493
FXUS63 KLOT 201940
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
240 PM CDT WED AUG 20 2025
KEY MESSAGES
- CHOPPY WAVES AND DANGEROUS RIP CURRENTS WILL CONTINUE AT LAKE
MICHIGAN BEACHES THROUGH THURSDAY MORNING.
- PATCHY DENSE FOG MAY DEVELOP OVERNIGHT.
- OTHERWISE, LITTLE TO NO IMPACTFUL WEATHER IS EXPECTED THROUGH
THE UPCOMING WEEKEND AND EARLY NEXT WEEK. AN EARLY FALL
TEMPERATURE PREVIEW REMAINS IN STORE SUNDAY-TUESDAY.
DISCUSSION
ISSUED AT 240 PM CDT WED AUG 20 2025
THE EARLY PART OF THIS AFTERNOON SEES TEMPERATURES IN THE 70S
BENEATH MOSTLY CLOUDY CONDITIONS. DENSE CUMULUS COVERAGE
OVERHEAD IS GRADUALLY BEGINNING TO THIN OUT HERE AS DRIER LOW-
MID LEVEL AIR ADVECTS IN FROM THE NORTH. MOSTLY CLEAR SKIES ARE
FORECAST OVERNIGHT WHICH WILL ALLOW TEMPERATURES TO FALL INTO
THE LOWER AND MIDDLE 60S AND SET THE STAGE FOR SOME POTENTIAL
PATCHY FOG, PRIMARILY OUTSIDE OF COOK COUNTY. FOG COULD BE DENSE
IN SPOTS AND STRETCH INTO THE MORNING COMMUTE, SO AT LEAST
ISOLATED INSTANCES OF HAZARDOUS TRAVEL WILL BE POSSIBLE THROUGH
EARLY TOMORROW.
THE HIGH SWIM RISK CONTINUES AT ALL IL AND IN LAKE MICHIGAN
BEACHES FOR THE REST OF TODAY FOR HIGH WAVES AND DANGEROUS
CURRENTS. BUOYS ARE LARGELY REPORTING 3 TO 6 FOOT WAVES AROUND
OUR SHORELINE; THE MICHIGAN CITY BUOY WAS PREVIOUSLY REPORTING
WAVES TO 7 FEET THIS MORNING. SWIMMING CONDITIONS WILL REMAIN
HAZARDOUS THROUGH TOMORROW MORNING BEFORE EASING FOR THE
AFTERNOON AND EVENING.
UPPER HIGH PRESSURE IS BROADENING OVER THE SOUTHWEST CONUS
TODAY AND WILL REMAIN INTO THE END OF THE WEEK. BENEATH ITS
LEEWARD SIDE, BROAD SURFACE HIGH PRESSURE WILL OVERSPREAD THE
GREAT LAKES REGION. THIS WILL BRING QUIET WEATHER TO TOMORROW
AND FRIDAY WITH MOSTLY SUNNY SKIES AND SEASONABLE HIGHS IN THE
UPPER 70S AND LOWER 80S. ONSHORE WINDS SHOULD KEEP AREAS AROUND
THE LAKE STUCK IN THE LOWER 70S TOMORROW.
AN UPPER TROUGH WILL OVERCOME THE HIGH LATER THIS WEEK AND
SWING ITS BASE ACROSS THE NORTHERN PLAINS AND THEN INTO THE
UPPER MIDWEST ON SATURDAY. THE SURFACE RESPONSE WILL BE A COLD
FRONT APPROACHING THE AREA FROM THE NORTHWEST LATE FRIDAY AND
MOVING ACROSS THE CWA SOMETIME DURING THE DAY ON SATURDAY.
MEDIUM-RANGE GUIDANCE CONTINUES TO BE PESSIMISTIC WITH PRECIP
CHANCES AROUND THE FRONT. IT APPEARS THAT THE MUCH BETTER LAYER
MOISTURE WILL BE POOLED JUST AHEAD OF THE FRONT WHILE THE MORE
APPRECIABLE FORCING AND COOLER MID-LEVEL AIR (STEEPER LAPSE
RATES) WILL LAG BEHIND WITH PROFILES QUICKLY DRYING OUT
IMMEDIATELY BEHIND THE BOUNDARY. THERE IS ALSO UNCERTAINTY WITH
THE TIMING OF THE FRONTAL PASSAGE, WHICH LOOKS TO PLAY A BIG
ROLE. IN EARLIER SOLUTIONS LIKE THE EURO, THERE ISN'T MUCH
OPPORTUNITY TO DESTABILIZE AHEAD OF THE FRONT AND PRECIP
COVERAGE MAY BE TIGHTLY CONFINED TO THE BOUNDARY. BUT IF THE
FRONT CAN HOLD OFF UNTIL LATER IN THE AFTERNOON TO PUSH ACROSS,
BOUNDARY LAYER DESTABILIZATION SHOULD INTERACT WITH THE HIGHER
MOISTURE AHEAD OF THE FRONT AND PRESENT A BETTER OPPORTUNITY FOR
SCATTERED CONVECTION. THE NBM CONTINUES TO RESOLVE ONLY SLIGHT
CHANCE OR DRY POPS DURING THE DAYTIME, BUT JUST ABOUT EVERY
PIECE OF DETERMINISTIC GUIDANCE THAT LOOKS BEYOND SATURDAY
RESOLVES MEASURABLE QPF AROUND THE CWA BY THE END OF THE DAY,
AND A BIG MAJORITY OF ENSEMBLE MEMBERS FROM THE EPS AND GEFS
RESOLVE PRECIP AS WELL. SO WHILE COVERAGE AND INTENSITY REMAIN
RATHER UNCERTAIN, AT LEAST SOME PRECIP IS LOOKING LIKELY AROUND
MOST OF THE AREA ON SATURDAY. ACCORDINGLY, COORDINATED WITH
NEIGHBORING OFFICES TO BOOST POPS SLIGHTLY FROM THE NBMS
SOLUTION TO INCLUDE CHANCES FOR RAIN AND STORMS DURING THE DAY.
THE BASE OF THE UPPER TROUGH WILL DIP SOUTH INTO OUR GENERAL
REGION AND REMAIN THERE FOR A FEW DAYS NEXT WEEK. DEEP COLD
ADVECTION WILL RESULT AND BRING AN EARLY FALL-LIKE FEEL TO THE
EARLY PART OF NEXT WEEK. HIGHS SUNDAY THROUGH TUESDAY ARE
FORECAST IN THE UPPER 60S AND LOWER 70S WITH TEMPERATURES
LOOKING TO MODERATE CLOSER TO NORMAL TOWARD THE END OF THE WEEK.
DOOM
AVIATION /18Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 1224 PM CDT WED AUG 20 2025
FORECAST CONCERNS FOR THE TERMINALS...
- LINGERING MVFR CEILINGS THROUGH 19-20Z.
- 20% CHANCE FOR PATCHY FOG LATE TONIGHT MAINLY IN NORTHWEST IL.
MVFR CEILINGS CONTINUE TO OOZE INLAND OFF OF LAKE MICHIGAN AS
OFF THIS WRITING, BUT SATELLITE TRENDS DO SHOW THE CEILINGS
STARTING TO ERODE. THEREFORE, SUSPECT MVFR CONDITIONS WILL LIFT
TO VFR BY 19-20Z AT THE LATEST WITH VFR CONDITIONS EXPECTED
THEREAFTER. AS CLOUDS LIFT, WINDS WILL ALSO INCREASE WITH GUSTS
IN THE LOWER 20 KT RANGE EXPECTED AT THE CHICAGO TERMINALS AND
GYY WITH 10-12 KT WINDS ELSEWHERE. GUSTS WILL SUBSIDE THIS
EVENING WITH EASTERLY 5-10 KT WINDS FOR THE REST OF THE PERIOD.
FINALLY, THERE IS A LOW CHANCE (AROUND 20%) FOR PATCHY FOG TO
DEVELOP MAINLY ACROSS NORTHWEST IL LATE TONIGHT INTO EARLY
THURSDAY MORNING. GIVEN THAT WINDS JUST ABOVE THE SURFACE LOOK
TO REMAIN ELEVATED, CONFIDENCE ON FOG COVERAGE IS LOW AND THUS
HAVE FORGONE A FORMAL TAF MENTION AT THIS TIME.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...BEACH HAZARDS STATEMENT THROUGH THURSDAY MORNING FOR ILZ006-
ILZ103-ILZ104.
IN...BEACH HAZARDS STATEMENT THROUGH THURSDAY MORNING FOR INZ001-
INZ002.
LM...SMALL CRAFT ADVISORY UNTIL 4 AM CDT THURSDAY FOR THE IL AND IN
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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