414
FXUS63 KLOT 200557
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1257 AM CDT WED AUG 20 2025
KEY MESSAGES
- DANGEROUS SWIMMING CONDITIONS EXPECTED AT SOUTHERN LAKE
MICHIGAN BEACHES TODAY THROUGH EARLY THURSDAY.
- A CHANCE FOR SPRINKLES OR VERY LIGHT SHOWERS TONIGHT INTO
WEDNESDAY MORNING.
- PATCHY FOG POSSIBLE TONIGHT INTO EARLY WEDNESDAY.
- TEMPERATURES EARLY TO MID NEXT WEEK WILL LIKELY BE AN EARLY
FALL PREVIEW!
DISCUSSION
ISSUED AT 246 PM CDT TUE AUG 19 2025
CONDITIONS ARE QUIET AND RATHER COMFORTABLE OUT THERE THIS
AFTERNOON. THE COLD FRONT THAT MOVED ACROSS LATE LAST NIGHT
DRIVING HEAVY SHOWERS AND THUNDERSTORMS HAS SINCE PUSHED AWAY
FROM OUR CWA INTO CENTRAL IL. ADVECTING IN BEHIND THIS FRONT AND
OVERSPREADING THE AREA IS A THICK STRATOCUMULUS DECK. THE COLD
ADVECTION AND CLOUDY SKIES HAVE KEPT TEMPERATURES LARGELY IN THE
70S SO FAR WITH ONLY A COUPLE OF SITES IN OUR SOUTH REPORTING
80 AS OF 2 PM.
WAVES ARE BUILDING ON SOUTHERN LAKE MICHIGAN THIS AFTERNOON AS
GUSTY NORTHERLY WINDS MOVE OVER THE WATER. THE MICHIGAN CITY
BUOY IS ALREADY REPORTING WAVE HEIGHTS GREATER THAN THREE FEET
AND THEY'RE CLIMBING QUICKLY, WITH A BEACH HAZARDS STATEMENT IN
EFFECT FOR OUR INDIANA COUNTIES. THE HIGH SWIM RISK WILL TAKE
HOLD OF ILLINOIS BEACHES THIS EVENING. THEN EXPECT DANGEROUS
SWIMMING CONDITIONS TO PERSIST THROUGH TOMORROW AND STRETCH INTO
AT LEAST THURSDAY MORNING.
A VERY SUBTLE LOW LEVEL WAVE/BAROCLINIC ZONE WILL BE PUSHING
SOUTH ACROSS THE REGION THIS EVENING INTO TOMORROW. A NUMBER OF
MODEL CAMPS ARE RESOLVING SOUTHWARD-MOVING POCKETS OF VERY LIGHT
RAIN OR SPRINKLES OVERNIGHT WHILE THE WAVE MOVES ACROSS, MOSTLY
OVER AREAS NEAR THE LAKE. BOUNDARY LAYER MOISTURE WILL STRETCH
FARTHER INLAND DURING THE MORNING SPREADING LIGHT PRECIP CHANCES
WEST OF THE CHICAGO METRO FOR THE MORNING HOURS. AS INVERSION
HEIGHTS LIFT, THE SHALLOW UNSTABLE LAYER MAY BECOME SUPPORTIVE
OF TRUE LIGHT SHOWERS FOR A PERIOD DURING THE MORNING BEFORE
DRIER AIR ADVECTS IN FOR THE AFTERNOON.
ADDITIONALLY, THERE IS A GOOD-LOOKING SIGNAL FOR AREAS OF FOG
TO DEVELOP OVERNIGHT WITH PATCHES OF DENSE FOG EVEN POSSIBLE.
THIS IS PRIMARILY A CONCERN ACROSS THE OUTLYING SUBURBS AND
OUTSIDE OF THE CHICAGO METRO. HOW MUCH CLEARING SKIES SEE
TONIGHT WILL ALSO PLAY A ROLE IN THE FOG POTENTIAL, BUT THAT'S
RATHER UNCERTAIN.
A LARGE UPPER HIGH WILL PARK ITSELF OVER THE FOUR CORNERS
REGION FOR THE BACK HALF OF THIS WEEK AND SPREAD A QUIET UPPER
FLOW REGIME OVER THE MIDWEST. THIS SHOULD BRING DRY AND LARGELY
SUNNY CONDITIONS TO THURSDAY AND FRIDAY. TEMPERATURES LEADING UP
TO THIS WEEKEND SHOULD BE SEASONABLY WARM IN THE UPPER 70S AND
LOW 80S. A COLD FRONT LOOKS TO MOVE ACROSS THE REGION FRIDAY
NIGHT AND SATURDAY, BUT A LACK OF FORCING AND INSTABILITY COULD
KEEP PRECIP COVERAGE RATHER LOW. HIGH PRESSURE SHOULD THEN BUILD
IN BEHIND THE FRONT AND KEEP CONDITIONS DRY FOR SUNDAY.
TEMPERATURES ARE EXPECTED TO FALL TO THE COOLER SIDE OF AVERAGE
EARLY NEXT WEEK BEHIND THAT COLD FRONT.
DOOM
AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 1257 AM CDT WED AUG 20 2025
ONLY ITEMS OF NOTE:
- POTENTIAL FOR IFR VSBY IN BR/FOG AT RFD EARLY THIS MORNING.
- MVFR CIGS DEVELOPING IN THE PRE-DAWN HOURS TODAY AND
PERSISTING THROUGH EARLY TO MID AFTERNOON NEAR THE LAKE.
THE THEME OF MUCH QUIETER FLYING CONDITIONS WILL CONTINUE
THROUGH THE NEXT SEVERAL TAF CYCLES. IN THE NEAR TERM OF THE
CURRENT TAF PERIOD, PATCHY DENSE FOG HAS DEVELOPED AT RPJ WHERE
SKIES WERE MOSTLY CLEAR. THERE MAY BE ENOUGH CLOUDS TO PREVENT
LIFR VSBY AT RFD, THOUGH A PERIOD OF AT LEAST OCCASIONAL IFR
VSBY APPEARS LIKELY ENOUGH TO MAINTAIN TEMPO MENTION. FOR DPA,
THE MORE LIKELY SCENARIO LOOKS TO BE TEMPO MVFR VSBY.
MVFR CIGS WILL STREAM SOUTH IN THE PRE-DAWN THROUGH MID MORNING
HOURS, WITH LAKE INFLUENCE KEEPING THEM IN PLACE A BIT LONGER AT
THE NEAR-LAKE TERMINALS. NORTH-NORTHEAST WINDS WILL GUST TO
NEAR/AROUND 20 KT AT TIMES FROM THIS MORNING THROUGH THE MID-
LATE EVENING, FOLLOWED BY PREVAILING 5-10 KT SPEEDS THEREAFTER.
CASTRO
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page