660
FXUS63 KLOT 042330
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
630 PM CDT WED JUN 4 2025
KEY MESSAGES
- STEADY RAINFALL TO PERSIST THROUGH TONIGHT IN AREAS NEAR AND
SOUTHEAST OF INTERSTATE 55. ISOLATED THUNDERSTORMS WILL REMAIN
POSSIBLE NEAR AND SOUTH OF THE KANKAKEE RIVER VALLEY DURING
THIS TIME.
DISCUSSION
ISSUED AT 330 PM CDT WED JUN 4 2025
THROUGH THURSDAY NIGHT:
MUCH OF OUR FORECAST AREA HAS BEEN BLANKETED BY RAIN, STRATUS, AND
HAZE/LIGHT FOG THROUGHOUT THE DAY TODAY WITH TEMPERATURES STUCK IN
THE 60S ON THE COOL SIDE OF A SLOW-MOVING COLD FRONT THAT HAS SLOWLY
BEEN SAGGING SOUTHWARD ACROSS THE AREA (QUINTESSENTIAL JUNE WEATHER,
RIGHT?). THE RAIN AND STRATUS HAVE HINDERED DESTABILIZATION EFFORTS
IN OUR SOUTHEASTERN COUNTIES, WHICH THE COLD FRONT STILL HASN'T
FULLY PASSED THROUGH AT PRESS TIME. DON'T REALLY EXPECT THINGS TO
CHANGE MUCH THERE OVER THE NEXT FEW HOURS, BUT MID-LEVEL LAPSE RATES
STILL LOOK TO REMAIN STEEP ENOUGH TO SUPPORT A THREAT FOR ISOLATED
EMBEDDED THUNDERSTORMS WITHIN THE BROADER RAIN SHIELD THAT SHOULD
PERSIST ACROSS OUR SOUTHEASTERN CWA THE REMAINDER OF THIS AFTERNOON
AND INTO TONIGHT. PRECIPITABLE WATER VALUES APPROACHING 2" WILL
CONTINUE TO SUPPORT SOAKING RAINFALL ALONG AND JUST BEHIND THE
FRONT, AND LOCALIZED RAINFALL TOTALS IN EXCESS OF 2" COULD END
UP BEING OBSERVED WHEN ALL IS SAID AND DONE. HOWEVER, THE
ANTECEDENT DRYNESS PRIOR TO THIS RAINFALL AND THE PROLONGED
DURATION OF THIS RAINFALL SHOULD LARGELY PRECLUDE ANY NOTABLE
HYDROLOGIC CONCERNS FROM MATERIALIZING.
SURFACE HIGH PRESSURE CENTERED TO OUR NORTH WILL ALLOW FOR
WINDS TO BECOME LIGHT TONIGHT. WITH SKIES ALSO EXPECTED TO CLEAR
OUT A GOOD BIT IN OUR NORTHERN CWA, SOME FOG DEVELOPMENT MAY
OCCUR. FORECAST GUIDANCE IS ACTUALLY MOST BULLISH ON THIS
OCCURRING OUT OVER LAKE MICHIGAN, AND WITH SURFACE WINDS
EXPECTED TO BE OUT OF THE NORTH, WE'LL NEED TO KEEP AN EYE ON
THIS FOG POTENTIALLY BLEEDING INLAND IF IT DOES END UP
DEVELOPING OVER THE LAKE. OTHERWISE, LOW TEMPERATURES TONIGHT
ACROSS OUR FORECAST AREA SHOULD RANGE FROM THE LOW 50S TO LOW
60S.
DURING THE DAYTIME TOMORROW, THE FRONT WILL HAVE STALLED SOUTH
OF OUR FORECAST AREA, THOUGH THERE IS STILL SOME SPREAD IN
MODEL GUIDANCE REGARDING PRECISELY WHERE THE FRONT WILL SET UP
SHOP. MOST GUIDANCE FAVORS THIS FRONT STALLING COMFORTABLY SOUTH
OF OUR FORECAST AREA, BUT A COUPLE OF MODELS HAVE IT STALLING
CLOSE ENOUGH TO OUR SOUTHERN CWA BORDER TO WHERE SOME SHOWERS
AND MAYBE A THUNDERSTORM COULD STILL AFFECT OUR FAR
SOUTHEASTERN COUNTIES WELL AFTER DAYBREAK. HAVE MAINTAINED SOME
LOWER END POPS (UNDER 30%) NEAR AND SOUTH OF THE KANKAKEE RIVER
VALLEY TO ACCOUNT FOR THIS POSSIBILITY.
PARTLY CLOUDY SKIES ARE OTHERWISE EXPECTED ACROSS THE REMAINDER
OF OUR FORECAST AREA TOMORROW, THOUGH LINGERING CANADIAN
WILDFIRE SMOKE MAY CONTINUE TO RESULT IN HAZY SKIES. IT ALSO
APPEARS THAT A GREATER CONCENTRATION OF THIS SMOKE MAY BE
PRESENT AT GROUND LEVEL COMPARED TO PRIOR DAYS, WHICH HAS
WARRANTED THE ISSUANCE OF AN AIR QUALITY ALERT, PER THE REQUESTS
OF THE ILLINOIS ENVIRONMENTAL PROTECTION AGENCY AND THE INDIANA
DEPARTMENT OF ENVIRONMENTAL MANAGEMENT. DAYTIME TEMPERATURES
TOMORROW SHOULD BE WARMER THAN TODAY'S IN MOST LOCATIONS WITH
HIGHS EXPECTED TO END UP IN THE 70S ACROSS MOST OF OUR FORECAST
AREA. BREEZY ONSHORE FLOW, HOWEVER, WILL KEEP LOCATIONS WITHIN A
FEW MILES OF LAKE MICHIGAN MIRED IN THE UPPER 50S OR 60S FOR
ANOTHER DAY.
OGOREK
FRIDAY THROUGH WEDNESDAY:
PERIODIC SHOWER AND THUNDERSTORM CHANCES WILL CONTINUE FOR
PORTIONS OF THE AREA THROUGH THE END OF THE WEEK AS MULTIPLE
DISTURBANCES MOVE WITHIN THE BROADER QUASI-ZONAL FLOW.
THE FIRST OF THESE WAVES IS EXPECTED TO MOVE ACROSS THE MID-
MISSISSIPPI AND OHIO VALLEYS ON FRIDAY. THERE CONTINUE TO BE
DIFFERENCES IN POSITION AND TRACK OF THE WAVE AMONG THE GLOBAL
GUIDANCE, WITH GFS REMAINING FURTHEST NORTH AND BRINGING SHOWERS
INTO SOUTHERN PORTIONS OF THE AREA, WHEREAS THE ECMWF IS WELL
SOUTH OF THE AREA LEADING TO DRY CONDITIONS AREAWIDE. TEND TO
FAVOR THE ECMWF AT THIS RANGE AND HAVE CAPPED SHOWER CHANCES IN
THE 20-40% RANGE (HIGHEST WELL SOUTH OF I-80). SUSPECT FURTHER
REDUCTIONS WILL BE WARRANTED WITH LATER UPDATES.
A SUBSEQUENT WAVE ARRIVES ON SATURDAY WHICH COULD LEAD TO
ADDITIONAL MAINLY ISOLATED SHOWER DEVELOPMENT (~20% CHANCE).
SURFACE HIGH PRESSURE CENTERED OVER THE UP OF MICHIGAN SHOULD
HELP HOLD THIS ACTIVITY TO AREAS MAINLY WEST AND SOUTH OF THE
CHICAGO METRO BUT A STRAY SHOWER CAN'T BE RULED OUT AMIDST
OTHERWISE DRY AND SEASONABLE CONDITIONS.
AN UPPER LOW IS THEN FORECAST TO DEVELOP ACROSS CANADA OVER THE
WEEKEND AND DESCEND TOWARD THE GREAT LAKES REGION EARLY NEXT
WEEK. A COLD FRONT EXTENDING WELL SOUTH OF AN ASSOCIATED SURFACE
LOW IN WESTERN ONTARIO WILL MOVE THROUGH THE AREA ON SUNDAY
LEADING TO SCATTERED THUNDERSTORM CHANCES. DEPENDING ON THE
TIMING OF THE FRONTAL PASSAGE WE WILL HAVE TO KEEP AN EYE ON THE
POTENTIAL FOR SEVERE WEATHER SUNDAY AFTERNOON INTO EARLY
EVENING. AS EMBEDDED WAVES/VORT LOBES ROUND THE CLOSED MID-
UPPER LOW ADDITIONAL SHOWER AND STORM CHANCES MAY CONTINUE ON
MONDAY.
TEMPERATURES WILL REMAIN NEAR SEASONABLE THROUGH THE PERIOD
WITH HIGHS MAINLY IN THE MID-UPPER 70S INLAND FROM THE
LAKESHORE.
PETR
AVIATION /00Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 630 PM CDT WED JUN 4 2025
AVIATION FORECAST CONCERNS FOR 00Z TAFS:
- SHRA LINGERS THIS EVENING FOR KMDW/KGYY, WITH OCNL MVFR FOR
KMDW AND IFR/LIFR LIKELY FOR KGYY.
- LOW STRATUS/FOG OFF OF LAKE MICHIGAN POSSIBLE LATER TONIGHT,
MAY AFFECT KORD/KMDW THOUGH LOW CONFIDENCE.
- NEAR-SURFACE WILDFIRE SMOKE COULD IMPACT VISIBILITY SOMEWHAT
INTO THURSDAY.
NEARLY STATIONARY COLD FRONT SITS FROM NEAR KSTL TO JUST SOUTH
OF KLAF EARLY THIS EVENING. RA/SHRA WILL PERSIST ALONG/NORTH OF
THE FRONT THIS EVENING AS A MID-LEVEL DISTURBANCE TRACKS
NORTHEAST ALONG THE FRONTAL ZONE, MAINLY IMPACTING KGYY WITH
IFR/LIFR CONDITIONS IN -RA AND KMDW WITH OCCASIONAL -SHRA AND
PATCHY MVFR CONDITIONS. RAIN SHOULD EVENTUALLY SHIFT SLOWLY AWAY
TO THE SOUTHEAST OVERNIGHT. SIGNAL EVIDENT IN MODEL GUIDANCE
SUGGESTS THAT SOME FOG/LOW STRATUS MAY DEVELOP ACROSS LAKE
MICHIGAN LATER THIS EVENING/OVERNIGHT, AND MAY TRY TO SPREAD
ACROSS THE CHICAGO METRO TERMINALS ON NORTHEAST LOW-LEVEL WINDS.
CONFIDENCE IS FAIRLY LOW IN HOW FAR INLAND THIS WILL SPREAD,
BUT DID INCLUDE A TEMPO FOR MVFR CONDITIONS PREDAWN FOR
KORD/KMDW. KGYY, CLOSER TO THE LAKE, IS MORE LIKELY TO SEE AT
LEAST PREVALENT MVFR CONDITIONS INTO MID-THURSDAY MORNING. WILL
NEED TO MONITOR STRATUS/FOG TRENDS FOR THESE LOCATIONS LATER
TONIGHT.
OTHERWISE, HIGH-RES HRRR CONTINUES TO DEPICT INCREASED NEAR-
SURFACE SMOKE CONCENTRATIONS AS EARLY AS LATER THIS EVENING FOR
KRFD AND TOMORROW FOR THE CHICAGO TERMINALS. THESE CONCENTRATION
FORECASTS DON'T ALWAYS DIRECTLY TRANSLATE TO VISIBILITY IMPACTS,
THOUGH IT APPEARS PRUDENT TO MAINTAIN SOME MINOR VIS IMPACT IN
THE TAFS. NORTHEAST WINDS ARE EXPECTED THROUGH THE PERIOD,
AROUND 10 KT TONIGHT AND 10-15 KT THURSDAY ESPECIALLY NEAR LAKE
MICHIGAN.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...AIR QUALITY ALERT UNTIL MIDNIGHT CDT THURSDAY NIGHT FOR ILZ005-
ILZ006-ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-
ILZ106-ILZ107-ILZ108.
IN...AIR QUALITY ALERT FROM MIDNIGHT TONIGHT TO MIDNIGHT CDT
THURSDAY NIGHT FOR INZ001-INZ002-INZ010-INZ011.
LM...NONE.
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