308
FXUS63 KLOT 220535
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1235 AM CDT TUE SEP 22 2026
KEY MESSAGES
- BELOW AVERAGE TEMPERATURES EXPECTED FOR THE REMAINDER OF THE
WORK WEEK.
DISCUSSION
ISSUED AT 155 PM CDT MON SEP 21 2026
A STRONG (1031 MB) HIGH OVER LAKE SUPERIOR IS HELPING PRODUCE RATHER
BRISK NORTHEAST WINDS WHICH HAVE BEEN USHERING IN COOLER
TEMPERATURES AND GRADUALLY LOWER DEWPOINTS. A CLOSED MID-UPPER LEVEL
LOW SEEN ON WATER VAPOR IMAGERY IS MOVING INTO WESTERN IA EARLY THIS
AFTERNOON. THIS UPPER LOW IS EXPECTED TO SLOWLY WEAKEN AS IT PUSHES
EAST INTO NORTHERN IL BY MIDDAY TUESDAY. THE UNSEASONABLY MOIST AIR
MASS THAT HELPED FEED HEAVY RAINFALL TOTALS OVER THE WEEKEND IS
BEING SHUNTED OFF TO THE SOUTH OF THE AREA. HOWEVER, COLD MID-LEVEL
TEMPS (AROUND -15C) ASSOCIATED WITH THIS WEAKENING UPPER LOW SHOULD
BE ENOUGH TO RESULT IN SCATTERED SHOWERS THIS AFTERNOON ACROSS IA.
THIS SHOWER ACTIVITY IS EXPECTED TO ATTEMPT TO SPREAD EAST INTO
NORTHERN IL LATE TONIGHT INTO TUESDAY MORNING AS THE UPPER LOW
PUSHES THIS WAY, HOWEVER, THE SHOWERS ARE EXPECTED TO ENCOUNTER A
GRADUALLY DRIER AIR MASS AS THEY MOVE EAST OF THE MS RIVER. HAVE
MAINTAINED SOME 20-30% CHANCES FOR SHOWERS LATE TONIGHT INTO TUESDAY
AM, ESPECIALLY ACROSS OUR WESTERN CWA.
THIS SHORTWAVE TROUGH IS PROGGED TO CONTINUE EASTWARD TOWARD THE
EAST COAST BY WEDNESDAY INTO WEDNESDAY NIGHT, LIKELY AIDING IN
INTENSE COASTAL CYCLOGENESIS. A REX BLOCK IS EXPECTED TO DEVELOP
OVER SOUTHEASTERN CANADA INTO THE GREAT LAKES LATER THIS WEEK AS A
STRONG, LARGE CUT-OFF COASTAL CYCLONE BECOMES QUASI-STATIONARY TO
THE SOUTH OF A STRONG MID-UPPER HIGH OVER SOUTHEASTERN CANADA. FOR
OUR AREA, THIS SHOULD RESULT IN AN EXTENDED PERIOD OF SOMEWHAT
COOLER TEMPERATURES AND VERY LITTLE THREAT OF PRECIPITATION FROM MID
WEEK THROUGH THE UPCOMING WEEKEND. ONE SMALL POSSIBLE EXCEPTION TO
THE DRY WEATHER COULD BE WEDNESDAY MORNING INTO THE CHICAGO METRO
AREA WHEN THERE COULD BE A FEW SPRINKLES OR VERY LIGHT LAKE EFFECT
RAIN SHOWERS. THERMODYNAMICS ARE MARGINAL AND WITH FAIRLY DRY LOW
LEVEL AIR MASS, THE CHANCES APPEAR PRETTY SMALL SO DIDN'T INTRODUCE
ANY PRECIP INTO THE GRIDS AT THIS TIME, BUT DID NUDGE POPS UP TO
AROUND 10%. OTHERWISE, LOOK FOR TEMPERATURES THAT WILL LIKELY SLOWLY
MODERATE LATE IN THE WEEK INTO THE WEEKEND WITH TEMPERATURES
PROBABLY WARMING BACK INTO THE 70S.
- IZZI
AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 1235 AM CDT TUE SEP 22 2026
FORECAST CONCERNS INCLUDE...
MVFR CIGS THROUGH MID/LATE MORNING AND AGAIN EARLY WEDNESDAY.
LOW CHANCES FOR SHOWERS THROUGH THE PERIOD.
GUSTY EAST/NORTHEAST WINDS.
MVFR CIGS CONTINUE TO DEVELOP ACROSS NORTHEAST IL AND SOUTHERN
WI EARLY THIS MORNING AND ARE EXPECTED TO CONTINUE THROUGH AT
LEAST MID MORNING, THOUGH THERE REMAINS UNCERTAINTY FOR HOW
PREVAILING THEY WILL REMAIN. GIVEN CURRENT TRENDS, OPTED TO
CARRY MVFR CIGS AND WILL MONITOR TRENDS. THERE IS REASONABLE
CONSENSUS FOR CIGS TO LIFT BY MIDDAY INTO THIS AFTERNOON AND
THEN GUIDANCE IS SUGGESTING MVFR CIGS WILL REDEVELOP LATE
TONIGHT INTO EARLY WEDNESDAY MORNING.
A SLOW MOVING UPPER WAVE CURRENTLY OVER EASTERN IA IS EXPECTED
TO MOVE ACROSS THE TERMINALS LATER THIS MORNING. WHILE
CONFIDENCE IS LOW, THERE APPEARS TO BE A MENTIONABLE CHANCE FOR
SHOWERS DURING THIS TIME PERIOD AND INCLUDED PROB SHOWER MENTION,
THOUGH WHATEVER DOES MATERIALIZE MAY END UP BEING ISOLATED.
THERE WILL BE A BETTER CHANCE FOR SHOWERS ACROSS NORTHWEST IL
AND AT RFD. ADDITIONAL LOW CHANCES FOR SHOWERS ARE POSSIBLE THIS
EVENING AND AGAIN OVERNIGHT INTO WEDNESDAY MORNING. CONFIDENCE
IS TOO LOW TO INCLUDE SHOWER MENTION AT THIS TIME.
EAST/NORTHEAST WINDS WILL REMAIN GUSTY AT TIMES THROUGH THE
PERIOD, MAINLY FOR THE CHICAGO TERMINALS OVERNIGHT AND AGAIN
LATE TONIGHT, AND FOR MOST OF THE ARE DURING THE DAYLIGHT HOURS
TODAY. 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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