786
FXUS63 KLOT 250523
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1223 AM CDT WED JUN 25 2025
KEY MESSAGES
- SCATTERED SHOWERS AND STORMS WILL MOVE ACROSS THE AREA
OVERNIGHT INTO WEDNESDAY MORNING, WITH MORE ISOLATED COVERAGE
EXPECTED ON 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 /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 1223 AM CDT WED JUN 25 2025
KEY MESSAGES FOR THE 06Z TAF PERIOD INCLUDE:
* INTERMITTENT SHOWERS AND POSSIBLY SOME THUNDERSTORMS THROUGH
THE NIGHT AND INTO WEDNESDAY MORNING, WITH A LESSER CHANCE
DURING THE AFTERNOON AND EVENING.
* A PERIOD OF MVFR CIGS EXPECTED WEDNESDAY MORNING
THE SCATTERED SHOWERS AND STORMS WE SAW EARLIER THIS EVENING
HAVE MOVED AWAY FROM THE TAF SITES, BUT MORE ARE ON THE WAY FROM
THE WEST. IT'S UNCLEAR WHETHER THE STORMS WILL BE ABLE TO HOLD
TOGETHER OR IF WE'LL END UP WITH ONLY SHOWERS, BUT THE PRECIP
LOOKS TO ARRIVE AT THE CHICAGO SITES AROUND 09Z. IT LOOKS LIKE
IT MIGHT SCOOT JUST SOUTH OF RFD WHERE THE LESSER LIKELIHOOD WAS
TREATED WITH A VCSH THROUGH THE NIGHT. COVERAGE WILL BECOME
MORE ISOLATED THROUGH THE MORNING WITH THE BULK OF THE AFTERNOON
EXPECTED TO BE DRY, ALTHOUGH A POP UP SHOWER OR STORM WILL
REMAIN POSSIBLE THROUGH THE END OF WEDNESDAY.
IN OTHER NEWS, A PERIOD OF MVFR CIGS IS LIKELY DURING THE
MORNING HOURS, ALTHOUGH POSSIBLY MOVING OVERHEAD AS EARLY AS
AROUND 09Z. LIGHT NE WINDS TONIGHT MAY GO VARIABLE IN THE
VICINITY OF SHOWERS AND STORMS. EXPECT NE WINDS BETWEEN 5 AND 10
KT DURING THE DAY ON WEDNESDAY GOING LIGHT AND SSW EARLY
OVERNIGHT.
DOOM
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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