113
FXUS63 KLOT 211855
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
155 PM CDT MON SEP 21 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 /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1216 PM CDT MON SEP 21 2026
THERE ARE NO SIGNIFICANT CONCERNS THROUGH THE PERIOD. CAN'T RULE
OUT OCCASIONAL VFR -RA IN SPOTS THIS AFTERNOON THROUGH TUESDAY
MORNING, BUT WILL ADDRESS AS NEEDED IN SUBSEQUENT UPDATES.
HIGHER END MVFR CIGS AT RFD SHOULD SCATTER THIS AFTERNOON, WITH
PRIMARILY VFR CIGS AT ALL OTHER SITES. BRIEF 2-3KFT AGL CIGS ARE
NOT COMPLETELY OUT OF THE REALM OF POSSIBILITY, AND THUS HELD
WITH SCT025 MENTION IN THE TAFS. WINDS WILL BE STEADY TO AT
TIMES GUSTY FROM THE NORTHEAST THROUGH TUESDAY AFTERNOON.
CASTRO
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.
SMALL CRAFT ADVISORY UNTIL 3 PM CDT THIS AFTERNOON FOR BURNS
HARBOR TO MICHIGAN CITY IN.
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