839
FXUS63 KLOT 301136
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
636 AM CDT WED JUL 30 2025
KEY MESSAGES
- FLOOD WATCH IN EFFECT FROM 1 PM CDT TODAY THROUGH 1 PM CDT
THURSDAY.
- PERIODS OF THUNDERSTORMS TODAY THROUGH THURSDAY MORNING, SOME
POSSIBLY STRONG TO SEVERE WITH TORRENTIAL RAIN WHICH COULD
LEAD TO LOCALIZED FLASH FLOODING.
- POSSIBLE PERIOD OF PROLONGED HEAVY RAIN TONIGHT INTO EARLY
THURSDAY MORNING.
- DANGEROUS SWIMMING CONDITIONS AT LAKE MICHIGAN BEACHES THIS
AFTERNOON THROUGH FRIDAY.
DISCUSSION
ISSUED AT 358 AM CDT WED JUL 30 2025
THROUGH THURSDAY:
MAIN FORECAST CONCERNS FOCUS ON PERIODS OF THUNDERSTORMS TODAY
THROUGH TONIGHT, SOME OF WHICH MAY PRODUCE SEVERE WEATHER AND
TORRENTIAL RAINFALL AND POTENTIAL FLOODING. INCREASING NORTHEAST
WINDS WILL ALSO PRODUCE HAZARDOUS SWIMMING CONDITIONS ON LAKE
MICHIGAN LATER TODAY INTO FRIDAY.
EARLY MORNING WATER VAPOR IMAGERY DEPICTS A CONVECTIVELY-
ENHANCED MID-LEVEL SHORT WAVE TROUGH ACROSS THE CENTRAL PLAINS.
THIS WAVE IS PROGGED TO MOVE SLOWLY EAST ACROSS THE REGION LATER
TODAY INTO THURSDAY, AND WILL AID IN PRODUCING MULTIPLE ROUNDS
OF SHOWERS AND THUNDERSTORMS AS IT TRACKS ALONG A WEST TO EAST
ORIENTED LOW-LEVEL BAROCLINIC ZONE AND INSTABILITY GRADIENT.
REGIONAL RADAR IMAGERY DEPICTS AN AREA OF THUNDERSTORM FROM
NORTHEAST KS INTO SOUTHWEST WI EARLY THIS MORNING, WITH AT LEAST
A COUPLE OF EMBEDDED MCVS WORKING THEIR WAY EAST ACROSS IA.
HIGH-RES GUIDANCE HAS BEEN SOMEWHAT POOR IN DEPICTING THE
EASTERN EXTENT AND TIMING WITH STORMS OVER EASTERN IA, THOUGH
THE GENERAL EXPECTATION IS THAT THE MCS OVER NORTHEAST IA WILL
MOVE INTO OUR NORTHWESTERN CWA AROUND SUNRISE, AND TRACK MAINLY
ALONG/NORTH OF I-88 THROUGH MID-MORNING WITH SOME WEAKENING
LIKELY GIVEN MORE STABLE LOW-LEVELS WITH EASTWARD EXTENT.
SPC/RAP MESOANALYSIS DEPICTS 30-35 KTS OF EFFECTIVE SHEAR, WHICH
ALONG WITH THE MCV MAY ALLOW FOR SOME CONTINUED ORGANIZATION
AND GUSTY SURFACE WIND THREAT.
TRAILING MCS(S) ACROSS IA/NORTHERN MO ARE THEN EXPECTED TO MOVE
INTO THE AREA LATER THIS MORNING/MIDDAY. GENERAL INCREASE IN
SYNOPTIC FORCING AHEAD OF THE APPROACHING SHORT WAVE, PRESENCE
OF UPPER LEVEL DIVERGENCE BENEATH THE RIGHT ENTRANCE TO A 100+
KT 250 MB JET STREAK ACROSS THE UPPER MIDWEST/NORTHERN LAKES AND
INCREASING DIURNAL INSTABILITY SHOULD SUPPORT ADDITIONAL
CLUSTERS OF STORMS DURING THE AFTERNOON AND INTO TONIGHT. WHILE
SOME POTENTIAL FOR DAMAGING WINDS WILL EXIST (WET
DOWNBURSTS/MICROBURSTS), THESE REPEATED ROUNDS OF STORMS IN A
VERY MOIST ENVIRONMENT RAISE THE CONCERN FOR INCREASED FLOODING
POTENTIAL. FORECAST PRECIPITABLE WATER VALUES INCREASE INTO THE
2-2.50" RANGE (ABOUT AS HIGH AS THEY GET PER SPC DVN/ILX
SOUNDING CLIMATOLOGY) INTO TONIGHT, WHICH SHOULD SUPPORT VERY
EFFICIENT RAIN PRODUCING STORMS. WHILE EXACT TRACK PLACEMENT IS
UNCERTAIN, STORM CLUSTERS MAY EASILY PRODUCE 1-2 INCHES OF RAIN,
AND THIS COULD LEAD TO PERHAPS LOCALLY 3-5 INCHES WHERE STORMS
REPEATEDLY TRACK OVER THE SAME AREA. WITH THIS IN MIND HAVE
HOISTED A FLOOD WATCH FOR THE ENTIRE FORECAST AREA FROM 18Z
TODAY THROUGH 18Z THURSDAY. SURFACE LOW PRESSURE WAVE (AND THE
SHEARING MID-LEVEL TROUGH AXIS) EVENTUALLY WORKS EAST OF THE
AREA THURSDAY AFTERNOON, ALLOWING THE TRAILING COLD FRONT TO SAG
SOUTH OF THE AREA LATE. THIS SHOULD DECREASE HEAVY RAINFALL
THREAT FROM NORTH TO SOUTH WITH PRECIPITATION EVENTUALLY ENDING.
AS THE SURFACE LOW TRACKS EAST TODAY, AND SURFACE HIGH PRESSURE
BUILDS ACROSS THE UPPER MIDWEST AND NORTHERN LAKES, SURFACE
WINDS WILL TURN NORTHEASTERLY AND BECOME BREEZY FROM THIS
AFTERNOON INTO TONIGHT AND THURSDAY. WINDS MAY GUST AS HIGH AS
30-35 MPH TONIGHT, ESPECIALLY NEAR LAKE MICHIGAN. THESE WINDS
WILL BUILD WAVES ON THE LAKE THAT WILL MAKE FOR DANGEROUS
CURRENTS AND SWIMMING CONDITIONS. BEACH HAZARD STATEMENTS ARE
ALREADY IN EFFECT FOR THIS.|
RATZER
THURSDAY NIGHT THROUGH TUESDAY:
A BROAD SURFACE HIGH IS EXPECTED TO BE PARKED OVER THE GREAT
LAKES THURSDAY NIGHT AND REMAIN IN PLACE THROUGH THE WEEKEND. AS
A RESULT, DRY CONDITIONS WITH PLENTIFUL SUNSHINE ARE IN STORE
FOR US. AS AN ADDED BONUS, PERSISTENT NORTHWEST FLOW ALOFT ON
THE BACK SIDE OF AN UPPER TROUGH OVER THE NORTHEAST CONUS AND
NORTHEAST WINDS AT THE SURFACE WILL KEEP TEMPERATURES AND
HUMIDITY IN A MORE COMFORTABLE RANGE WITH DAILY HIGHS IN THE
MID-70S TO AROUND 80 AND OVERNIGHT LOWS IN THE 50S TO AROUND 60.
HOWEVER, BREEZIER WINDS ARE LIKELY TO PERSIST THROUGH FRIDAY
EVENING ESPECIALLY OVER THE OPEN WATERS OF LAKE MICHIGAN WHICH
WILL RESULT IN CONTINUED HIGH WAVES AND LIFE THREATENING RIP
CURRENTS AT AREA BEACHES. WHILE OUR CURRENT BEACH HAZARD
STATEMENT RUNS THROUGH FRIDAY AFTERNOON, THERE IS A CHANCE WE
MAY NEED TO EXTEND IT IF THE FORECAST CONTINUES TO TREND AS
EXPECTED. THAT SAID, ANYONE WITH PLANS TO HEAD TO THE BEACH
FRIDAY SHOULD PLAN ON STAYING OUT OF THE WATER UNTIL WINDS AND
WAVES SUBSIDE.
HEADING INTO NEXT WEEK, THE DRY WEATHER DOES LOOK TO LINGER
THROUGH AT LEAST MONDAY BEFORE THE UPPER PATTERN SHIFTS BACK TO
AN ACTIVE SOUTHWEST FLOW REGIME TOWARDS THE MIDDLE OF THE WEEK.
THIS PATTERN SHIFT WILL RESULT IN TEMPERATURES AND HUMIDITY
LEVELS RETURNING TO MORE TYPICAL AUGUST READINGS (HIGHS IN THE
80S AND DEW POINTS IN THE 60S TO NEAR 70) AND OF COURSE CHANCES
FOR SHOWERS AND THUNDERSTORMS. WHILE THERE IS SOME UNCERTAINTY
AS TO WHEN EXACTLY THE RAIN RETURNS, IT LOOKS LIKE CHANCES WILL
BE INCREASING MONDAY NIGHT ONWARD.
YACK
AVIATION /12Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 636 AM CDT WED JUL 30 2025
AVIATION FORECAST CONCERNS FOR THE 12Z TAFS:
- COUPLE OF ROUNDS OF SHRA/TSRA THIS MORNING THROUGH EARLY THIS
AFTERNOON.
- ADDITIONAL PERIODS OF SHOWERS AND PROBABLY SOME EMBEDDED TS
THROUGH TONIGHT, THOUGH LOW CONFIDENCE IN COVERAGE AND TIMING
OF TS.
- MVFR CEILINGS EXPECTED THIS AFTERNOON, WITH A PERIOD OF IFR
CEILINGS LIKELY TONIGHT INTO THURSDAY MORNING.
- WINDS TURN NORTHEAST AND BECOME BREEZY THIS AFTERNOON THROUGH
THE END OF THE PERIOD, WITH GUSTS 20-25 KTS.
TWO THUNDERSTORM COMPLEX ARE PUSHING EAST ACROSS EASTERN IA AND
NORTHERN IL EARLY THIS MORNING. THE FIRST IS IMPACTING RFD NOW,
AND SHOULD REACH THE CHICAGO TERMINALS BY AROUND 13Z. SOME
WEAKENING IS EXPECTED AS LOW-LEVEL INSTABILITY DECREASE WITH
EASTWARD EXTENT, THOUGH AT LEAST ISOLATED THUNDER IS EXPECTED.
THERE MAY BE A COUPLE HOUR BREAK BETWEEN THE FIRST COMPLEX, AND
THE LINE OF STORMS CURRENTLY OVER EASTERN IA. EXTRAPOLATION OF
CURRENT MOVEMENT BRINGS TS CHANCES BACK INTO RFD AROUND 15Z AND
INTO THE CHICAGO TERMINALS BY 17Z. LOW CONFIDENCE IN TREND
DETAILS, THOUGH SOME DIURNAL WARMING WOULD SUPPORT THIS LINE
CONTINUING TO MOVE THROUGH THE AREA. MAY BE A PERIOD OF GUSTY
WESTERLY WINDS WITH THESE STORMS.
BEYOND MID-AFTERNOON, CONFIDENCE REALLY DECREASES WITH TS
COVERAGE AND TIMING INTO TONIGHT. APPROACHING MID-LEVEL WAVE
SHOULD SUPPORT ADDITIONAL DEVELOPMENT OF PERIODS OF SHOWERS AND
POSSIBLY EMBEDDED TS INTO THURSDAY AM, THOUGH CONFIDENCE ON
TIMING ANY BETTER MENTIONS OF TS IS VERY LOW. HAVE MAINTAINED
SHRA/RA THROUGH THE PERIOD WITH LATER UPDATES BETTER ABLE TO
TARGET ANY TS PERIODS.
WINDS WILL TURN NORTHEASTERLY THIS AFTERNOON AND WILL BECOME
BREEZY WITH GUSTS 20-25 KT LATE TODAY THROUGH THURSDAY MORNING.
THE COMBINATION OF SHRA/RA AND COOLER NORTHEAST FLOW SHOULD
SUPPORT DEVELOPMENT OF MVFR CIGS LATER THIS AFTERNOON, WITH A
PERIOD OF IFR CIGS LIKELY TONIGHT INTO EARLY THURSDAY.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH THURSDAY
AFTERNOON FOR ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-
ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.
BEACH HAZARDS STATEMENT FROM 1 PM CDT THIS AFTERNOON THROUGH
FRIDAY AFTERNOON FOR ILZ006-ILZ103-ILZ104.
IN...FLOOD WATCH FROM 1 PM CDT /2 PM EDT/ THIS AFTERNOON THROUGH
THURSDAY AFTERNOON FOR INZ001-INZ002-INZ010-INZ011-INZ019.
BEACH HAZARDS STATEMENT FROM 1 PM CDT THIS AFTERNOON THROUGH
FRIDAY AFTERNOON FOR INZ001-INZ002.
LM...SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 9 AM CDT
FRIDAY FOR THE IL AND IN NEARSHORE WATERS.
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