200
FXUS63 KLOT 221147
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
647 AM CDT TUE SEP 22 2026
KEY MESSAGES
- SPOTTY SPRINKLES/LIGHT SHOWERS POSSIBLE IN SOME AREAS TODAY.
- BELOW AVERAGE TEMPERATURES EXPECTED FOR THE REMAINDER OF THE
WORK WEEK.
DISCUSSION
ISSUED AT 159 AM CDT TUE SEP 22 2026
LATEST SURFACE ANALYSIS PLACES A BROAD ~1030 MB SURFACE HIGH
FROM THE NORTHERN GREAT LAKES EASTWARD INTO QUEBEC. THE WESTERN
PERIPHERY OF THE HIGH IS PROGGED TO STRENGTHEN ACROSS THE
NORTHERN LAKES TODAY, IN ASSOCIATION WITH STRONG SUBSIDENCE AND
BUILDING MID-LEVEL HEIGHTS IN THE WAKE OF A POSITIVE-TILT SHORT
WAVE DIGGING SOUTHEAST ACROSS THE NORTHEASTERN CONUS. FARTHER TO
THE SOUTHWEST, A SLOW- MOVING CLOSED UPPER-LEVEL LOW WAS
EVIDENT IN GOES VAPOR IMAGERY OVER EASTERN IA. THIS FEATURE IS
FORECAST TO CONTINUE TO DRIFT SLOWLY EAST-SOUTHEAST ACROSS
NORTHERN IL THROUGH THIS EVENING AND EVENTUALLY INTO CENTRAL IN
WEDNESDAY MORNING, FORMING A REX BLOCK (UPPER LEVEL HIGH
POLEWARD OF AN UPPER LEVEL LOW) WHICH WILL ONLY GRADUALLY SHIFT
EAST THROUGH MID-WEEK.
CURRENT REGION RADAR IMAGERY DEPICTS SHOWERS (WITH EVEN SOME
ISOLATED LIGHTNING STRIKES) ASSOCIATED WITH THE AFOREMENTIONED
CIRCULATION OVER EASTERN IA AND VICINITY. THESE SHOWERS WILL
GRADUALLY DRIFT EAST WITH THE CIRCULATION TODAY, ALTHOUGH
THEY'LL BE ENCOUNTERING GRADUALLY DRIER AIR WITH EASTWARD
EXTENT. WOULD EXPECT AT LEAST SOME SPOTTY PRECIPITATION TO
SPREAD INTO THE FORECAST AREA HOWEVER, AND HAVE ADDED SOME
SLIGHT CHANCE POPS (15-20% - HIGHEST WEST) DEVELOPING FROM WEST
TO EAST TODAY/EARLY THIS EVENING THOUGH COVERAGE MAY BE ISOLATED
IN MANY AREAS UNDER OTHERWISE MOSTLY CLOUDY SKIES. SPOTTY,
LIGHT SHOWER CHANCES SHOULD DIMINISH FROM WEST TO EAST ACROSS
NORTHERN THIS EVENING AS THE MID-LEVEL CIRCULATION CONTINUES TO
DRIFT EAST, AND ACROSS NORTHWEST INDIANA OVERNIGHT, THOUGH
PROBABLY CAN'T COMPLETELY RULE OUT A FEW STRAY SPRINKLES FROM
THE WESTERN FRINGES OF THIS DISTURBANCE EVEN INTO WEDNESDAY
MORNING. AS PREVIOUS DAY SHIFT NOTED, THERE IS A BIT OF A SIGNAL
IN GUIDANCE FOR SLIGHTLY BETTER LOW-LEVEL LAPSE RATES OVER LAKE
MICHIGAN ON WEDNESDAY WHICH COULD SUPPORT SOME LAKE-EFFECT
SPRINKLES OR LIGHT SHOWERS INTO NORTHEAST IL, THOUGH DELTA-TS
ARE MARGINAL (10-12C) AND INVERSION HEIGHTS ARE NEAR/JUST BELOW
5 KFT. THUS CHANCES CONTINUE TO APPEAR FAIRLY LOW AND KEPT ONLY
SUB-15% POPS WITHOUT A PRECIP MENTION NEAR THE LAKE FOR THIS
POSSIBILITY.
OTHERWISE, WITH THE RELATIVELY STRONG SURFACE HIGH OFF TO OUR
NORTHEAST, BREEZY/BLUSTERY (GUSTING 20-25 KTS AT TIMES,
ESPECIALLY NEAR THE LAKE) NORTHEAST WINDS WILL CONTINUE ACROSS
THE AREA INTO WEDNESDAY BEFORE DIMINISHING MORE SUBSTANTIALLY.
THIS WILL MAINTAIN DANGEROUS SWIM CONDITIONS (AND CURRENT BEACH
HAZARD STATEMENTS IN EFFECT) FOR OUR LAKE MICHIGAN BEACHES, AS
WELL AS COOLER THAN NORMAL TEMPERATURES THROUGH MID-WEEK.
DAYTIME HIGHS ARE EXPECTED TO REMAIN IN THE 60S WITH OVERNIGHT
LOWS IN THE 50S IN MOST SPOTS, THOUGH SOME LATE NIGHT 40S ARE
POSSIBLE AWAY FROM THE LAKE WHERE BREAKS IN THE CLOUDS OR MORE
WIDESPREAD SCATTERING OCCURS.
EVENTUALLY, THE REX BLOCK IS PROGGED TO BREAK DOWN IN THE
THURSDAY AND FRIDAY TIME PERIOD, ALLOWING UPPER-LEVEL RIDGING TO
EXTEND INTO THE UPPER MISSISSIPPI VALLEY/WESTERN LAKES. THIS
WILL ALLOW FOR A MODEST WARMING TREND INTO THE LOW 70S AND UPPER
60S, LIGHTER WINDS AND POSSIBLY MORE SUNSHINE. MEDIUM-RANGE
GUIDANCE CONTINUES TO DEPICT INCREASING PRECIP CHANCES WEST OF
THE MISSISSIPPI BY FRIDAY HOWEVER, WHICH MAY AT LEAST SPREAD
MID/HIGH-LEVEL CLOUD COVER BACK ACROSS THE REGION. CURRENT
GLOBAL MODELS/ENSEMBLES SUGGEST PRECIP MAY TRY TO PUSH INTO THE
FORECAST AREA BY LATE SATURDAY/SUNDAY, THOUGH WITH GUIDANCE
DEVELOPING A DEEP TROUGH/CLOSED LOW TO OUR EAST ALONG THE
ATLANTIC COAST, THE EASTWARD PROGRESSION OF ANY SUBSTANTIAL
PRECIPITATION THREAT MAY BE SOMEWHAT BLOCKED UNTIL BEYOND THE
END OF THE CURRENT FORECAST PERIOD.
RATZER
AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 647 AM CDT TUE SEP 22 2026
FORECAST CONCERNS INCLUDE...
CHANCE OF SHOWERS THIS MORNING AND AGAIN TONIGHT.
POSSIBLE MVFR CIGS, MAINLY TONIGHT/WEDNESDAY MORNING.
GUSTY EAST/NORTHEAST WINDS THROUGH THIS EVENING.
SHOWERS CURRENTLY ACROSS NORTHWEST IL AND RFD ARE EXPECTED TO
PERSIST THROUGH AT LEAST MID MORNING WITH ADDITIONAL SHOWERS
POSSIBLE INTO THIS AFTERNOON ACROSS NORTHWEST IL. AN ISOLATED
THUNDERSTORM IS ALSO POSSIBLE OVER THE NEXT FEW HOURS.
CONFIDENCE IS LOW FOR SHOWERS FURTHER EAST AND ACROSS THE
CHICAGO TERMINALS. THERE IS SOME DRY AIR IN THE LOW LEVELS THAT
MAY ALLOW MOST OF THIS ACTIVITY TO REMAIN WEST OF THE CHICAGO
TERMINALS BUT MAINTAINED PROB MENTION FOR THIS MORNING FOR NOW.
ADDITIONAL SHOWERS ARE POSSIBLE THIS EVENING AND OVERNIGHT BUT
CONFIDENCE IS LOW AND NO MENTION WITH THIS FORECAST.
MVFR CIGS EARLIER THIS MORNING HAVE SCATTERED OUT AND NO LONGER
EXPECTING MVFR CIGS THIS MORNING. MVFR CIGS MAY REDEVELOP LATER
TONIGHT INTO WEDNESDAY MORNING BUT CONFIDENCE HAS DECREASED AND
HAVE INCLUDED ONLY SCATTERED MENTION.
EAST/NORTHEAST WINDS MAY GUST IN THE LOWER 20KT RANGE TODAY AND
INTO THIS EVENING. GUSTS WILL END FOR MOST LOCATIONS THIS
EVENING, THOUGH GUSTS INTO THE 15-20KT RANGE WILL BE POSSIBLE
FOR THE CHICAGO TERMINALS. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...BEACH HAZARDS STATEMENT THROUGH WEDNESDAY EVENING FOR ILZ006-
ILZ103-ILZ104.
IN...BEACH HAZARDS STATEMENT THROUGH WEDNESDAY AFTERNOON FOR INZ001-
INZ002.
LM...SMALL CRAFT ADVISORY UNTIL 7 PM CDT WEDNESDAY FOR THE IL
NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 10 AM CDT WEDNESDAY FOR CALUMET
HARBOR IL TO BURNS HARBOR IN.
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