295
FXUS63 KLOT 302352
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
652 PM CDT WED JUL 30 2025
KEY MESSAGES
- PERIODS OF RAIN ARE EXPECTED THIS EVENING AND OVERNIGHT AS A
SLOW-MOVING WEATHER SYSTEM MOVES OVERHEAD, SOME WITH LOCALLY
TORRENTIAL RAINFALL. FLOOD WATCH REMAINS IN EFFECT FOR AREAS
NEAR AND SOUTH OF I-80 THROUGH TONIGHT.
- HIGH WAVES AND RIP CURRENTS WILL LEAD TO A HIGH SWIM RISKS AT
ALL LAKE MICHIGAN BEACHES THROUGH AT LEAST FRIDAY AFTERNOON.
- COOLER TEMPERATURES AND MORE COMFORTABLE HUMIDITY LEVELS WILL
ARRIVE TOMORROW AND LAST THROUGH THE WEEKEND.
UPDATE
ISSUED AT 652 PM CDT WED JUL 30 2025
EARLIER WAVE OF HEAVY RAIN-PRODUCING SHOWERS AND THUNDERSTORMS
HAS MOVED EAST OF THE REGION. CURRENTLY, IN A BIT OF A LOCAL
ACTIVITY MINIMA, BUT WE'RE KEEPING A CLOSE EYE ON A FEW FEATURES.
AT THE SURFACE, A COMPOSITE OUTFLOW BOUNDARY/COLD FRONT LOOKS LIKE
IT'S SLIPPED SOUTH OF ABOUT THE I-80 CORRIDOR, WITH BREEZY NORTH
TO NORTHEASTERLY WINDS IN ITS WAKE. THIS FRONTAL ZONE SEEMS
LIKE IT CONNECTS UP TO PERHAPS A DIFFUSE AND LOCALIZED SURFACE
LOW IN THE VICINITY OF GALESBURG/PEORIA EMBEDDED WITHIN A
BROADER INVERTED TROUGH AXIS. WHILE THE AFOREMENTIONED FRONTS
SOUTHWARD PROGRESSION AND EARLIER CONVECTION HAVE BOTH WORKED TO
DIMINISH OVERALL INSTABILITY, IT'S CERTAINLY NOT GONE ENTIRELY.
LATEST RAP/SPC MESOANALYSIS DEPICTS A FEW HUNDRED J/KG OF
MLCAPE NEAR AND SOUTH OF THE FRONTAL ZONE, WITH NEARLY 1000 J/KG
OF MUCAPE ANALYZED ACROSS SOUTHERN LA SALLE-LIVINGSTON-FORD
COUNTIES.
IN THIS VICINITY ACROSS THE SOUTHWEST QUARTER OF OUR FORECAST AREA,
VWPS, SURFACE OBSERVATIONS, AND LATEST RAP GUIDANCE INDICATE
STRONG VEERING OF THE LOW-MID LEVEL WIND FIELD, FROM EASTERLY
AT THE SURFACE TO WESTERLY AT 700-500 MB, INDICATIVE OF
PERSISTENT, BROAD WARM ADVECTION. ADDITIONALLY, A MODEST
SOUTHWESTERLY 700 MB JET ENHANCEMENT IS ALSO EVIDENT IN RECENT
MODEL ANALYSES, WHICH ESSENTIALLY IMPINGES UPON THE PREVIOUSLY-
MENTIONED SURFACE FRONTAL BOUNDARY. WITH PWATS STILL NORTH OF 2
INCHES IN THIS AREA, THERE'S SOME CONCERN THAT ADDITIONAL
SHOWERS WITH TORRENTIAL RAINFALL MAY CONTINUE TO DEVELOP THIS
EVENING AS DIVERGENCE WITHIN THE RIGHT ENTRANCE REGION OF A
QUASI-ZONAL JET STREAK ACROSS NORTHERN WI/MI SLOWLY INTENSIFIES.
CLOUD-BEARING FLOW IS EXCEPTIONALLY SLOW ACROSS PARTS OF OUR
AREA, WHERE SURFACE EASTERLIES BECOME WESTERLY IN THE MID
LEVELS, YIELDING NEARLY STATIONARY CELL MOTIONS. NEARLY MOIST
ADIABATIC PROFILES WILL PROBABLY YIELD LITTLE IN THE WAY OF
ADDITIONAL LIGHTNING ACTIVITY, BUT DEEP WARM CLOUD DEPTHS
(NEARLY 15 KFT) WILL FACILITATE CLASSIC LOW ECHO CENTROID
SHOWERS WITH DECEPTIVELY HIGH RAIN RATES. HAVE ALREADY SEEN THIS
WITH ONGOING SHOWERS ACROSS PARTS OF BUREAU COUNTY WHERE
30-MINUTE RAINFALL RATES HAVE LOCALLY EXCEEDED 1.5 INCHES.
RECENT HRRR RUNS APPEAR TO HAVE CAUGHT ONTO THINGS FAIRLY WELL,
AND CONSISTENTLY DEPICT AN AXIS OF HEAVY RAINFALL DEVELOPING
ACROSS PARTS OF LA SALLE, LIVINGSTON, AND FORD COUNTIES THIS
EVENING. GIVEN EVERYTHING MENTIONED ABOVE, DID NOT FEEL
COMFORTABLE LETTING THE INHERITED FLOOD WATCH GO AT 7 PM, SO
DID EXTEND THIS THROUGH LATE TONIGHT AND EXPANDED IT WESTWARD.
GREATEST CONCERN THROUGH MID-EVENING IS ACROSS THAT LA SALLE TO
FORD COUNTY AXIS, BUT ADDITIONAL EMBEDDED HEAVY SHOWERS MAY
BLOSSOM EASTWARD LATE THIS EVENING AND OVERNIGHT. HAVE ALSO KEPT
THE I-80 CORRIDOR COUNTIES IN THIS EXTENDED WATCH FOR THIS
REASON. CAN'T ENTIRELY RULE OUT HAVING TO MAKE ANOTHER NORTHWARD
EXPANSION TO THE WATCH, BUT AT THIS TIME, IT SEEMS LIKE THE
EFFECTIVE BOUNDARIES MAY SAG FAR ENOUGH SOUTH TO KEEP THE MAIN
THREAT FOR ADDITIONAL HEAVY RAIN SOUTH OF CHICAGO.
CARLAW
DISCUSSION
ISSUED AT 226 PM CDT WED JUL 30 2025
THROUGH THURSDAY:
RECENT RADAR IMAGERY DEPICTS SHOWERS AND STORMS MOVING EASTWARD
ACROSS THE AREA AT PRESS TIME AHEAD OF AN MCV/SHORTWAVE MOVING
EASTWARD ACROSS THE MISSISSIPPI RIVER. MEANWHILE, A SECOND AREA
OF SHOWERS AND EMBEDDED THUNDERSTORMS STRETCHES FROM FAR
NORTHERN IOWA EASTWARD THROUGH MUCH OF SOUTHERN WISCONSIN ALONG
THE NORTHERN FLANK OF THE MCV AND ALONG A BROAD FRONTAL ZONE
DRIFTING SOUTHWARD THROUGH THE GREAT LAKES. BETWEEN BOTH
FEATURES, RELATIVELY TRANQUIL CONDITIONS RESIDE WITH BROKEN
CLOUD COVER AND TEMPERATURES IN THE MID 70S.
OVER THE COMING HOURS, THE EXPECTATION IS FOR THE MAIN AXIS OF
SHOWERS AND STORMS TO SHIFT EASTWARD OUT OF OUR AREA ONLY TO BE
REPLACED BY THE SECONDARY AREA OF SHOWERS AND EMBEDDED STORMS
DROPPING SOUTHWARD OUT OF WISCONSIN. A BROAD AREA OF UPPER-
LEVEL DIFFLUENCE IN THE RIGHT ENTRANCE REGION OF A PASSING JET
STREAK IN TANDEM WITH PWATS NEAR 2" SHOULD AFFORD SURPRISINGLY
EFFICIENT RAIN RATES THIS EVENING PARTICULARLY WHERE POCKETS OF
INSTABILITY STILL RESIDE. WITH THAT SAID, THE SIGNAL FOR
WIDESPREAD, TORRENTIAL RAINFALL TONIGHT IS MUCH LOWER THAN IT
HAD LOOKED 12 HOURS AGO (LIKELY AS A RESULT TO A DIFFERENT
EVOLUTION OF CONVECTION TODAY THAN PERHAPS EXPECTED). AS A
RESULT, WILL GO AHEAD AND TRIM THE FLOOD WATCH WHERE RAIN HAS
ALREADY PASSED AND LET THE EVENING SHIFT REMOVE THE REST LATER
TODAY. NOTE THERE MAY STILL BE A VERY LOW-END THREAT ON A VERY
LOCALIZED BASIS (CALL IT A 5% CHANCE FOR FLOODING AT ANY GIVEN
LOCATION). MEANWHILE, INCREASING NORTH TO NORTHEASTERLY FLOW OFF
THE LAKE WILL LEAD TO BUILDING WAVES ON LAKE MICHIGAN,
RESULTING IN A HIGH SWIM RISK THIS EVENING ONWARD AT ALL LAKE
MICHIGAN BEACHES.
TOMORROW, THE BACK EDGE OF THE SHORTWAVE WILL SHIFT EASTWARD
CAUSING SHOWERS TO TAPER FROM NORTHEAST TO SOUTHEAST. SHOWERS OR
SPRINKLES MAY LAST THE LONGEST AT LAKESHORE LOCATIONS WHERE
ONSHORE FLOW AND TUMBLING 850MB TEMPERATURES MAY AFFORD MODEST
LAKE INSTABILITY BEFORE DRY AIR RUSHES INTO THE REGION. OUTSIDE
TAPERING RAIN CHANCES, TOMORROW WILL FEEL QUITE DIFFERENT
COMPARED TO THE PAST WEEK WITH HIGHS ONLY IN THE LOW TO MID 70S
AND MUCH LOWER HUMIDITY LEVELS. CONTINUED NORTH TO NORTHEASTERLY
ONSHORE WINDS WILL MAINTAIN A HIGH SWIM RISK AT ALL LAKE
MICHIGAN BEACHES. FINALLY, HAVE INTRODUCED NEAR-SURFACE SMOKE TO
THE FORECAST OWING TO UPSTREAM OBSERVATIONS OF 2-5 MILE
VISIBILITIES ACROSS THE UPPER GREAT LAKES (THAT AIRMASS WILL
COME OUR WAY BEHIND THE FRONT TOMORROW).
BORCHARDT
THURSDAY NIGHT THROUGH WEDNESDAY:
SURFACE HIGH PRESSURE WILL REMAIN STATIONED OVER THE GREAT
LAKES FRIDAY THROUGH THE WEEKEND. ABUNDANT SUNSHINE CAN THUS BE
EXPECTED ACROSS THE REGION, THOUGH IT'S POSSIBLE THAT LINGERING
WILDFIRE SMOKE ALOFT COULD CONTINUE TO GIVE THE SKY A MILKY LOOK
AT TIMES. ANTICYCLONIC FLOW AROUND THE SURFACE HIGH WILL
REINFORCE THE COOLER AND DRIER AIR MASS OVER THE REGION, LEADING
TO CONTINUED BELOW TO NEAR-NORMAL TEMPERATURES (HIGHS IN THE
70S TO LOW-MID 80S AND LOWS IN 50S TO MID 60S) AND COMFORTABLE
HUMIDITY LEVELS. SYNOPTIC CONDITIONS FAVOR LITTLE TO NO
PRECIPITATION IN OUR AREA THROUGH THE WEEKEND. HOWEVER, THE
UNSEASONABLY COOL LOW-LEVEL AIR (850 MB TEMPERATURES IN THE
BOTTOM 10% OF REGIONAL SOUNDING CLIMATOLOGY) SPREADING OVER A
MILD LAKE MICHIGAN WITH WATER TEMPERATURES STILL IN THE 70S
COULD SUPPORT A CONDITIONAL POTENTIAL FOR ISOLATED LAKE-INDUCED
SHOWERS OR DRIZZLE THURSDAY NIGHT INTO FRIDAY, PENDING THE
PRESENCE OF SUFFICIENT LOW-LEVEL MOISTURE AND THE DEVELOPMENT OF
ANY LOW-LEVEL CONVERGENCE ZONES. BOOSTED POPS A BIT FOR THIS
TIME FRAME TO ACCOUNT FOR THIS POSSIBILITY, BUT HAVE MAINTAINED
A DRY FORECAST FOR NOW GIVEN THE LINGERING UNCERTAINTIES AND
ONLY MARGINAL LAKE EFFECT PARAMETERS IN PLAY.
MEDIUM RANGE GUIDANCE CONTINUES TO INDICATE THAT THE GREAT
LAKES SURFACE HIGH WILL DEPART GOING INTO EARLY NEXT WEEK,
OPENING THE DOOR FOR WARMER AND MORE HUMID CONDITIONS TO RETURN,
ALONG WITH OUR NEXT CHANCES FOR PRECIPITATION AS UPPER-LEVEL
SHORTWAVE DISTURBANCES START TO GET FUNNELED BACK INTO THE
REGION. HOWEVER, THERE IS STILL A FAIR AMOUNT OF SPREAD AMONGST
THE LATEST ENSEMBLE OUTPUT REGARDING HOW QUICKLY THIS WILL
OCCUR AND JUST HOW WARM IT MIGHT GET NEXT WEEK, ALONG WITH THE
TIMING OF ANY POTENTIAL SHOWERS OR STORMS NEXT WEEK. THIS
SPREAD APPEARS TO BE TIED TO THE STRENGTH AND TRAJECTORY OF A
REINFORCING UPPER-LEVEL TROUGH DIVING INTO THE GREAT LAKES
AND/OR NORTHEASTERN CONUS FROM CANADA, WHICH WILL INFLUENCE THE
EXTENT TO WHICH AN UPPER-LEVEL RIDGE OVER THE SOUTHWESTERN
CONUS IS IMPEDED AS IT ATTEMPTS TO SLIDE EASTWARD. REGARDLESS,
THE OVERALL TREND SHOULD STILL BE TOWARDS WARMER AND MORE HUMID
CONDITIONS NEXT WEEK, AND THIS TREND IS REFLECTED IN THE LATEST
NBM OUTPUT. THE NBM'S POPS, HOWEVER, ARE LIKELY TOO BROAD-
BRUSHED AS A RESULT OF THE ENSEMBLE SPREAD, AND WILL LIKELY NEED
REFINEMENT AS TRENDS EMERGE IN ENSEMBLE GUIDANCE.
OGOREK
AVIATION /00Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 640 PM CDT WED JUL 30 2025
THE MAIN CONCERNS FOR THE 00Z TAF PERIOD INCLUDE:
* ANOTHER ROUND OF SHOWERS, HEAVY AT TIMES, THIS EVENING AND
THROUGH THE NIGHT, POSSIBLY STRETCHING INTO THURSDAY MORNING.
* MVFR CIGS INTO THURSDAY WITH PERIODS OF IFR POSSIBLE,
ESPECIALLY AT RFD
* NE WINDS GUSTING TO 20 TO 25 KT TONIGHT
ANOTHER ROUND OF DENSELY SCATTERED SHOWERS IS PUSHING INTO
CHICAGOLAND EARLY THIS EVENING. RAIN SHOULD ARRIVE AT ORD AT MDW
BETWEEN 00 AND 01Z. EMBEDDED THUNDER CANNOT BE RULED OUT INTO
MID-EVENING, BUT IS NOT VERY LIKELY. MVFR VSBYS ARE EXPECTED
WITH THE RAIN THROUGH THE EVENING BEFORE THEY SHOULD LARGELY
IMPROVE OVERNIGHT. RAIN COVERAGE WILL BECOME MORE SCATTERED
OVERNIGHT AND MAY DEPART AS EARLY AS THE PREDAWN HOURS, BUT
SHOWERS COULD LINGER WELL PAST DAYBREAK.
MVFR CIGS HAVE TAKEN HOLD AROUND THE AREA AND ARE LIKELY TO
REMAIN INTO THURSDAY WITH AN EXPECTED RETURN TO VFR IN THE LATE
MORNING OR EARLY AFTERNOON. PERIODIC TRIPS DOWN TO IFR WILL BE
POSSIBLE, ESPECIALLY DURING THE EVENING HOURS. IFR IS SEEMINGLY
MOST LIKELY AT RFD THIS EVENING.
MEANWHILE, NE WINDS WILL GUST TO BETWEEN 20 AND 25 KT THIS
EVENING AND OVERNIGHT, WITH SIMILAR WINDS EXPECTED DURING THE
DAY ON THURSDAY.
DOOM
LOT WATCHES/WARNINGS/ADVISORIES
IL...BEACH HAZARDS STATEMENT THROUGH FRIDAY AFTERNOON FOR ILZ006-
ILZ103-ILZ104.
FLOOD WATCH UNTIL 4 AM CDT THURSDAY FOR ILZ019-ILZ020-ILZ021-
ILZ023-ILZ032-ILZ033-ILZ039-ILZ106-ILZ107-ILZ108.
IN...BEACH HAZARDS STATEMENT THROUGH FRIDAY AFTERNOON FOR INZ001-
INZ002.
FLOOD WATCH UNTIL 4 AM CDT /5 AM EDT/ THURSDAY FOR INZ001-
INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY UNTIL 9 AM CDT FRIDAY FOR THE IL AND IN
NEARSHORE WATERS.
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