424
FXUS63 KLOT 240550
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1250 AM CDT TUE JUN 24 2025
KEY MESSAGES
- HEAT INDICES WILL STILL BE IN THE UPPER 90S TO NEAR 100
THROUGH MUCH OF THE WEEK. THE CURRENT HEAT ADVISORY WAS
EXTENDED INTO TUESDAY FOR SELECT COUNTIES SOUTH OF INTERSTATE
80.
- PERIODIC SHOWER AND STORM CHANCES EXIST THROUGH THIS WEEK.
SOME MAY BE SEVERE WITH DAMAGING WINDS AND FLASH FLOODING.
DISCUSSION
ISSUED AT 252 PM CDT MON JUN 23 2025
THROUGH TUESDAY:
RECENT WATER VAPOR SATELLITE IMAGERY IS SHOWING A NARROW
CORRIDOR OF HIGHER MOISTURE FROM LINCOLN, NE THROUGH MARQUETTE
MICHIGAN. SWITCHING OVER TO VISIBLE OR IR IMAGERY, TALLER STORMS
ARE FIRING ALONG A COLD FRONT FROM NORTHERN IOWA TO CENTRAL
WISCONSIN. RECENT MESOANALYSIS SHOWS A STRONG SURFACE
TEMPERATURE AND ML CAPE GRADIENT CO-LOCATED WITH THIS BOUNDARY.
HIGH-RES MODELS ARE SUGGESTING THAT THIS FRONT WILL GRADUALLY
SLINK ITS WAY THROUGH IOWA AND WISCONSIN AND EVENTUALLY MOVE
INTO OUR NORTH AND NORTHWEST CWA SOMETIME TUESDAY MORNING. BUT
BY THE TIME IT GETS TO THE FORECAST AREA, MODELS ARE SUGGESTING
IT STALLS OUT IN ITS MOVEMENT. THE HIGHEST CHANCE FOR STORMS
AHEAD OF THE FRONT WOULD BE NORTH AND WEST OF THE FOX VALLEY,
THOUGH MUCH OF THE AREA WILL REMAIN DRY. ONE THING THAT WILL BE
CLOSELY MONITORED THROUGH THE NIGHT IS ANY OUTFLOW THAT DEVELOPS
FROM THE STORMS TO THE NORTHWEST THAT COMES DOWN ACROSS OUR
AREA. THIS OUTFLOW COULD TRIGGER NEW STORMS THAT COULD DEVELOP
OVER THE AREA TONIGHT, BUT THERE IS LOWER CONFIDENCE IN THE
EXACT TIMING AND LOCATION THAT THEY DEVELOP.
TEMPERATURES REMAIN IN THE MID 90S AREA WIDE AND THE DEW POINTS
HAVN'T MIXED OUT MUCH TODAY AND REMAIN IN THE LOWER 70S
RESULTING IN HEAT INDEX VALUES IN THE LOW 100S. FOR A THIRD
STRAIGHT DAY, HOT AND HUMID CONDITIONS SURROUND THE FORECAST
AREA. AND TEMPERATURES ARE ONLY GOING TO DIMINISH TONIGHT
GRADUALLY AND COULD STILL BE ABOVE 80 JUST BEFORE MIDNIGHT.
TEMPERATURES WILL ONCE AGAIN BE WARM TOMORROW. LUCKILY, THE
PREVIOUSLY MENTIONED FRONT SHOULD SLOWLY DROP SOUTH THROUGH THE
DAY WHICH SHOULD HELP MITIGATE EXTREME TEMPERATURES FOR AREAS
NORTH OF INTERSTATE 80 TOMORROW. HOWEVER, FOR LIVINGSTON,
KANKAKEE, FORD, IROQUOIS COUNTIES IN ILLINOIS AND BENTON, NEWTON
AND JASPER IN INDIANA, THE COMBINATION OF WARM TEMPERATURES AND
HIGH SURFACE DEW POINTS OUT AHEAD OF THE FRONT AND HAVE A
CHANCE FOR HEAT INDICES ABOVE 100 ONCE AGAIN FOR A FOURTH
STRAIGHT DAY. GIVEN THAT HEAT IMPACTS COMPOUND OVER TIME, THE
HEAT ADVISORY FOR THOSE COUNTIES WAS EXTENDED THROUGH TOMORROW
AFTERNOON DURING PEAK HEATING.
AS THAT FRONT MOVES SOUTH TOMORROW, THERE WILL BE A RENEWED
EFFORT FOR SHOWERS AND STORMS ACROSS THE AREA. FORCING ALONG THE
GRADIENT STILL LOOKS FAIRLY MARGINAL, AS DOES THE SHEAR.
COVERAGE IS LOOKING WIDELY SCATTERED ALONG AND AHEAD OF THE
FRONT AS IT MOVES SOUTH. THE FORECAST AREA REMAINS IN A LEVEL 1
OUT OF 5 THREAT FOR SEVERE WEATHER FROM THE STORM PREDICTION
CENTER, WITH THE MAIN SEVERE THREAT BEING FROM DAMAGING WIND.
HOWEVER, PRECIPITABLE WATER LEVELS WILL REMAIN HIGH. RECENT CAMS
ARE SHOWING NEAR IF NOT RECORD P-WATS FOR THIS TIME OF YEAR
COMPARED TO HISTORICAL KDVN SOUNDINGS. WITH THIS TYPE OF SET-UP,
IT WOULD NOT BE SURPRISING IF MOST OF THE STORMS HAD A NICE
STEADY RAIN RATE THAT THE SOIL CAN HANDLE. BUT WITH P-WATS AS
HIGH AS THESE, ISOLATED DOWNPOURS WITH RAIN RATES OF 1-3 INCHES
PER HOUR ARE POSSIBLE. THAT'S NOT TO SAY THAT THEY WILL BE
RAINING FOR THE FULL HOUR AT THAT RATE, BUT ENOUGH TO KEEP THE
CONCERN FOR LOCALIZED FLOODING IN THE FORECAST.
DK
WEDNESDAY 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 /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 1250 AM CDT TUE JUN 24 2025
KEY MESSAGES:
- GUSTY NORTHWEST TO NORTH WIND SHIFT MOVING ACROSS THE CHICAGO
METRO AT THE START OF THE TAF.
- LAKE BREEZE TO TURN WINDS EAST TO NORTHEAST THIS AFTERNOON.
- ISOLATED TO SCATTERED SHOWERS/STORMS POSSIBLE THIS AFTERNOON.
A LONG LIVED OUTFLOW BOUNDARY CONTINUES TO PROGRESS ACROSS THE
CHICAGO METRO EARLY THIS MORNING. THIS RESULTED IN A BRIEF
PERIOD OF GUSTS IN EXCESS OF 20KT OUT OF THE NORTHWEST AT ORD
AND SUSPECT THIS WILL CONTINUE THROUGH MDW AND POTENTIALLY GYY.
WINDS THEN EASE AND TURN LIGHT AND VARIABLE THE REMAINDER OF THE
OVERNIGHT HOURS. A STRAY SHOWER CAN'T BE RULED OUT IN THE WAKE
OF THIS OUTFLOW BOUNDARY, BUT SO FAR THEY HAVE STRUGGLED TO HOLD
TOGETHER.
WINDS SETTLE BACK INTO A WEST TO SOUTHWEST DIRECTION AFTER
DAYBREAK. CONVECTION CURRENTLY ACROSS NORTHWEST MO AND
SOUTHWEST IA IS FORECAST TO GRADUALLY MOVE TOWARD THE AREA
THROUGH OVERNIGHT THROUGH THE MORNING HOURS. THIS MAY ATTEMPT TO
FORM INTO A WEAK MCV WHICH COULD AID IN STORM DEVELOPMENT HERE
LOCALLY BY THIS AFTERNOON AS IT MOVES FROM WEST TO EAST ACROSS
THE AREA. THUS HAVE OPTED TO MAINTAIN PROB30 GROUPS FOR TSRA TO
ACCOUNT FOR THIS POTENTIAL. VARIABLE GUSTY WINDS MAY ACCOMPANY
ANY OF THESE STORMS IN ADDITION TO HEAVY DOWNPOURS LEADING TO
REDUCED VISIBILITY.
MEANWHILE A LAKE BREEZE IS ALSO PROGGED TO PUSH INLAND DURING
THE EARLY TO MID AFTERNOON TIMEFRAME TURNING WINDS EAST TO
NORTHEASTERLY. THIS BOUNDARY COULD ALSO SERVE AS ANOTHER
MECHANISM FOR LIFT FOR ADDITIONAL THUNDERSTORM DEVELOPMENT IF
THE AFOREMENTIONED MCV RELATED STORMS DON'T MATERIALIZE.
IN THE WAKE OF THE AFTERNOON/EARLY EVENING SHOWERS AND STORMS,
MVFR CEILINGS MAY DEVELOP TONIGHT INTO EARLY WEDNESDAY MORNING.
FOR NOW HAVE INTRODUCED A LOWER-END VFR CIG AND A SCATTERED MVFR
MENTION DUE TO LOWER CONFIDENCE AT THIS RANGE.
PETR
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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