758
FXUS63 KLOT 122326
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
626 PM CDT MON OCT 12 2026
KEY MESSAGES
- UNSEASONABLE WARMTH CONTINUES INTO TUESDAY, WARMEST SOUTH OF
INTERSTATE 80.
- SHOWERS ARE LIKELY TUESDAY NIGHT INTO WEDNESDAY MORNING AND
MAY BE ACCOMPANIED BY ISOLATED THUNDERSTORMS CAPABLE OF GUSTY
WINDS AND SMALL HAIL.
- WIDESPREAD RAIN IS EXPECTED THURSDAY FOLLOWED BY A STRONG COLD
FRONT AND MUCH COOLER CONDITIONS FRIDAY INTO THE WEEKEND.
DISCUSSION
ISSUED AT 314 PM CDT MON OCT 12 2026
AFTER A BRIEF DELAY IN WARMING DUE TO LINGERING HIGH CLOUDS,
TEMPERATURES HAVE SINCE WARMED WELL INTO THE 80S TO NEAR 90! ACROSS
THE AREA, WITH BOTH CHICAGO-O'HARE AND ROCKFORD HAVING BROKEN
THEIR DAILY HIGH TEMPERATURE RECORDS FOR OCTOBER 12 WITH ANOTHER
HOUR OR SO OF WARMING YET TO GO.
HEADING INTO THE EVENING HOURS, MID-LEVEL WARM ADVECTION AHEAD
OF AN APPROACHING WEAK DISTURBANCE MAY LEAD TO A STRAY SHOWER OR
SPRINKLE DEVELOPING OVER SOUTHEAST WISCONSIN AND OVER LAKE
MICHIGAN. CAN'T FULLY RULE OUT THIS ACTIVITY INITIATING OVER
FAR NORTHEAST ILLINOIS BUT HAVE MAINTAINED A DRY FORECAST WITH
THIS UPDATE (< 15% CHANCE) GIVEN VERY DRY LOW-LEVELS IN PLACE
THIS FAR SOUTH. CONTINUED SOUTHWESTERLY LOW-LEVEL FLOW WILL
KEEP TEMPERATURES IN THE UPPER 60S TO LOWER 70S OVERNIGHT.
A WEAK SURFACE LOW CURRENTLY OVER SOUTHWEST MINNESOTA WILL
CONTINUE TO DRIFT EAST THROUGH CENTRAL WISCONSIN AND NORTHERN
LOWER MICHIGAN BY TUESDAY MORNING. AN ASSOCIATED WEAK SURFACE
TROUGH/FRONT WILL SWING INTO THE AREA AND TURN WINDS WEST TO
NORTHWESTERLY. THIS WILL LIKELY KEEP TEMPERATURES A BIT COOLER
(BUT STILL UNSEASONABLY WARM) FOR AREAS NORTH OF I-80 IN THE MID
70S TO LOWER 80S. FARTHER SOUTH, TEMPERATURES MAY STILL MANAGE
TO WARM INTO THE MID-UPPER 80S.
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS
WEST/NORTHWEST ILLINOIS LATE TUESDAY EVENING AND EXPAND ACROSS
THE AREA INTO THE OVERNIGHT HOURS. THESE STORMS WILL BE ON THE
COLD SIDE OF THE SURFACE FRONT (STALLED OUT OVER CENTRAL IL/IN)
AND WILL BE ELEVATED. WHILE LAPSE RATES ARE NOT OVERLY
IMPRESSIVE, MODEST MUCAPE (1000-1500 J/KG) MAY BRIEFLY OVERLAP
WITH 25-35 KT OF SHEAR WITHIN THAT ELEVATED LAYER. GIVEN
OVERALL WEAKER FORCING, THE POTENTIAL FOR THUNDERSTORMS TO GROW
TALL ENOUGH TO FULLY REALIZE THIS ENVIRONMENT IS ON THE LOWER
SIDE, BUT CAN'T FULLY RULE OUT LOCALLY STRONGER STORMS CAPABLE
OF GUSTY WINDS AND HAIL. IF CONFIDENCE INCREASES IN MORE ROBUST
STORMS THE LEVEL 1 OF 5 THREAT FOR DAMAGING HAIL MAY END UP
NEEDING TO BE EXPANDED FARTHER EAST WITH LATER UPDATES.
AFTER A RELATIVE LULL IN PRECIPITATION LATER IN THE DAY ON
WEDNESDAY ANOTHER MOISTURE LADEN SYSTEM ASSOCIATED WITH ENERGY
EJECTING OFF THE ROCKIES WILL LIFT INTO THE AREA LATE WEDNESDAY
NIGHT THROUGH THURSDAY BRINGING WIDESPREAD SHOWERS AND ANOTHER
CHANCE FOR THUNDERSTORMS. THE SYSTEM WILL LIKELY PHASE WITH AN
APPROACHING VIGOROUS MID-UPPER SHORTWAVE DIVING ACROSS THE UPPER
MIDWEST THAT SENDS A STRONG COLD FRONT ACROSS THE AREA. WHILE
SOME DIFFERENCES REMAIN IN THE OVERALL MAGNITUDE, ENSEMBLES
REMAIN CONSISTENT IN DEPICTING A PERIOD OF MUCH COLDER
CONDITIONS OCCURRING (RELATIVE TO THE NEAR RECORD WARMTH
EARLIER IN THE WEEK). FORECAST OVERNIGHT LOWS FRIDAY AND
SATURDAY ARE IN THE 30S OUTSIDE OF CHICAGO WHICH MAY BRING OUR
FIRST POTENTIAL FOR FROST OF THE SEASON IF THIS TREND HOLDS.
THIS COOL SPELL MAY BE RELATIVELY SHORT LIVED AS UPPER RIDGING
BUILDS BACK ACROSS THE REGION ALLOWING WARMER TEMPERATURES TO
RETURN NEXT WEEK.
PETR
AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 626 PM CDT MON OCT 12 2026
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- A PERIOD OF LOW-LEVEL WIND SHEAR (LLWS) IS EXPECTED TONIGHT
- A WEAK LAKE BREEZE IS POSSIBLE LATE TOMORROW AFTERNOON
SOUTHWEST WINDS REMAIN BREEZY, PRESENTLY, THOUGH WIND GUSTS
AROUND 20 KNOTS ARE BECOMING MORE SPORADIC. WIND GUSTS ARE
EXPECTED TO CONTINUE TO DIMINISH WITH PREVAILING SOUTHWEST WINDS
AROUND 10 KNOTS THROUGH THE NIGHT. A WESTERLY LOW LEVEL JET
AT 1500 FEET IS PROJECTED TO STRENGTHEN THIS EVENING IN EXCESS
OF 40 KNOTS. THIS WILL RESULT IN A PERIOD OF LLWS AT ALL TAF
TERMINAL SITES. THE JET IS EXPECTED TO WEAKEN TOWARD DAYBREAK
WITH SURFACE WINDS BEGINNING TOMORROW OUT OF THE WEST AND AROUND
10 KNOTS.
CONDITIONS ARE EXPECTED TO BE FAIRLY QUIET AND VFR THROUGH THE
DAY TOMORROW. A LAKE BREEZE IS EXPECTED TO DEVELOP IN THE LATE
AFTERNOON/EARLY EVENING, THOUGH BE FAIRLY LIGHT AS IT
APPROACHES CHICAGO TERMINALS. CLOUD COVER IS EXPECTED TO
INCREASE AFTER 00Z AHEAD OF THE NEXT SYSTEM. CANNOT COMPLETELY
RULE OUT SOME ISOLATED TO WIDELY SCATTERED SHOWERS PRIOR TO 06Z,
BUT WITH GREATER CHANCES AFTER 06Z TOMORROW NIGHT, DECIDED TO
HOLD OFF ADDING IT FOR NOW.
DK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 4 AM CDT TUESDAY FOR THE IL
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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