504
FXUS63 KLOT 210609
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
109 AM CDT TUE OCT 21 2025
KEY MESSAGES
- PERIOD OF RAIN EXPECTED MID-LATE EVENING TONIGHT, THEN SOME
ISOLATED TO SCATTERED SHOWERS EXPECTED TUESDAY AFTERNOON/EARLY
EVENING.
- STRONG WEST WINDS, GUSTING BETWEEN 30-40 MPH, ARE EXPECTED
TUESDAY AFTERNOON WITH A FEW PEAK GUSTS TO AROUND 45 MPH
POSSIBLE.
- SEASONABLY COOL TEMPERATURES ARE EXPECTED THE REMAINDER OF THE
UPCOMING WORK WEEK.
DISCUSSION
ISSUED AT 237 PM CDT MON OCT 20 2025
THROUGH TUESDAY NIGHT:
UPPER TROUGH OVER THE NORTHERN GREAT PLAINS AND SOUTHERN
CANADIAN PRAIRIES IS DIGGING SOUTHEASTWARD EARLY THIS AFTERNOON.
WATER VAPOR IMAGERY SHOWS SEVERAL VORTICITY MAXIMUMS EMBEDDED
WITHIN THE LARGER TROUGH. AT THE SURFACE, THERE IS A 997 MB SFC
LOW OVER NORTHERN MN WITH A COLD FRONT TRAILING SOUTH FROM THE
LOW ACROSS CENTRAL IA. GUIDANCE IS IN GOOD AGREEMENT IN DRIVING
THIS UPPER TROUGH INTO THE WESTERN GREAT LAKES BY TUESDAY
MORNING, CLOSING OFFS A DEEPENING MID-UPPER LEVEL LOW WITH
MULTIPLE VORTICITY MAXIMUMS PIVOTING AROUND THE MID-UPPER LEVEL
CYCLONE AS IT MOVES SLOWLY EASTWARD ACROSS THE GREAT LAKES
THROUGH MIDWEEK.
ALREADY SEEING STRONG AND GUSTY SOUTHERLY WINDS TODAY IN
RESPONSE TO THE TIGHTENING PRESSURE GRADIENT ASSOCIATED WITH THE
SFC LOW OVER MN. THE MAGNITUDE OF THE WINDS/GUSTINESS SHOULD
EASE A BIT AFTER SUNSET. THE COLD FRONT WILL MOVE QUICKLY ACROSS
THE AREA TONIGHT, LIKELY ACCOMPANIED BY A BAND OF SOME RAIN,
ESPECIALLY NORTH OF I-80. THE WINDOW OF RAIN SHOULD BE RATHER
SHORT, LIKELY LASTING ONLY AN HOUR OR SO IN ANY ONE GIVEN AREA.
WINDS WILL SHIFT TO WESTERLY IN THE WAKE OF THE FRONT TONIGHT,
BUT SPEEDS AND GUSTS WILL REALLY BEGIN TO RAMP UP AFTER SUNRISE
TUESDAY. DEEPLY MIXED BOUNDARY SHOULD ALLOW FOR FAIRLY FREQUENT
GUSTS OF 30-40 MPH BY LATE MORNING AND ESPECIALLY DURING THE
AFTERNOON. THERE WILL PROBABLY BE SOME SPORADIC GUSTS THAT TAG
WIND ADVISORY CRITERIA (45 MPH GUSTS), BUT CURRENT THINKING IS
THAT ANY 45+ MPH GUSTS WILL BE MUCH MORE THE EXCEPTION THAN THE
RULE, SO NOT PLANNING A WIND ADVISORY AT THIS TIME.
MOST GUIDANCE DEPICTS ONE OF THE MORE VIGOROUS VORTS PIVOTING
AROUND THE UPPER LOW MOVING ACROSS OUR CWA DURING THE MORNING
HOURS TUESDAY. BY THE TIME THE BOUNDARY LAYER BECOMES MORE
DIURNALLY UNSTABLE, THE BETTER FORCING WITH THIS VORT SHOULD BE
STARTING TO PUSH EAST OF OUR AREA INTO MI AND EASTERN IN. THIS
WOULD SUGGEST THE BETTER DIURNAL, AFTERNOON COLD CORE SHOWER
CHANCES MAY END UP BEING JUST EAST OF OUR CWA AS INVERSION
HEIGHTS LOWER SOME IN WAKE OF THIS VORT. FORECAST SOUNDINGS
STILL DEPICT CONVECTIVE CLOUD DEPTHS OF 5-6KFT, SO CERTAINLY
PLAUSIBLE THAT THERE WILL BE SOME ISOLATED TO SCATTERED LIGHTER
SHOWERS AROUND IN THE AFTERNOON, PARTICULARLY NORTHERN CWA
CLOSER TO THE CORE OF THE COLDER TEMPS ALOFT. SHOWER CHANCES
COULD LINGER INTO THE EARLY EVENING HOURS TUESDAY, BUT SHOULD BE
ON THE DECREASE AFTER SUNSET TUESDAY.
- IZZI
WEDNESDAY THROUGH MONDAY:
THE STACKED DEEP UPPER AND SURFACE LOWS ARE PROGGED TO DRIFT
EAST TO THE LAKE HURON/GEORGIAN BAY REGION ON WEDNESDAY, WITH OUR
AREA REMAINING IN PERSISTENT BLUSTERY 15-20 MPH (GUSTS 25-30 MPH)
WEST-NORTHWEST LOW-LEVEL COLD ADVECTION FLOW. THIS BRISK WEST-
NORTHWEST FLOW REGIME WILL CERTAINLY KEEP ROBUST LAKE EFFECT
RAIN SHOWERS GOING INTO THURSDAY. HOWEVER, THE ~280-300 DEG WIND
DIRECTION WILL KEEP THE FOCUS PRIMARILY EAST/NORTHEAST OF PORTER
COUNTY INDIANA. TEMPERATURES AGAIN LOOK TO BE LIMITED TO THE LOW-
MID 50S, WITH 30S LIKELY WEDNESDAY NIGHT ESPECIALLY AWAY FROM THE
HEART OF THE CHICAGO AREA. AT THIS TIME, THERE APPEARS TO BE
ENOUGH OF A SURFACE WIND TO PREVENT WIDESPREAD FROST CONDITIONS,
THOUGH CLEARING SKIES OVERNIGHT COULD SUPPORT STRONGER DECOUPLING
THAN IS CURRENTLY DEPICTED AND WILL HAVE TO BE MONITORED. WITH
THIS IN MIND, ADDED IN PATCHY FROST MENTION INTO THURSDAY MORNING
FOR AREAS PRIMARILY WEST OF THE FOX RIVER VALLEY.
ENSEMBLE GUIDANCE IS IN REASONABLE AGREEMENT IN GRADUALLY
SHIFTING THE LONG-WAVE UPPER TROUGH OFF TO THE EAST OF THE
REGION THURSDAY INTO FRIDAY, WITH AN ELONGATED NORTHWEST-
SOUTHEAST ORIENTED SURFACE HIGH PRESSURE RIDGE SPREADING ACROSS
THE AREA TOWARD FRIDAY MORNING. LIGHT WINDS AND CLEAR SKIES
WITH THE SURFACE RIDGE OVERHEAD WOULD POTENTIALLY SUPPORT A MORE
WIDESPREAD FROST/FREEZE THREAT (AND ASSOCIATED HEADLINES) LATE
THURSDAY NIGHT/EARLY FRIDAY MORNING. AS SUCH, INTRODUCED AREAS OF
FROST OUTSIDE THE HEART OF THE CHICAGO URBAN HEAT ISLAND AND AWAY
FROM THE LAKE IN NORTHWEST INDIANA.
SOME MODEST MODERATION IN TEMPS IS THEN INDICATED FRIDAY INTO
THE WEEKEND, AS ENSEMBLES SHIFT THE SURFACE RIDGE OFF TO OUR
EAST, AND GENERALLY INDICATE SOME SEMBLANCE OF A SHORT WAVE
TRACKING ACROSS THE CENTRAL/SOUTHERN PLAINS. THIS WAVE IS
PROGGED TO EVENTUALLY GET KICKED INTO THE MIDWEST/GREAT LAKES
REGION BY ANOTHER UPSTREAM LONG-WAVE TROUGH MOVING ONTO THE WEST
COAST. MOST GLOBAL ENSEMBLES INCREASE PRECIP CHANCES INTO THE
REGION IN ASSOCIATION WITH THIS SCENARIO, THOUGH CONFIDENCE IN
PLACEMENT AND EVOLUTION OF THE LEADING PLAINS WAVE IS FAIRLY
LOW AT THIS DISTANCE. BLENDED NBM POPS IN THE 20-40 PERCENT
RANGE BY SATURDAY INTO SUNDAY APPEAR REASONABLE FOR NOW. ANOTHER
TROUGH MAY EJECT INTO THE REGION EARLY NEXT WORK WEEK, WHICH COULD
BRING RAIN (AND EVENTUALLY EVEN SOME THUNDER) CHANCES BACK AS
EARLY AS MONDAY AFTERNOON AND EVENING. AS IS TYPICAL AT THAT RANGE,
ENSEMBLE VARIANCE IS QUITE LARGE IN THE TIMING AND EVOLUTION OF
THAT POSSIBLE SYNOPTIC SYSTEM.
CASTRO/RATZER
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 237 PM CDT MON OCT 20 2025
HAVE ISSUED A GALE WARNING FOR THIS EVENING AS STRENGTHENING LOW
LEVEL FLOW AND NEUTRAL TO SLIGHTLY UNSTABLE CONDITIONS SHOULD
ALLOW FOR SOME FAIRLY REGULAR SOUTHERLY GALE FORCE GUSTS THIS
EVENING. SHOULD SEE A BREAK IN THE GALES LATE TONIGHT INTO EARLY
TUESDAY MORNING AS WIND SHIFT TO THE WEST BEHIND COLD FRONT. THE
WINDS ARE THEN LIKELY TO RAMP BACK UP TO 35-40KT WESTERLY GUSTS
TUESDAY AFTERNOON, CONTINUING TUESDAY NIGHT, AND LIKELY INTO AT
LEAST EARLY WEDNESDAY MORNING. MODEL GUIDANCE DOES DEPICT SOME
EASING OF THE WINDS TUESDAY NIGHT, 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. MAINTAINED 35KT GALES TUESDAY NIGHT,
BUT QUITE POSSIBLE THIS COULD BE TOO CONSERVATIVE, PARTICULARLY
FOR THE INDIANA WATERS. HAVE ISSUED A SECOND GALE WARNING FOR THIS
TUESDAY AFTERNOON THROUGH EARLY WEDNESDAY MORNING PERIOD.
- IZZI
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.
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