314
FXUS63 KLOT 201731
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1231 PM CDT SUN SEP 20 2026
KEY MESSAGES
- WIDESPREAD SHOWERS WILL GRADUALLY DIMINISH IN COVERAGE LATE
THIS AFTERNOON. POCKETS OF LIGHT SHOWERS/DRIZZLE MAY CONTINUE
AT TIMES TONIGHT INTO MONDAY MORNING.
- BELOW NORMAL TEMPERATURES THROUGH THE END OF THE WEEK.
DISCUSSION
ISSUED AT 1230 PM CDT SUN SEP 20 2026
A MID-LEVEL SHORTWAVE/CONVECTIVELY AUGMENTED MCV CONTINUES TO
SHIFT EAST DIRECTLY OVERHEAD EARLY THIS AFTERNOON. AT THE
SURFACE, A SYNOPTIC COLD FRONT IS PUSHING SOUTHWARD, WITH GUSTY
NORTHEASTERLY WINDS DEVELOPING IN ITS WAKE. AS THIS MCV/MID-
LEVEL WAVE PRESSES EASTWARD, THE GREATEST COVERAGE OF STEADY
SHOWERS WILL GRADUALLY PUSH EAST INTO INDIANA THROUGH LATE THIS
AFTERNOON. THE LIGHTNING THREAT HAS ENDED FOR LOCALES NORTH OF
I-80, AS THE MAIN ELEVATED INSTABILITY AXIS CONTINUES TO MOVE
SOUTHWARD. CAN'T RULE OUT A FEW BONAFIDE THUNDERSTORMS
DEVELOPING ACROSS OUR FAR SOUTH (FORD - BENTON COUNTIES) THIS
AFTERNOON ALONG THE COLD FRONT. FORECAST EFFECTIVE INFLOW LAYERS
ARE VERY SHALLOW, GREATLY LIMITING AVAILABLE SRH, BUT DEEP
LAYER SHEAR VALUES NEAR 35 KTS COULD POTENTIALLY SUPPORT A FEW
MINI SUPERCELLS. THE WINDOW FOR THIS WILL BE VERY BRIEF, PERHAPS
3-6 PM (IF THAT), WITH THE MAIN POTENTIAL FOCUSING EAST AND
SOUTH OF OUR FORECAST AREA.
SINCE LOW-LEVEL MOISTURE WON'T REALLY GO ANYWHERE TONIGHT,
POCKETS OF LIGHT SHOWERS/DRIZZLE WILL BE POSSIBLE INTO MONDAY
MORNING AS ADDITIONAL VORTICITY MAXIMA MEANDER OVERHEAD. CLOUD
BASES MAY LIFT SUFFICIENTLY MONDAY AFTERNOON TO BRING AN END TO
LINGERING PRECIPITATION, BUT ADDITIONAL DISTURBANCES DRIFTING
ATOP THE FRONTAL ZONE MAY RESULT IN SPORADIC SPRINKLES/LIGHT
PRECIP CHANCES INTO TUESDAY. PERSISTENT STRONG NORTHEASTERLY
WINDS WILL RESULT IN A PROLONGED PERIOD OF DANGEROUS SWIMMING
CONDITIONS AT AREA BEACHES DUE TO HIGH WAVES AND STRONG
CURRENTS.
THEREAFTER, WE'LL GET A NOTABLE INJECTION OF DRIER AIR FROM THE
EAST AS HIGH PRESSURE SETTLES ACROSS THE UPPER MIDWEST AND
GREAT LAKES REGION THROUGH THE MID AND END OF THE WEEK.
SEASONABLY COOL AND PLEASANT CONDITIONS LOOK TO PREVAIL DURING
THIS PERIOD, WITH HIGH TEMPERATURES GENERALLY IN THE 60S WITH A
VERY MODEST WARMING TREND INTO WEEK'S END. UPPER-LEVEL BLOCKING
LOOKS LIKE IT'LL HOLD MOST PRECIPITATION CHANCES TO A MINIMUM,
AT LEAST UNTIL NEXT WEEKEND WHEN A SMALL SIGNAL FOR
PRECIPITATION CHANCES MAY RETURN.
CARLAW
AVIATION /18Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 1230 PM CDT SUN SEP 20 2026
FORECAST CONCERNS FOR THE TERMINALS...
- LINGERING SHOWERS AND DRIZZLE THROUGH EARLY EVENING, SHOWERS
MAY RESULT IN BRIEF VISIBILITY REDUCTIONS.
- IFR CEILINGS THIS AFTERNOON TO GRADUALLY LIFT TOWARDS MVFR
THIS EVENING AND OVERNIGHT. VFR CONDITIONS NOT EXPECTED TO
RETURN UNTIL MONDAY AFTERNOON AT THE EARLIEST.
- BREEZY NORTHEAST WINDS GUSTING 20-25 KTS THROUGH THE TAF
PERIOD.
BANDS OF RAIN SHOWERS AND DRIZZLE CONTINUE TO PIVOT AROUND A
CONVECTIVE SURFACE LOW IN NORTHWEST IL. THESE SHOWERS/DRIZZLE
ARE EXPECTED TO PERSIST THROUGH EARLY EVENING BEFORE
PRECIPITATION EASES. HOWEVER, THERE IS A GROWING CONCERN THAT
SOME LINGERING LOW-LEVEL MOISTURE IN THE PRESENCE OF WEAK ASCENT
MAY CONTINUE TO DEVELOP INSTANCES OF DRIZZLE THROUGH MONDAY
MORNING. SINCE CONFIDENCE ON DRIZZLE COVERAGE IS LOW HAVE OPTED
TO MAINTAIN A DRY FORECAST AFTER 03Z, BUT DID ADD A FEW009
MENTION TO THE TAFS TO TEASE THE POTENTIAL FOR DRIZZLE.
REGARDLESS, IFR CEILINGS ARE EXPECTED TO PERSIST THROUGH EARLY
EVENING BEFORE GRADUALLY LIFTING TO MVFR OVERNIGHT PENDING ANY
OF THE AFOREMENTIONED DRIZZLE. MVFR CEILINGS ARE FORECAST TO
PERSIST THROUGH MUCH OF MONDAY MORNING BEFORE SKIES ATTEMPT TO
LIFT TO VFR MONDAY AFTERNOON. THOUGH, CONFIDENCE ON WHEN VFR
CONDITIONS RETURN IS LOW AT THIS TIME. OTHERWISE, EXPECT BREEZY
NORTHEAST WINDS TO PREVAIL THROUGH THE TAF PERIOD WITH GUSTS
GENERALLY IN THE 20-25 KT RANGE.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...BEACH HAZARDS STATEMENT THROUGH TUESDAY EVENING FOR ILZ006-
ILZ103-ILZ104.
FLOOD WATCH UNTIL 1 PM CDT THIS AFTERNOON FOR ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ103-
ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.
IN...BEACH HAZARDS STATEMENT THROUGH TUESDAY EVENING FOR INZ001.
FLOOD WATCH UNTIL 1 PM CDT THIS AFTERNOON FOR INZ001-INZ002.
BEACH HAZARDS STATEMENT THROUGH MONDAY MORNING FOR INZ002.
LM...SMALL CRAFT ADVISORY UNTIL 7 PM CDT TUESDAY FOR WINTHROP
HARBOR IL TO BURNS HARBOR IN.
SMALL CRAFT ADVISORY UNTIL 7 AM CDT MONDAY FOR BURNS HARBOR TO
MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page