730
FXUS63 KLOT 160526
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1226 AM CDT FRI OCT 16 2026
KEY MESSAGES
- A FALL STORM SYSTEM WILL MOVE THROUGH THE AREA THROUGH FRIDAY
BRINGING PERIODS OF RAIN SHOWERS AND GUSTY NORTHWESTERLY
WINDS (THE LATTER PRIMARILY ON FRIDAY).
- FROSTY AND NEAR-FREEZING CONDITIONS FAVORED AWAY FROM LAKE
MICHIGAN FRIDAY NIGHT INTO SATURDAY AND AGAIN SATURDAY NIGHT.
- AFTER THE BRIEF PERIOD OF CHILLY WEATHER, THERE WILL BE A
WARMING TREND THIS WEEKEND INTO EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 305 PM CDT THU OCT 15 2026
THROUGH FRIDAY NIGHT:
AN EXPANSIVE FALL STORM SYSTEM CENTERED OVER THE MID-
MISSISSIPPI VALLEY IS LIFTING A WARM FRONT INTO ILLINOIS AND
INDIANA THIS AFTERNOON. DEEP ATMOSPHERIC MOISTURE IS BEING DRAWN
NORTHWARD AHEAD OF THIS SYSTEM, YIELDING PRECIPITABLE WATER
(PWAT) VALUES UP TO 1.75-2.0 INCHES (NEAR RECORD HIGHS) FOR
THIS TIME OF YEAR. THIS MOISTURE WILL SUPPORT NARROW CORRIDORS
OF TORRENTIAL RAIN LATE THIS AFTERNOON AND EVENING, PARTICULARLY
WHERE CONVECTIVE ELEMENTS TRAIN EAST-NORTHEASTWARD. WHILE NOT
EVERYONE WILL EXPERIENCE TORRENTIAL DOWNPOURS, SCATTERED TO
NUMEROUS RAIN SHOWERS ARE EXPECTED AREA-WIDE THROUGH EARLY THIS
EVENING. THE THREAT FOR ISOLATED THUNDERSTORMS REMAINS LOW, BUT
WITH THE PRIMARY MUCAPE RESERVOIR LIFTING ACROSS EAST-CENTRAL
ILLINOIS INTO NORTHERN INDIANA BY EARLY EVENING, ANY
THUNDERSTORM ACTIVITY SHOULD REMAIN PRIMARILY SOUTH OF I-80. A
STRONG STORM OR TWO CANNOT BE RULED OUT THROUGH EARLY EVENING,
BUT THAT THREAT WILL BE CONFINED EVEN FARTHER SOUTH (GENERALLY
SOUTH OF A LINE FROM GIBSON CITY, IL TO REMINGTON, IN), ALIGNING
WELL WITH THE SPC DAY 1 OUTLOOK.
THE PRIMARY LOW-PRESSURE SYSTEM WILL TRACK DIRECTLY OVER
NORTHERN ILLINOIS EARLY THIS EVENING, THEN DEEPEN AS IT SHIFTS
NORTHEAST INTO LOWER MICHIGAN TONIGHT. EXPECT A BRIEF PERIOD OF
LOWER CEILINGS AND REDUCED VISIBILITY FOR A FEW HOURS AS THE LOW
MOVES OVERHEAD. CONDITIONS WILL IMPROVE RAPIDLY LATER TONIGHT
FOLLOWING A SHARP COLD FRONT. IN ITS WAKE, NORTHWEST WINDS WILL
BECOME GUSTY (3035 MPH) OVERNIGHT, WHILE STRONG COLD AIR
ADVECTION DROPS TEMPERATURES INTO THE 40S TO LOW 50S BY EARLY
FRIDAY MORNING. BREEZY CONDITIONS (GUSTS OF 35 TO 40 MPH) WILL
PERSIST THROUGH FRIDAY DUE TO STRONG PRESSURE RISES BEHIND THE
DEPARTING LOW AND AHEAD OF A 1035+ MB SURFACE HIGH BUILDING IN
FROM THE PLAINS. EVEN STRONGER NORTHERLY WINDS (~45 MPH) ARE
PROJECTED OVER SOUTHERN LAKE MICHIGAN FRIDAY AFTERNOON AND
EVENING. ONSHORE FLOW WILL PUSH SOME OF THESE HIGHER WINDS
INLAND ACROSS FAR NORTHERN PORTER COUNTY, INDIANA, WHERE A WIND
ADVISORY IS IN EFFECT FROM 1:00 PM TO 10:00 PM CDT FRIDAY.
MUCH COOLER WEATHER IS EXPECTED FRIDAY, WITH TEMPERATURES
HOVERING IN THE LOW TO MID-50S AS THE COLDEST AIRMASS OF THE
SEASON ARRIVES UNDER A SHARP TROUGH MOVING ACROSS THE WESTERN
GREAT LAKES. STEEPENING LOW- TO MID-LEVEL LAPSE RATES WILL
SUPPORT A DIURNAL INCREASE IN SCATTERED SHOWERS, ESPECIALLY
FRIDAY AFTERNOON. WHILE SHOWERS WILL REMAIN HIT-OR-MISS ACROSS
INTERIOR NORTHERN ILLINOIS, FAVORABLE LAKE-EFFECT CONDITIONS
WILL BRING WIDESPREAD SHOWERS AND POTENTIALLY ISOLATED
THUNDERSTORMS TO SOUTHERN LAKE MICHIGAN AND ADJACENT SHORELINES
FRIDAY AFTERNOON AND EVENING, SUPPORTED BY LAKE-INDUCED
EQUILIBRIUM HEIGHTS EXCEEDING 20,000 FEET.
KJB
FRIDAY NIGHT INTO SATURDAY:
THE PROGRESSIVE PATTERN CONTINUES AS THE SURFACE LOW DEPARTS
AND SURFACE HIGH PRESSURE MOVES TOWARD THE MIDDLE MISSISSIPPI
RIVER VALLEY. LINGERING LAKE-EFFECT CLOUDS AND PERSISTENT COLD
AIR ADVECTION WILL KEEP WINDS SLOWER TO DIMINISH FRIDAY NIGHT
ACROSS EASTERN ILLINOIS AND NORTHWEST INDIANA. FARTHER WEST,
CLEARING SKIES AND LIGHT WINDS NEAR THE APPROACHING SURFACE
RIDGE AXIS ACROSS NORTHWEST ILLINOIS WILL SET THE STAGE FOR A
POTENTIAL FREEZE. IN COLLABORATION WITH WFOS MKX AND DVN, A
FREEZE WATCH WAS ISSUED FOR BOONE, WINNEBAGO, AND OGLE COUNTIES,
WHERE LOWS NEAR 30F ARE EXPECTED EARLY SATURDAY MORNING.
WIDESPREAD FROST IS ALSO LIKELY TO EXTEND FARTHER EAST AND
SOUTH, WHERE FROST ADVISORIES MAY EVENTUALLY BE NEEDED,
POTENTIALLY REACHING AS FAR EAST AS SOME OF THE WESTERN CHICAGO
SUBURBS.
SATURDAY WILL BRING FULL SUNSHINE AND WEAK WINDS AS
HIGH PRESSURE MOVES DIRECTLY OVERHEAD, THOUGH THE CHILLY START
WILL CAP AFTERNOON HIGHS IN THE 50S. SATURDAY NIGHT WILL BE
CHILLY AGAIN, WITH THE COLDEST TEMPERATURES FAVORED EAST OF I-55
BENEATH THE LIGHTEST WINDS NEAR THE HIGH'S CENTER, LIKELY
REQUIRING ADDITIONAL FROST HEADLINES.
SOUTHWESTERLY RETURN FLOW WILL ESTABLISH BY SUNDAY ON THE
BACKSIDE OF THE DEPARTING HIGH, INITIATING A WARMING TREND INTO
EARLY NEXT WEEK.
KJB/BORCHARDT
AVIATION /06Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 1226 PM CDT FRI OCT 16 2026
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- PREVAILING MVFR IS EXPECTED THROUGH MUCH OF TODAY.
- STRONG NORTHWEST WIND GUSTS 25 TO 30 KNOTS OVERNIGHT,
STRENGTHENING IN EXCESS OF 30 KNOTS THIS AFTERNOON.
- WIDELY SCATTERED SHOWERS ARE EXPECTED THIS AFTERNOON, WITH
BEST CHANCES AROUND KGYY AND NORTHWEST INDIANA.
- WIND GUSTS DIMINISH AFTER 00Z WITH IMPROVING/CLEARING SKY
CONDITIONS.
WITH SURFACE LOW PRESSURE MOVING EAST OF CHICAGO, CIGS HAVE
LIFTED SLIGHTLY TO MVFR LEVELS. THESE MVFR CIGS ARE EXPECTED TO
PREVAIL THROUGH MUCH OF THE DAY, THOUGH SLOWLY LIFTING AND
BREAKING UP CLOSER TO 00Z THIS EVENING.
ISOLATED SHOWERS STILL FESTER OVER THE REGION, BUT AS THE LOW
CONTINUES TO EXIT TO THE EAST, DRIER CONDITIONS ARE EXPECTED
THROUGH THE OVERNIGHT. MOST IMPACTFUL WILL BE THE STRENGTHENING
NORTHWEST WIND GUSTS THROUGH THE OVERNIGHT. GUSTS ARE ALREADY
BEING OBSERVED BETWEEN 20 AND 25 KNOTS, AND THAT IS EXPECTED TO
INCREASE TO 25 TO 30 KNOTS THROUGH DAYBREAK. AS DEEPER MIXING
OCCURS DURING THE DAY, GUSTS IN EXCESS OF 30 KNOTS ARE EXPECTED.
ISOLATED GUSTS BETWEEN 35 TO 40 KNOTS ARE POSSIBLE THIS
AFTERNOON, THOUGH THE BETTER CHANCES REMAIN JUST OVER 30 KNOTS.
REDEVELOPING SHOWERS IN THE WAKE OF THE SURFACE LOW IS EXPECTED
THIS AFTERNOON. THERE IS LOWER CONFIDENCE IN COVERAGE, THOUGH
EXPECTED TO BE WIDELY SCATTERED OVER MUCH OF THE AREA, WITH BEST
CHANCES IN NORTHWEST INDIANA AS LAKE MICHIGAN WILL HELP ENHANCE
SHOWER DEVELOPMENT THIS AFTERNOON. NO CHANGES WERE MADE TO THE
PROB30/TEMPO GROUPS, EXCEPT ADJUSTING FOR TIMING EXPECTATIONS.
THE PRESSURE GRADIENT WILL GRADUALLY WEAKEN AFTER 00Z, WINDS
WILL TURN MORE NORTHERLY AND CLOUD COVER WILL BEGIN TO CLEAR.
WIND GUSTS WILL DIMINISH THROUGH THE EVENING WITH A CHANCE THAT
THEY END ALL TOGETHER AFTER MIDNIGHT. FOR NOW, GUSTS WERE
MAINTAINED AT ORD/MDW THROUGH 12Z SATURDAY GIVEN THE LOWER
CONFIDENCE ON EXACT TIMING FOR GUSTS ENDING, BUT WILL BE RE-
EVALUATED AT LATER TAF PACKAGES.
DK
MARINE
ISSUED AT 305 PM CDT THU OCT 15 2026
THE FORECAST REMAINS ON TRACK WITH THE FALL STORM SYSTEM SET TO
IMPACT THE AREA THROUGH FRIDAY.
OVER THE NEXT 18 TO 36 HOURS, THE FIRST FALL STORM SYSTEM OF
THE SEASON WILL MOVE THROUGH THE GREAT LAKES. AS THE LOW LIFTS
INTO NORTHERN IL EARLY THIS EVENING, BREEZY EAST-SOUTHEASTERLY
WINDS WILL CREATE WAVES GENERALLY OF 3 TO 5 FEET ALONG THE
ILLINOIS SHORELINE. WESTERLY WINDS WILL INCREASE IN MAGNITUDE
LATER THIS EVENING ON THE IMMEDIATE BACKSIDE OF THE SYSTEM AND
BEHIND A COLD FRONT WITH FREQUENT GUSTS OF 25 TO 30 KT AND A FEW
GALE FORCE GUSTS TO 35 KT.
FRIDAY AFTERNOON, A SECONDARY COLD FRONT WILL SURGE DOWN LAKE
MICHIGAN LEADING TO A CHANGE IN WIND DIRECTION TO NORTHERLY AND
RAPID INCREASE IN WIND SPEEDS. SUSTAINED WINDS OF 30 TO 35 KT
WITH FREQUENT GUSTS TO 40 KT ARE EXPECTED, WITH LOCALLY HIGHER
GUSTS IN EXCESS OF 45 KT POSSIBLE ON THE WEST SIDE OF LAKE
EFFECT RAIN SHOWERS. THE STRONGEST WIND GUSTS ARE EXPECTED
FRIDAY AFTERNOON AND EVENING BEFORE GRADUALLY TAPERING AFTER
MIDNIGHT EARLY SATURDAY MORNING. A GALE WARNING IS IN EFFECT
FROM 1 PM TO 1 AM FRIDAY NIGHT INTO SATURDAY MORNING.
FINALLY, STRONG LAKE INDUCED INSTABILITY MAY SUPPORT
WATERSPOUTS NEAR LAKE EFFECT SHOWERS FRIDAY AFTERNOON AND
EVENING.
BORCHARDT/KJB
LOT WATCHES/WARNINGS/ADVISORIES
IL...FREEZE WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY MORNING
FOR ILZ003-ILZ004-ILZ008.
IN...WIND ADVISORY FROM 1 PM TO 10 PM CDT FRIDAY FOR INZ002.
LM...SMALL CRAFT ADVISORY UNTIL 1 PM CDT FRIDAY FOR THE IL AND IN
NEARSHORE WATERS.
GALE WARNING FROM 1 PM FRIDAY TO 1 AM CDT SATURDAY FOR THE IL
AND IN NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page