533
FXUS63 KLOT 210832
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
332 AM CDT TUE OCT 21 2025
KEY MESSAGES
- STRONG WEST WINDS, GUSTING BETWEEN 30-40 MPH, DEVELOP THIS
AFTERNOON AND EVENING WITH A FEW PEAK GUSTS TO AROUND 45 MPH.
- SCATTERED SHOWERS DEVELOP BY THIS AFTERNOON AND PERSIST THIS
EVENING.
- SEASONABLY COOL TEMPERATURES ARE EXPECTED THE REMAINDER OF THE
WORK WEEK.
DISCUSSION
ISSUED AT 332 AM CDT TUE OCT 21 2025
THROUGH WEDNESDAY:
A DEEP UPPER-LEVEL TROUGH WAS EVIDENT IN GOES VAPOR IMAGERY
OVER THE UPPER MIDWEST EARLY THIS MORNING, WITH AN EMBEDDED
CLOSED UPPER LOW OVER NORTHWEST MN. SEVERAL INDIVIDUAL MID-LEVEL
VORT MAXIMA WERE NOTED WRAPPING CYCLONICALLY AROUND THE
SOUTHERN PERIPHERY OF THE MAIN CIRCULATION, WITH AN INITIAL
STRONG WAVE CURRENTLY EXITING THE FORECAST AREA TO THE EAST. A
SECOND VORT WAS PROPAGATING SOUTHEAST FROM THE EASTERN DAKOTAS,
AND WILL APPROACH THE AREA LATER THIS MORNING. YET ANOTHER, ON
THE WESTERN EDGE OF THE UPPER LOW, IS PROGGED TO TRACK ACROSS
THE FORECAST AREA LATE THIS AFTERNOON AND EVENING. THE
COMBINATION OF FORCING WITH THESE INDIVIDUAL VORTS, AND OUR
POSITION ALONG THE SOUTHERN EDGE OF A SEASONABLY-COLD MID-LEVEL
COLD POOL (NEAR -28C AT 500 MB) WILL SUPPORT THE DEVELOPMENT OF
STEEP LOW TO MID-LEVEL LAPSE RATES WHICH WILL SUPPORT BOTH
STRONG, GUSTY SURFACE WINDS AND THE DEVELOPMENT OF SCATTERED
CONVECTIVE SHOWERS, MOST NOTABLY NORTH OF I-80 THIS AFTERNOON
AND EVENING.
SUSTAINED WESTERLY WINDS OF 20-25 MPH AND GUSTS 30-40 MPH (A
FEW AS HIGH AS 45 MPH) ARE LIKELY BY AFTERNOON AND WILL PERSIST
INTO EARLY THIS EVENING. BLUSTERY WINDS, SCATTERED SHOWERS AND
TEMPERATURES RANGING FROM THE MID-50S NORTH TO THE UPPER 50S
SOUTH WILL MAKE FOR A RAW FEEL TO THE DAY BY THIS AFTERNOON, AND
TEMPS MAY FALL SLOWLY IN THE AFTERNOON WITH INCREASING CLOUD
COVER AND PERSISTENT COLD ADVECTION. SHOWER COVERAGE (WHICH
SHOULD BE GREATEST NORTH OF I-80 IN GENERAL) IS EXPECTED TO
DECREASE LATE THIS EVENING, AS THE THIRD VORT PASSES AND MOVES
EAST OF THE REGION. WINDS ARE ALSO EXPECTED TO EASE LATE THIS
EVENING, BUT WILL REMAIN BLUSTERY WITH GUSTS AROUND 30 MPH AT
TIMES. WINDS AND CLOUD COVER WILL HELP KEEP OVERNIGHT TEMPS FROM
GETTING TOO COLD HOWEVER, WITH OVERNIGHT LOWS MAINLY IN THE
LOWER 40S EXPECTED IN MOST AREAS.
THE STACKED UPPER LOW AND ASSOCIATED OCCLUDED SURFACE LOW ARE
EXPECTED TO SLOWLY DRIFT EAST ALONG THE NORTH SHORE OF GEORGIAN
BAY ON WEDNESDAY, WHILE GRADUALLY FILLING. DEEP NORTHWEST FLOW
WILL PERSIST ACROSS THE REGION, THOUGH WITH SLIGHTLY LIGHTER
SURFACE WINDS GUSTING AROUND 30 MPH. CLOUDS ARE EXPECTED TO
LINGER NORTH OF I-80, THOUGH GENERALLY DRY WEATHER IS EXPECTED
OUTSIDE OF A FEW LAKE EFFECT RAIN SHOWERS WHICH MAY CLIP
NORTHEASTERN PORTER COUNTY AT TIMES IN NORTHWEST IN. HIGH TEMPS
WEDNESDAY ARE EXPECTED TO RANGE FROM THE LOWER 50S NORTH, TO THE
MID-50S SOUTH OF I-80.
RATZER
WEDNESDAY NIGHT THROUGH MONDAY:
THE CONTINUED PRESENCE OF A STACKED UPPER-LEVEL LOW/MEAN LONGWAVE
TROUGH AND ITS ASSOCIATED COLD POOL OF AIR ALOFT OVER THE GREAT
LAKES WILL ALLOW FOR LAKE EFFECT RAIN SHOWERS TO PERSIST OVER
AND DOWNWIND OF LAKE MICHIGAN WEDNESDAY NIGHT INTO THURSDAY. THE
PREVAILING WESTERLY TO WEST-NORTHWESTERLY WIND DIRECTION OVER
THE LAKE SHOULD KEEP MOST OR ALL OF THIS SHOWER ACTIVITY TO THE
EAST/NORTHEAST OF OUR FORECAST AREA, BUT AT THIS TIME, STILL
COULDN'T RULE OUT THAT A FEW SHOWERS SNEAK INTO NORTHERN PORTER
COUNTY WEDNESDAY NIGHT INTO THURSDAY MORNING. AWAY FROM LAKE
MICHIGAN, CLEAR SKIES WILL LARGELY BE PREVALENT WEDNESDAY NIGHT
INTO THURSDAY MORNING. WITH MODEST COLD AIR ADVECTION OFF OF
WEST-NORTHWESTERLY WINDS EXPECTED TO STILL BE ONGOING,
TEMPERATURES WILL FALL INTO THE 30S AWAY FROM THE HEART OF THE
CHICAGO URBAN HEAT ISLAND AND WHERE ANY STRATOCUMULUS IS
PRESENT. THERE WILL THUS BE A THREAT FOR FROST IN THESE AREAS,
THOUGH THE AFOREMENTIONED WINDS MAY REMAIN JUST STRONG ENOUGH TO
PRECLUDE A MORE WIDESPREAD FROST FROM MATERIALIZING.
THURSDAY INTO FRIDAY, THE UPPER LOW/LONGWAVE TROUGH WILL
PROGRESS EASTWARD, AND A LOW-AMPLITUDE RIDGE WILL TAKE ITS
PLACE. SURFACE HIGH PRESSURE BENEATH THIS UPPER-LEVEL RIDGE WILL
ALLOW FOR DRY CONDITIONS TO PERSIST INTO FRIDAY ACROSS THE
AREA. DESPITE THE EXPECTED AMPLE SUNSHINE, HIGH TEMPERATURES ON
THURSDAY AND FRIDAY SHOULD END UP BEING NEAR TO SLIGHTLY BELOW
MID/LATE OCTOBER CLIMATOLOGICAL NORMALS. WINDS THURSDAY NIGHT
INTO FRIDAY MORNING WILL BE LIGHT/CALM AS A RESULT OF THE
SURFACE HIGH PRESSURE'S INFLUENCE, AND WITH THE CONTINUED CLEAR
SKIES, CONDITIONS WILL BE MORE OPTIMAL FOR RADIATIONAL COOLING
AND FROST DEVELOPMENT COMPARED TO THE PREVIOUS NIGHT. THE LATEST
LOW TEMPERATURES OFFERED UP BY THE NBM WOULD ACTUALLY SUPPORT A
FREEZE OCCURRING ACROSS A GOOD CHUNK OF NORTHERN ILLINOIS
OUTSIDE OF THE CHICAGO METRO, THOUGH IT'S WORTH NOTING THAT THE
NBM'S LOWS FOR FRIDAY MORNING ARE ON THE LOWER END OF THE
SPECTRUM OF AVAILABLE FORECAST GUIDANCE AND ARE A FEW DEGREES
LOWER THAN THE ENSEMBLE MEANS FROM THE 00Z RUNS OF THE EPS AND
GEFS. THUS, A FREEZE OCCURRING IN OUR FORECAST AREA ON FRIDAY
MORNING IS STILL FAR FROM A LOCK, BUT THE ODDS OF A WIDESPREAD
FROST BEING OBSERVED IN AT LEAST PART OF OUR FORECAST AREA
APPEAR TO BE PRETTY GOOD AT THIS TIME, ALL THINGS CONSIDERED.
GOING INTO THE WEEKEND, OUR CHANCES FOR SEEING PRECIPITATION
SHOULD INCREASE AS A NORTHERN STREAM UPPER-LEVEL SHORTWAVE AND
AN (AT TIMES) CLOSED-OFF UPPER-LEVEL DISTURBANCE FARTHER TO
SOUTH BOTH ATTEMPT TO MAKE INROADS INTO THE REGION. ENSEMBLE
VARIANCE FOR THE EXACT TRACK AND EVOLUTION OF BOTH OF THESE
DISTURBANCES REMAINS SOMEWHAT LARGE AT THIS TIME, SO BROAD-
BRUSHED SLIGHT CHANCE AND LOWER-END CHANCE POPS AS DELIVERED
BY THE NBM FOR THE WEEKEND APPEAR TO ADEQUATELY CONVEY THE
EXISTING UNCERTAINTY. A MORE POTENT TROUGH WILL LIKELY EJECT
INTO THE CENTRAL CONUS EARLY NEXT WEEK. THIS COULD BRING A
BETTER OPPORTUNITY FOR MORE WIDESPREAD RAINFALL (AND POSSIBLY
EVEN SOME THUNDERSTORMS) INTO THE AREA, BUT AGAIN, ENSEMBLE
VARIANCE IS STILL UNSURPRISINGLY LARGE REGARDING THIS TROUGH'S
EVOLUTION AT THIS VANTAGE POINT.
OGOREK
AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 108 AM CDT TUE OCT 21 2025
KEY MESSAGES:
- STRONG WESTERLY WINDS WITH GUSTS IN EXCESS OF 30 KTS EXPECTED
THIS AFTERNOON INTO TONIGHT.
- PERIOD OF SHOWERS EXPECTED THIS AFTERNOON INTO THIS EVENING.
- MVFR CEILINGS POSSIBLE LATE THIS AFTERNOON INTO TONIGHT.
WHILE THERE SHOULD BE A RELATIVE LULL IN GUSTINESS THROUGH THE
EARLY MORNING, WESTERLY WIND GUSTS IN EXCESS OF 20 KTS SHOULD
RESUME BY AROUND MID-MORNING. WINDS WILL THEN STRENGTHEN FURTHER
DURING THE AFTERNOON, WHEN GUSTS IN EXCESS OF 30 KTS (AND
POSSIBLY EVEN APPROACHING 40 KTS AT TIMES) ARE LIKELY TO BE
OBSERVED. WESTERLY GUSTS TO AROUND 30 KTS ARE THEN LIKELY TO
CONTINUE WELL BEYOND SUNSET.
DISTURBANCES EMBEDDED WITHIN A LARGE UPPER-LEVEL LOW PRESSURE
AREA OVER THE GREAT LAKES WILL LIKELY CAUSE A FLARE-UP OF
SCATTERED TO NUMEROUS SHOWERS OVER THE AREA THIS AFTERNOON. A
FEW OF THESE SHOWERS COULD BRIEFLY KNOCK VISIBILITIES DOWN TO
MVFR LEVELS BEFORE SHOWER COVERAGE WANES THIS EVENING.
LASTLY, MVFR CEILINGS ARE POSSIBLE AS EARLY AS THE MID-AFTERNOON,
BUT ARE MORE LIKELY TO BE OBSERVED AFTER SUNSET. HOWEVER, SOME
UNCERTAINTY REMAINS OVER HOW FAR SOUTH THE SOUTHERN TERMINUS OF
THE MVFR CLOUD DECK WILL GET, AND IT REMAINS POSSIBLE THAT VFR
CONDITIONS END UP LARGELY PREVAILING TONIGHT AT SOME OF OUR TAF
SITES.
OGOREK
MARINE
ISSUED AT 332 AM CDT TUE OCT 21 2025
BRIEF GALES ASSOCIATED WITH LAST EVENING'S COLD FRONT HAVE EASED FOR
THE TIME BEING, AND THE CURRENT GALE WARNING HAS BEEN ALLOWED TO
EXPIRE AS OF 3 AM CDT. A SMALL CRAFT ADVISORY REMAINS IN EFFECT THIS
MORNING HOWEVER, DUE TO LINGERING WAVE ACTION AND 25-30 KT WESTERLY
WINDS WILL BEGIN TO RAMP UP AGAIN MID-LATE MORNING.
GALE WARNINGS GO BACK INTO EFFECT AT NOON TODAY, AND WILL REMAIN IN
EFFECT INTO AT LEAST EARLY WEDNESDAY MORNING AS WESTERLY WINDS
CONTINUE TO INCREASE TO 35-40 KT THIS AFTERNOON. MODEL GUIDANCE DOES
DEPICT SOME EASING OF THE WINDS LATE TONIGHT, BUT THIS CORRESPONDS
TO THE TIME OF A SIGNIFICANT INCREASE IN MARINE BOUNDARY LAYER
INSTABILITY. THIS OFTEN RESULTS IN WINDS OVER PERFORMING WHAT MODEL
GUIDANCE WOULD SUGGEST. HAVE MAINTAINED 35 KT GALES FOR LATER
TONIGHT, BUT IT IS POSSIBLE THIS COULD BE TOO CONSERVATIVE,
PARTICULARLY FOR THE LONGER OVER-WATER FETCH IN THE INDIANA WATERS.
IZZI/RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...GALE WARNING UNTIL 3 AM CDT EARLY THIS MORNING FOR THE IL AND
IN NEARSHORE WATERS.
GALE WARNING FROM NOON TODAY TO 9 AM CDT WEDNESDAY FOR THE IL
AND IN NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL NOON CDT TODAY FOR THE IL AND IN
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page