205
FXUS63 KLOT 242000
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
300 PM CDT TUE JUN 24 2025
KEY MESSAGES
- SCATTERED SHOWERS AND THUNDERSTORMS ARE FAVORED SOUTH OF I-55
THROUGH THIS EVENING. A LOW THREAT FOR LOCALIZED DAMAGING WIND
GUSTS EXISTS, WITH A LOCALIZED FLOODING THREAT PERSISTING
OVERNIGHT INTO WEDNESDAY.
- PEAK AFTERNOON HEAT INDICES WILL STILL BE IN THE UPPER 90S TO
NEAR 100 THROUGH MUCH OF THE WEEK.
- PERIODIC SHOWER AND STORM CHANCES EXIST THROUGH EARLY NEXT
WEEK WITH MANY DRY HOURS IN BETWEEN ROUNDS. THE STRONGEST
STORMS MAY BE CAPABLE OF LOCALIZED DAMAGING WINDS AND FLASH
FLOODING.
DISCUSSION
ISSUED AT 255 PM CDT TUE JUN 24 2025
THROUGH WEDNESDAY:
IT IS ANOTHER HOT AND HUMID DAY INLAND, MEANWHILE AN OUTFLOW
BOUNDARY COMBINED WITH THE LAKE BREEZE HAS HELPED TO BRING
RELIEF TO LAKE AND COOK COUNTY. BEHIND THESE BOUNDARIES THE
ATMOSPHERE IS MUCH MORE STABLE. WE ARE IN BETWEEN SHORTWAVES,
AND THUS THE MAIN FORCING TO HAVE A BIT MORE ROBUST CUMULUS AND
THUNDERSTORM DEVELOPMENT HAVE BEEN ALONG AND AHEAD OF THESE
BOUNDARIES IN AN ENVIRONMENT THAT HAS OVER 2000 J/KG OF CAPE.
EXPECT CONTINUED SHOWER DEVELOPMENT ALONG WITH ISOLATED TO
WIDELY SCATTERED THUNDERSTORMS, WITH THESE BEING MORE LIKELY
CONFINED SOUTH OF I-55, INCLUDING SOUTHERN COOK COUNTY AND THEN
INTO NW INDIANA.
ADDITIONAL SHORTWAVE ACTIVITY WILL SPREAD FROM IOWA INTO
NORTHERN ILLINOIS THIS EVENING. THIS WILL LIKELY BRING SOME
UPTICK IN SHOWER ACTIVITY. WE DO ANTICIPATE THAT THIS WAVE MAY
TRIGGER SOME ADDITIONAL THUNDERSTORM ACTIVITY THIS EVENING,
FAVORED WEST AND THEN POSSIBLY ALONG AND SOUTH OF I-80 AHEAD OF
ANY LINGERING BOUNDARIES FROM THIS AFTERNOON.
THE FLOW WILL TURN MORE WESTERLY AND PARALLEL TO THE LINGERING
BOUNDARIES, AND THUS WE WILL WANT TO WATCH FOR ANY LOCALIZED
AREAS OF HEAVY RAINFALL, LATER TONIGHT INTO EARLY WEDNESDAY.
CONFIDENCE ON WEDNESDAY AFTERNOON ACTIVITY IS LOW, AS IT IS
CONCEIVABLE THAT THE MAIN FORCING SHIFTS NE OF THE AREA, AND
THERE WILL BE ONSHORE FLOW THAT WOULD CONFINE ANY SCATTERED
DEVELOPMENT TO INLAND AREAS. IT WILL BE A SIGNIFICANTLY MORE
COMFORTABLE DAY FOR AREAS NEAR THE LAKE, THOUGH IT WILL STILL BE
WARM AND HUMID INLAND.
KMD
WEDNESDAY NIGHT THROUGH TUESDAY:
THE UPPER LEVEL RIDGE IS EXPECTED TO CONTINUE TO FLATTEN
THROUGH MID- WEEK, AND BREAK DOWN AS IT SHIFTS EASTWARD INTO
FRIDAY. WHILE THIS OCCURS, A SERIES OF MAINLY LOW-AMPLITUDE MID-
LEVEL SHORT WAVES ARE EXPECTED TO TRACK ACROSS THE UPPER
MIDWEST AND GREAT LAKES REGION, WITH A QUASI-STATIONARY, WEST-
EAST ORIENTED FRONTAL BOUNDARY ACROSS THE AREA. THIS WILL SET
THE STAGE FOR PERIODIC SHOWER AND THUNDERSTORMS TO AFFECT THE
FORECAST AREA THROUGH THE WEEK, WITH GREATEST CHANCES FOCUSED
DURING PEAK DIURNAL HEATING/INSTABILITY OF THE AFTERNOON AND
EVENINGS. THERE REMAINS LOWER CONFIDENCE ON SPECIFIC TIMING OF
THESE SHORTER AMPLITUDE WAVES (OR MCVS GENERATED BY UPSTREAM
CONVECTION) AS MODELS OFTEN STRUGGLE WITH THEM.
THE AIR MASS ALONG AND SOUTH OF THE STATIONARY FRONTAL BOUNDARY
WILL REMAIN WARM, MOIST AND CONDITIONALLY UNSTABLE THROUGH THE
PERIOD. THE COLUMN REMAINS RELATIVELY WARM ALOFT, MAINTAINING
SOMEWHAT WEAK MID-LEVEL LAPSE RATES, WHILE THE CORE OF THE MID-
UPPER LEVEL JET STREAM STAYS LARGELY NORTH OF THE FORECAST AREA.
THE MODEST MID- LEVEL FLOW AND LAPSE RATES, COUPLED WITH PWATS
OVER 1.5 INCHES WOULD SUPPORT DIURNALLY STRONG THUNDERSTORMS
CAPABLE OF PRODUCING WET DOWNBURSTS, IN ADDITION TO THE THREAT
OF LOCALIZED FLOODING.
WHILE NOT AS HOT AND OPPRESSIVE AS THE PAST FEW DAYS HAVE BEEN,
IT WILL REMAIN SEASONABLY WARM AND HUMID THROUGH THE WEEK, WITH
DAYTIME HIGHS IN THE MID-80S TO LOWER 90S, WITH PEAK HEAT
INDICES AROUND 100 SOUTH OF THE FRONT. THERE WILL LIKELY BE SOME
DAYS WHERE ONSHORE WINDS OFF OF LAKE MICHIGAN PROVIDE SOME
COOLING NEAR THE SHORE, THOUGH THAT WILL LIKELY DEPEND ON THE
DAY TO DAY POSITION OF THE FRONTAL ZONE AND OUTFLOW BOUNDARIES.
AFTER THE RIDGE BREAKS DOWN, ZONAL FLOW IS EXPECTED TO DEVELOP
ALOFT OVER THE WEEKEND. MODELS ARE STARTING TO COME INTO BETTER
AGREEMENT WITH A LONG WAVE TROUGH DEVELOPING OVER ONTARIO AS A
RIDGE GOES OVER THE DESERT SOUTHWEST. THIS WILL ALLOW FOR
NORTHWEST FLOW TO DEVELOP OVER THE PLAINS AND BRING A RENEWED
CHANCE FOR SHOWERS AND THUNDERSTORMS INTO EARLY NEXT WEEK.
DK
AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 1251 PM CDT TUE JUN 24 2025
CONCERNS:
-SCATTERED SHOWERS AND THUNDERSTORMS ACROSS C90 AND INTO
NORTHWEST INDIANA FOCUSED THIS AFTERNOON
-HEAVY RAIN IN THE STRONGER STORMS
-LAKE BREEZE/OUTFLOW BOUNDARY WIND SHIFT
-TIMING ADDITIONAL WAVES OF SHOWERS AND STORMS THIS EVENING AND
AGAIN LATE TONIGHT INTO WEDNESDAY
THE LEAD SHORTWAVE THAT HAD THE MOST ORGANIZED FORCING HAS
SHIFTED INTO WISCONSIN, AND NOW THE MAIN FOCUS FOR THUNDERSTORMS
IS AN OUTFLOW BOUNDARY DRAPED FROM KVYS-KARR-KDPA-KPWK. THE
INTERACTION OF THIS BOUNDARY WITH THE LAKE BREEZE WILL LEAD TO
AN UPTICK IN SHOWER AND SCATTERED THUNDERSTORMS THIS AFTERNOON.
THE WINDOW FOR DPA FOR TS IS NARROW GIVEN THAT DPA IS ALONG THE
OUTFLOW, AND RFD SHOULD JUST SEE SOME -SHRA. THE FOCUS AREA WILL
BE THE CHICAGO TERMINALS AND INTO NW INDIANA. THESE SHOWERS AND
STORMS MAY REDUCE VISIBILITY TO IFR IN HEAVY RAIN.
THERE WILL LIKELY BE A LULL LATER AFTERNOON BEFORE ANOTHER WAVE
FROM IOWA WILL PUSH INTO ILLINOIS, AND INTERSECT WITH ANY
LINGERING BOUNDARIES. THERE COULD BE SOME TS WITH THIS, THOUGH
CONFIDENCE ON TIMING AND COVERAGE BEYOND THIS AFTERNOON ACTIVITY
IS SOMEWHAT LOW. THE SAME IS TRUE FOR LATE TONIGHT INTO
WEDNESDAY MORNING AS ANOTHER WAVE WILL TRIGGER ADDITIONAL SHRA
AND MAYBE SOME TS.
EXPECT WINDS AT ORD AND MDW AND MOST TERMINALS TO SHIFT NW
BEHIND THE OUTFLOW BOUNDARY BEFORE THE LAKE BREEZE/LAKE ENHANCED
BOUNDARY WILL MOVE THROUGH AND SHIFT WINDS TO NE.
KMD
LOT WATCHES/WARNINGS/ADVISORIES
IL...HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR ILZ023-ILZ032-
ILZ033-ILZ039.
IN...HEAT ADVISORY UNTIL 7 PM CDT /8 PM EDT/ THIS EVENING FOR
INZ010-INZ011-INZ019.
LM...NONE.
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