597
FXUS63 KLOT 301752
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1252 PM 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.
UPDATE
ISSUED AT 927 AM CDT WED JUL 30 2025
EARLIER THIS MORNING, AN MCV AND ASSOCIATED BAND OF
THUNDERSTORMS MOVED ALONG THE ILLINOIS AND INDIANA BORDER. AN
OUTFLOW BOUNDARY FROM THE DECAYING CONVECTION HAS SINCE STALLED FROM
NEAR CHICAGO SOUTHWESTWARD THROUGH JOLIET TO PONTIAC. THE
AIRMASS SOUTHEAST OF THE OUTFLOW BOUNDARY IS ALREADY UNSTABLE
WITH AIR TEMPERATURES NEAR 80 AND DEW POINTS IN THE MID TO UPPER
70S CONTRIBUTING TO AROUND 2300 J/KG OF MLCAPE (PER THE 12Z ILX
RAOB).
ANOTHER, LARGELY DECAYED, MCS IS CURRENTLY APPROACHING I-39, AND
IS AHEAD OF AN MCV MOVING THROUGH CENTRAL IOWA. AS THE MCS
REACHES THE UNSTABLE AIRMASS (AGAIN EAST OF A LINE FROM PONTIAC
TO JOLIET TO CHICAGO), THE EXPECTATION IS FOR NEW CONVECTION TO
DEVELOP AND/OR ONGOING WEAK CONVECTION TO INTENSIFY. GIVEN ANY
MID-LEVEL WIND MAX AND ASSOCIATED SHEAR ASSOCIATED WITH THE
IOWA MCV WILL BE LAGGING TO THE WEST, ANY THREAT FOR SEVERE
WEATHER WITH RENEWED CONVECTION WOULD BE DEPENDENT ON
AMALGAMATION OF COLD POOLS AND TALL CORES TO SUPPORT LOCALLY
DAMAGING WINDS. SUCH A THREAT APPEARS HIGHEST GENERALLY EAST OF
I-55 BETWEEN 11 AM AND 3 PM.
HAVE NOT HAD A CHANCE TO DO A DEEP DIVE IN TO THE THREAT FOR
ADDITIONAL SHOWERS AND STORMS THIS AFTERNOON AS THE CORE OF THE
MCV MOVES OVERHEAD ALONG A SOUTHWARD-MOVING COLD FRONT.
CONCEPTUALLY, SUCH A PATTERN SHOULD SUPPORT A BAND OF TORRENTIAL
DOWNPOURS SOMEWHERE IN THE GENERAL VICINITY. FOR NOW, WILL
MAINTAIN THE INHERITED FLOOD WATCH AND SAVE ANY CHANGES, IF
NEEDED, FOR THE AFTERNOON FORECAST PACKAGE.
UPDATED PRODUCTS WILL BE SENT SOON.
BORCHARDT
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 /18Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 1235 PM CDT WED JUL 30 2025
CONCERNS:
-SHOWERS AND THUNDERSTORMS THROUGH EARLY-MID AFTERNOON
-IFR OR EVEN BRIEF LIFR VISIBILITY IN HEAVY DOWNPOURS
-POTENTIAL FOR IFR CEILINGS LATER TODAY AND TONIGHT
A COMPLEX OF THUNDERSTORMS WILL CONTINUE TO SLIDE BY JUST TO THE
SOUTH OF THE CHICAGOLAND TERMINALS. KMDW WILL GET GRAZED BY
LIGHTNING, WITH ABOUT A 40-50% PERCENT CHANCE OF DIRECT TERMINAL
IMPACTS, FOR KORD VCTS MORE LIKELY TELLS THE STORY. FOR BOTH
TERMINALS, HEAVY SHOWERS MAY STILL REDUCE VISIBILITY TO IFR (1
1/2-2SM), THOUGH LIFR MAY BRIEFLY OCCUR. THERE WILL BE A BREAK
IN THE RAIN LATER THIS AFTERNOON INTO THE EARLY EVENING, BEFORE
ANOTHER BATCH OF RAIN/SHOWERS WILL SHIFT INTO THE AREA. CEILINGS
WILL LIKELY DROP BACK TO MVFR, WITH A 50% CHANCE OF IFR.
CONFIDENCE ON HOW LONG IFR WILL LAST IS LOW. RAIN WILL TAPER OFF
NORTH TO SOUTH OVERNIGHT. WINDS WILL INCREASE OUT OF THE
NORTHEAST, ESPECIALLY TONIGHT. GUSTS TO 25 KT APPEAR LIKELY AT
TIMES TONIGHT INTO THURSDAY.
KMD
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH 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 THROUGH FRIDAY AFTERNOON FOR ILZ006-
ILZ103-ILZ104.
IN...FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR INZ001-INZ002-
INZ010-INZ011-INZ019.
BEACH HAZARDS STATEMENT THROUGH FRIDAY AFTERNOON FOR INZ001-
INZ002.
LM...SMALL CRAFT ADVISORY UNTIL 9 AM CDT FRIDAY FOR THE IL AND IN
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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