHT, MOST AREAS ARE EXPECTED TO REMAIN DRY.
THE RESIDUAL OUTFLOW BOUNDARY FROM STORMS EARLY THIS MORNING
IS ANTICIPATED TO LIFT BACK TO THE NORTH SOME THOUGH EXACTLY
WHERE REMAINS UNCERTAIN. OPTED TO MAINTAIN THE EXTREME HEAT
WARNING FOR COUNTIES ALONG AND SOUTH OF THE KANKAKEE RIVER
VALLEY, WHERE HEAT INDICES MAY REACH 105 DEGREES THIS
AFTERNOON. FARTHER NORTH WILL STILL BE HOT AND HUMID, BUT NOT TO
THE EXTENT OF THE PAST SEVERAL DAYS WITH FORECAST PEAK HEAT
INDICES IN THE 95-100 DEGREE RANGE.
THE SHOWER AND THUNDERSTORM POTENTIAL TRENDS FOR TODAY ARE ALSO
UNCERTAIN, AS IS OFTEN THE CASE IN THESE TYPES OF PATTERNS.
FIRST, WE ARE MONITORING STORMS OVER NORTHEAST NEBRASKA INTO
CENTRAL IOWA ONGOING EARLY THIS MORNING. THIS FEATURE IS
EXPECTED TO PROGRESS EAST WITH TIME, LIKELY IN A WEAKENING
STATE. HOWEVER, AN MCV APPEARS TO BE DEVELOPING ACROSS NORTHWEST
IOWA WHICH, PAIRED WITH A LIKELY CONVECTIVELY AUGMENTED MID-
LEVEL VORT, MAY SERVE AS A FORCING MECHANISM FOR SHOWER AND
THUNDERSTORM DEVELOPMENT INTO NORTHERN ILLINOIS IN THE
AFTERNOON. ADDITIONALLY, THE AFOREMENTIONED OUTFLOW BOUNDARY MAY
SERVE AS A FORCING MECHANISM FOR SHOWER AND THUNDERSTORM
DEVELOPMENT IN THE AFTERNOON. AGAIN, QUESTIONS REMAIN AS TO
EXACTLY HOW FAR NORTH THE BOUNDARY WILL LIFT THIS AFTERNOON. IT
IS TOUGH TO SAY WHETHER THE LATE EVENING TIMEFRAME WILL BE
SHOWER AND STORM FREE GIVEN THE POTENTIAL FOR ADDITIONAL
REDEVELOPMENT ALONG ANY POTENTIAL RESIDUAL OUTFLOW BOUNDARIES
FROM ANY STORMS THAT DEVELOP EARLIER IN THE DAY. WHILE SHEAR IS
NOT ESPECIALLY STRONG, AMPLE INSTABILITY IN PLACE WILL BE
SUPPORTIVE OF DAMAGING WIND GUSTS WITH ANY STORMS TODAY/TONIGHT.
ANY TRAINING CORRIDORS OF STORMS COULD ALSO LEAD TO FLOODING.
GOING FORWARD INTO INDEPENDENCE DAY, A LARGER DISTURBANCE IS
FORECAST TO MOVE ACROSS THE REGION BRINGING ANOTHER ROUND OF
SHOWERS AND STORMS, CURRENTLY FAVORING THE AFTERNOON TO EARLY
EVENING TIMEFRAME. THE NORTHERN PERIPHERY OF THE BETTER
INSTABILITY WILL LIKELY HAVE SHIFTED SOUTH SOME IN RESPONSE TO
THE FRIDAY/FRIDAY NIGHT ROUNDS OF STORMS. STILL CAN'T RULE OUT
LOCALLY STRONG TO DAMAGING WIND GUSTS WITH ANY STORMS THAT DO
DEVELOP, WITH PERHAPS A LOCALLY HIGHER THREAT SOUTH OF I-80.
WHILE IT IS IMPORTANT TO NOT LATCH ONTO ANY ONE MODEL RUN, IT IS
WORTH NOTING THAT THE LATEST HRRR (6Z) ATTEMPTS TO DEVELOP MORE
ROBUST STORMS NORTH OF I-80 ON SATURDAY AS THE WAVE MOVES
THROUGH (LIKELY OWING TO FARTHER NORTH POSITION OF EARLIER
ROUNDS OF CONVECTION). ACCORDINGLY, THE MESSAGE WILL REMAIN THAT
ADDITIONAL ROUNDS OF STORMS CAN BE EXPECTED (SOME POTENTIALLY
STRONG TO LOCALLY SEVERE).
SUNDAY WILL FEATURE YET ANOTHER MID-LEVEL WAVE MOVING ACROSS THE
REGION DUE TO THE FLATTENING OF THE UPPER RIDGE. THIS WILL BRING
ADDITIONAL ROUNDS OF SHOWERS AND ISOLATED EMBEDDED (NON-SEVERE)
STORMS WITH GREATEST COVERAGE FAVORED IN THE AFTERNOON-EARLY
EVENING. TEMPERATURES WILL BE CLOSER TO NORMAL FOR EARLY JULY
WITH HIGHS IN THE LOWER TO MID 80S.
BEYOND THE WEEKEND THE UPPER RIDGE BEGINS TO BUILD BACK NORTH
SLIGHTLY WITH THE EMBEDDED WAVES MOVING TO OUR NORTH. MEANWHILE
ANOTHER WAVE (OR WAVES) WILL MOVE WITHIN THE RIDGE TO OUR SOUTH
(AND POTENTIALLY STALL OUT). OVERALL THIS FAVORS SHOWER/STORM
COVERAGE FOCUSING MAINLY NORTH OR SOUTH OF THE AREA INTO MID-
WEEK. SHOWER AND STORM CHANCES RETURN LATER IN THE WEEK AS THE
RIDGE BEGINS TO BREAK DOWN AGAIN.
PETR
AVIATION /06Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 1227 AM CDT FRI JUL 3 2026
FORECAST CONCERNS FOR THE TERMINALS...
- LINE OF THUNDERSTORMS TO IMPACT THE CHICAGO AREA TERMINALS
THROUGH THE EARLY OVERNIGHT HOURS. A FEW STORMS MAY PRODUCE
GUSTY WINDS IN EXCESS OF 35 KTS AND HEAVY DOWNPOURS RESULTING
IN IFR VISIBILITY.
- ANOTHER PERIOD OF SHOWERS AND THUNDERSTORMS ARE POSSIBLE
FRIDAY AFTERNOON ESPECIALLY NEAR AND SOUTH OF A VYS TO VPZ
LINE.
A LINE OF THUNDERSTORMS CONTINUES TO TRAIN ACROSS PORTIONS OF
NORTHEAST IL AND IS EXPECTED TO PERSIST THROUGH THE EARLY
OVERNIGHT HOURS. BASED ON THE ORIENTATION OF THE LINE, THE MAIN
TERMINALS TO BE IMPACTED BY THESE STORMS ARE ORD, DPA, AND MDW
BUT CANNOT RULE OUT A FEW STORMS NEARING GYY AFTER 07-08Z. WHILE
MOST OF THESE STORMS HAVE BEEN MAINLY HEAVY RAIN PRODUCERS
(RESULTING IN IFR VISIBILITIES), A FEW HAVE PRODUCED GUSTY WINDS
IN EXCESS 35 KTS. AFTER 08-09Z THE LINE OF STORMS SHOULD BEGIN
TO WEAKEN AS INSTABILITY GETS USED UP, BUT CONFIDENCE IS LOW ON
THE EXACT TIME THESE SHOWERS/STORMS WILL SUBSIDE. ADDITIONALLY,
THERE IS ANOTHER CLUSTER OF SHOWERS AND STORMS IN NORTHERN IA
THAT COULD MOVE INTO NORTHWEST IL TOWARDS THE PREDAWN HOURS.
GIVEN THAT INSTABILITY LOCALLY SHOULD BE USED UP BY THAT TIME
SUSPECT THE IA ACTIVITY SHOULD WEAKEN PRIOR TO REACHING RFD, BUT
HAVE MAINTAINED A VCSH MENTION THERE OVERNIGHT DUE TO LOWER
CONFIDENCE.
OUTSIDE OF THE SHOWER/STORMS TONIGHT, WEST-SOUTHWEST WINDS
AROUND 10-12 KTS CAN BE EXPECTED OVERNIGHT AND THROUGH THE DAY
ON FRIDAY WITH OTHERWISE VFR CONDITIONS. HOWEVER, THERE IS
ANOTHER CHANCE FOR SHOWERS AND THUNDERSTORMS FRIDAY AFTERNOON
AND EVENING. LATEST GUIDANCE TRENDS INDICATE THAT THE FAVORED
ZONE FOR SHOWER/STORMS ON FRIDAY WILL BE NEAR AND SOUTH OF THE
OUTFLOW BOUNDARY FROM TONIGHT'S STORMS. WHILE THE EXACT LOCATION
OF THIS BOUNDARY IS LOW CONFIDENCE, THE GENERAL CONSENSUS IS
THAT THE BOUNDARY SHOULD BE NEAR A VYS TO VPZ LINE. FOR NOW HAVE
OPTED TO MAINTAIN THE PROB30S AT ALL TAF SITES FOR THIS
POTENTIAL BUT SUSPECT THE SOME SITES COULD MISS OUT ON MOST OF
THE THUNDERSTORM ACTIVITY. THAT SAID, WHERE STORMS DO DEVELOP ON
FRIDAY EXPECT A THREAT FOR GUSTY WINDS AND HEAVY DOWNPOURS TO
ACCOMPANY THEM.
FINALLY, THERE IS ALSO A SIGNAL FOR ANOTHER CLUSTER OF SHOWERS
AND STORMS TO MOVE INTO THE AREA LATE FRIDAY NIGHT INTO SATURDAY
MORNING. GIVEN THE UNCERTAINTY IN HOW THE AFTERNOON STORMS WILL
IMPACT THE ENVIRONMENT AND THE LATE ARRIVAL TIME (AFTER THE
CONCLUSION OF THE 30-HOUR TAFS) HAVE LEFT DRY CONDITIONS TO
CONCLUDE THE TAFS FOR NOW.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...EXTREME HEAT WARNING UNTIL 7 PM CDT THIS EVENING FOR ILZ023-
ILZ032-ILZ033-ILZ039.
IN...EXTREME HEAT WARNING UNTIL 7 PM CDT /8 PM EDT/ THIS EVENING
FOR INZ010-INZ011-INZ019.
LM...NONE.
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