866
FXUS63 KLOT 241802
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
102 PM CDT TUE JUN 24 2025
KEY MESSAGES
- AFTERNOON HEAT INDICES OVER 100 ARE EXPECTED SOUTH OF I-80
AGAIN TODAY WHERE A HEAT ADVISORY REMAINS IN EFFECT.
- SCATTERED SHOWERS AND THUNDERSTORMS ARE ANTICIPATED LATER
TODAY INTO WEDNESDAY. A LOW THREAT FOR LOCALIZED DAMAGING WIND
GUSTS EXISTS THIS AFTERNOON AND EVENING, 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.
UPDATE
ISSUED AT 1033 AM CDT TUE JUN 24 2025
STILL CONCERNED ABOUT SOME HEAVY RAINFALL RATES THIS AFTERNOON
AND EARLY EVENING. SURFACE ANALYSIS DEPICTS A THE MAIN FRONTAL
BOUNDARY ACROSS SOUTHWEST WISCONSIN, WITH A LIKELY OUTFLOW
BOUNDARY LAID OUT ACROSS NORTHERN ILLINOIS WHERE ARE STARTING TO
SEE SOME AGITATED/TOWERING CUMULUS IN AN ALREADY MOSTLY UNCAPPED
ENVIRONMENT AHEAD OF BOUNDARY. UPPER FORCING IS STILL SUBTLE,
AND THUS WE ARE NOT LOOKING AT MORE THAN WIDELY SCATTERED
THUNDERSTORMS, HOWEVER, WITH SOMEWHAT SLOW STORM MOTION,
LOCALLY HEAVY RAINFALL WOULD LIKELY OCCUR IN A FEW OF THESE
STORMS. OUR OTHER MECHANISM OF FOCUS WILL BE THE LAKE BREEZE
THIS AFTERNOON. 12Z HREF PAINTS A STRIPE OF 2+ INCH RAINFALL
TOTALS ALONG THE NORTHERN OUTFLOW BOUNDARY ALONG AN AREA FROM
ROCKFORD TO WAUKEGAN, SO WE WILL NEED TO MONITOR THIS AREA.
SEVERE WEATHER WISE, THE MORNING DVN SOUNDING IS MOIST WITH HIGH
FREEZING LEVELS AND WEAK MIDLEVEL LAPSE RATES. THERE IS ENOUGH
FLOW TO SUPPORT SOME BRIEF STORM ORGANIZATION WHICH COULD HAVE
GUSTY OUTFLOW WINDS.
KMD
KMD
DISCUSSION
ISSUED AT 345 AM CDT TUE JUN 24 2025
THROUGH WEDNESDAY:
EARLY THIS MORNING, WE FIND A DECAYING LINE OF SHOWERS
EXTENDING FROM EASTERN IA UP INTO CENTRAL WI. THIS LINE IS
CHURNING ALONG A STATIONARY FRONT TO OUR NORTHWEST AND HAD
RECENTLY FEATURED SEVERAL EMBEDDED THUNDERSTORMS, BUT DIURNAL
COOLING HAD DONE AWAY WITH THOSE. A COUPLE OF OUTFLOW BOUNDARIES
ORIGINATING FROM THIS LINE MADE THEIR WAY ACROSS NORTHERN
PORTIONS OF THE CWA LATE LAST EVENING BRINGING BRIEF PERIODS OF
GUSTY WINDS AND LEAVING SITES SLIGHTLY COOLER IN THEIR WAKE.
THIS LINE SHOULD REMAIN FOCUSED TO OUR NORTHWEST THROUGH THE
MORNING, ALTHOUGH SOME SCATTERED SHOWERS OR STORMS COULD VERY
WELL MAKE IT INTO OUR NORTHWEST DURING THE MORNING, ESPECIALLY
AFTER INSTABILITY BUILDS SOUTHEAST OF THE FRONT AS CONDITIONS
WARM. BUT IT'S UNLIKELY THAT WE'LL SEE ANY ACTIVITY GET INTO THE
CHICAGO METRO PRIOR TO NOON AS PROFILES DRY QUICKLY AS YOU MOVE
AWAY FROM THE FRONT. HOWEVER, DURING THE AFTERNOON AND EVENING,
THE FRONT WILL BEGIN TO PIVOT SOUTH INTO SOUTHERN WI AND DEEP
LAYER MOISTURE WILL POOL OVER NORTHERN IL INCREASING SHOWER AND
STORM CHANCES AROUND THE AREA FOR THE LATTER HALF OF THE DAY.
DESPITE THIS DEEP MOIST ADVECTION, COVERAGE LOOKS LARGELY
ISOLATED TO SCATTERED. IN FACT, PRECIP COVERAGE FOR TODAY HAS
BEEN ON A CONSISTENT DOWNWARD TREND AMONG GUIDANCE.
THE UPPER HIGH IN THE LOWER MIDWEST RESPONSIBLE FOR THE RECENT
HEATWAVE WILL KEEP THE BETTER SHEAR AND FORCING MECHANISMS
SHUNTED WELL TO OUR NORTH. THIS SHOULD HELP INHIBIT ANY
ORGANIZED SEVERE CONVECTION LATER TODAY. HOWEVER, UPWARDS OF A
FEW THOUSAND J/KG OF MLCAPE COULD BUILD OVER THE AREA BY THIS
AFTERNOON WITH ELS ON FORECAST SOUNDINGS AS HIGH AS 15 KM AGL.
ACCORDINGLY, WE MAY SEE A FEW TALLER STORMS QUICKLY GO UP THIS
AFTERNOON, BUT WITH THE LACK OF SHEAR, HOPEFULLY THEY'LL BE JUST
AS QUICK TO DROWN THEMSELVES OUT. ANY DEEPER STORMS MAY PRODUCE
GUSTY TO MARGINALLY DAMAGING WINDS, ESPECIALLY EARLIER IN THE
AFTERNOON WHILE THERE'S STILL A GOOD AMOUNT OF DRY LAYER AIR FOR
ENTRAINMENT. THUNDER CHANCES SHOULD WANE AFTER SUNSET AS
DIURNAL COOLING EATS AWAY AT INSTABILITY, ALTHOUGH ENOUGH WILL
REMAIN WHERE A FEW STORMS OR HEAVIER DOWNPOURS COULD DEVELOP
DURING THE NIGHT.
WE'VE BEEN CLOSELY WATCHING FOR A POTENTIAL FOR LOCALIZED
FLOODING TODAY. WITH A UNIDIRECTIONAL DEEP SHEAR PROFILE
ORIENTED ROUGHLY PARALLEL TO THE FRONT TODAY, THERE ARE CONCERNS
THAT TRAINING CONVECTION COULD ENSUE, MAINLY LATER TODAY AND
TONIGHT AFTER THE DEEP MOISTURE FILLS IN. MODELS AREN'T REALLY
SHOWING THIS SIGNAL EXPLICITLY, BUT A MAJORITY OF THEM CONTINUE
TO PAINT SCATTERED SPLOTCHES OF 1-2" OF QPF AROUND THE CWA
THROUGH WEDNESDAY MORNING. THE SEEMINGLY GREATEST FLOODING
POTENTIAL EXISTS ACROSS OUR NORTH AND NORTHWEST AND WHERE THEY
WILL SPEND MORE TIME IN THE AMPLE ENVIRONMENT NEAR THE FRONT,
BUT THE FLOODING THREAT IN GENERAL APPEARS RATHER LOW AND
LOCALIZED AT THIS TIME.
THE LOW LEVELS WILL BE NEARLY SATURATED TONIGHT INTO WEDNESDAY,
WHICH WILL PROMOTE LOW-HANGING STRATUS AND POSSIBLY SOME MINOR
FOG THROUGH WEDNESDAY MORNING. SCATTERED SHOWERS ARE LOOKING
PRETTY LIKELY WEDNESDAY MORNING, BUT THE ACTIVITY SHOULD WANE
THROUGH THE DAY AS THE SURFACE FRONT AND DEEP MOISTURE RETREAT
BACK TO OUR NORTH.
ON THE TOPIC OF TEMPERATURE, IT SHOULD BE ANOTHER HOT SUMMER
DAY OUT THERE TODAY, ALTHOUGH NOT QUITE AS OPPRESSIVE AS WE'VE
SEEN IN RECENT DAYS, ESPECIALLY ACROSS OUR NORTH. THERE IS A BIT
MORE SPREAD IN TEMPERATURE GUIDANCE FOR TODAY THAN WE'D LIKE TO
SEE, MAINLY IN OUR NORTH, BUT THAT'S BECAUSE IT'S BEING
INFLUENCED BY THE POTENTIAL SCATTERED CONVECTION. OUR NORTH AND
NORTHWEST CWA LOOK TO BE THE "COOLEST" TODAY WITH HIGHS FORECAST
IN THE MIDDLE AND UPPER 80S WHILE LOWER 90S ARE EXPECTED NEAR
AND SOUTH OF I-80. AFTERNOON HEAT INDICES LOOK TO RANGE FROM THE
LOWER 90S IN OUR NORTH TO AROUND 100 NEAR AND SOUTH OF I-80. NO
CHANGES WERE MADE TO THE HEAT ADVISORY ISSUED YESTERDAY FOR
COUNTIES SOUTH OF I-80 FOR THE CUMULATIVE EFFECTS OF NOW FOUR
CONSECUTIVE DAYS OF HEAT INDICES NEAR OR ABOVE 100 DEGREES.
HIGHS ON WEDNESDAY LOOK SLIGHTLY COOLER IN THE 80S TO AROUND 90
WITH PEAK HEAT INDICES IN THE UPPER 90S AND APPROACHING 100 IN
OUR SOUTH. ONSHORE FLOW AROUND THE LAKE DURING THE DAY WILL KEEP
CONDITIONS THERE SEVERAL DEGREES COOLER WITH LOWER AND MIDDLE
70S EXPECTED ALONG THE SHORELINE DURING THE AFTERNOON.
DOOM
WEDNESDAY NIGHT THROUGH MONDAY:
THE UPPER LEVEL RIDGE IS PROGGED TO FLATTEN THROUGH MID-WEEK,
AND EVENTUALLY SHIFT EASTWARD THIS WEEKEND. 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 SETTLES 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 THE
AFTERNOON/EVENING PEAKS OF DIURNAL HEATING AND INSTABILITY.
MODELS OFTEN DON'T DO WELL WITH TIMING OF THESE SHORTER
AMPLITUDE WAVES (OR MCVS GENERATED BY UPSTREAM CONVECTION)
FARTHER OUT IN TIME, SO CONFIDENCE IS SOMEWHAT LOW IN TIMING
PERIODS OF HIGHER POPS.
AS INDICATED IN THE PREVIOUS DISCUSSION, 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 APPROACHING 2"
AT TIMES 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.
RATZER
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.
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.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page