506
FXUS63 KLOT 222330 CCA
AFDLOT
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
630 PM CDT TUE SEP 22 2026
KEY MESSAGES
- WIDELY SCATTERED SHOWERS MAY PERSIST OVERNIGHT.
- GENERALLY SLIGHTLY BELOW TO BELOW AVERAGE TEMPERATURES
EXPECTED INTO AT LEAST THE FIRST PART OF THE UPCOMING
WEEKEND.
DISCUSSION
ISSUED AT 210 PM CDT TUE SEP 22 2026
WATER VAPOR IMAGERY EARLY THIS AFTERNOON SHOWS A COMPACT, BUT
WELL DEFINED CLOSED MID-UPPER LEVEL LOW OVER EASTERN IA AND
NORTHWEST IL. THIS SYSTEM HAS BEEN A BIT SLOWER TO WEAKEN AND
DEVOLVE INTO AN OPEN WAVE THAN GUIDANCE PROGGED YESTERDAY. THE
18Z SOUNDING THAT JUST CAME IN FROM DVN DEPICTS A DEEPLY
NEARLY SATURATED TO SATURATED COLUMN WITH A PWAT OF 1.31", WHICH
IS NOTABLY MORE MOISTURE THAN DEPICTED IN MOST GUIDANCE
YESTERDAY. THE LIKELY STRONGER FORCING WITH THE MORE DEFINED
MID-UPPER LOW COMBINED WITH GREATER MOISTURE HAS RESULTED IN A
GREATER COVERAGE OF SHOWERS AND EVEN A COUPLE OF ISOLATED
THUNDERSTORMS THIS AFTERNOON INTO THE WESTERN HALF OUR CWA.
TRICKY FORECAST FOR THE NEXT 12-18 HOURS WITH GUIDANCE
CONTINUING TO LARGELY KEEP RAIN CHANCES MINIMAL AND QUICKLY
WEAKENING AND OPENING UP THIS SYSTEM. CERTAINLY NOT SEEING ANY
EVIDENCE IN WATER VAPOR IMAGERY OF IMMINENT WEAKENING, AND
GUIDANCE'S THE POOR HANDLING OF THIS FEATURE OVER THE PAST 24
HOURS THERE IS REASON TO BE SKEPTICAL THAT THE SHOWERS OUT THERE
WILL IMMINENTLY DRY UP. RECENT ACARS SOUNDINGS FROM MDW DO
DEPICT A PRETTY STOUT DRY LAYER BETWEEN 900 AND 700 MB, SO IT IS
PLAUSIBLE THERE WILL BE A DECREASE IN SHOWERS AS IT MOVES EAST.
GIVEN THE POCKET OF MOISTURE EVIDENT IN LOW AND MID LEVEL WATER
VAPOR IMAGERY WITH THE CORE OF THE UPPER LOW, THINK IT IS
PRUDENT TO MAINTAIN RESPECTABLE SHOWER CHANCES INTO TONIGHT
NEAR THE CORE OF THIS UPPER LOW AS IT MOVES ACROSS THE AREA.
ONCE THIS UPPER LOW PUSHES EAST OF THE AREA TOMORROW MORNING, AN
EXTENDED PERIOD OF DRY WEATHER IS EXPECTED FOR THE REMAINDER OF
THE WEEK AND LIKELY THROUGH THE UPCOMING WEEKEND. A VERY BLOCKY
UPPER LEVEL PATTERN IS PROGGED TO SET UP ACROSS CENTRAL AND
EASTERN NORTH AMERICA, SO VERY LITTLE DAY TO DAY CHANGE IN OUR
WEATHER IS EXPECTED. BY LATER IN THE WEEKEND INTO EARLY NEXT
WEEK, SOME BREAKDOWN IN THE BLOCKING PATTERN IS POSSIBLE WITH
UPPER RIDGING DEVELOPING EASTWARD. ASSUMING THIS PLAYS OUT AS
PROGGED (LOWER THAN AVG CONFIDENCE GIVEN THE TENDENCY FOR
GUIDANCE TO BREAK DOWN BLOCKING PATTERNS TOO QUICKLY), THEN A
WARNING TREND WOULD TAKE PLACE LATE IN THE WEEKEND INTO EARLY
NEXT WEEK.
- IZZI
AVIATION /00Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 626 PM CDT TUE SEP 22 2026
A SLOW MOVING MID-UPPER LOW WILL CONTINUE TO MEANDER ACROSS
NORTHERN ILLINOIS INTO WEDNESDAY. ASSOCIATED SHOWERS HAVE BEEN
SLOW TO MAKE EASTWARD PROGRESS OVER THE PAST FEW HOURS BUT CAN'T
RULE OUT THE NEED FOR AT LEAST A VCSH MENTION AT SOME POINT
LATE TONIGHT OR WEDNESDAY MORNING BUT CONFIDENCE IN TIMING AND
COVERAGE REMAINS TOO LOW TO INCLUDE WITH THIS UPDATE. GUIDANCE
CONTINUES TO TREND TOWARD CIGS LOWERING TO MVFR ON WEDNESDAY AT
THE CHICAGO AREA TERMINALS AND HAVE CONVERTED THE TEMPO GROUPS
TO A PREVAILING BKN025 AT 12Z WITH THIS UPDATE.
WINDS WILL REMAIN NORTHEASTERLY THROUGH THE PERIOD AROUND 10 KT
WITH GUSTS INTO THE UPPER TEENS EASING WITH SUNSET THIS EVENING
AND RETURNING AFTER DAYBREAK ON WEDNESDAY.
PETR
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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