781
FXUS63 KLOT 180700
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
200 AM CDT FRI SEP 18 2026
KEY MESSAGES
- PERIODS OF HEAVY RAIN AND SCATTERED THUNDERSTORMS LATE TONIGHT
THROUGH SUNDAY NIGHT. LOCALIZED FLASH FLOODING WILL BE
POSSIBLE WHERE THE HEAVIEST RAINS OCCUR OVER THE SAME AREAS.
- BELOW NORMAL TEMPS EARLY NEXT WEEK THEN DRY WEATHER EXPECTED
MID/LATE NEXT WEEK.
DISCUSSION
ISSUED AT 200 AM CDT FRI SEP 18 2026
THE PRIMARY FORECAST FOCUS AND CHALLENGE REMAINS TIMING AND
LOCATION OF PERIODS OF HEAVY RAIN THROUGH SUNDAY.
LOW CLOUDS CONTINUE TO SLOWLY SCATTER OUT ACROSS SOUTHERN LAKE
MICHIGAN AND INTO FAR NORTHEAST IL EARLY THIS MORNING. THIS
TREND IS EXPECTED TO CONTINUE INLAND THIS MORNING THOUGH THERE
WILL LIKELY BE MID LEVEL CLOUD COVER LATER TODAY. NET RESULT
SHOULD BE AT LEAST SOME PEAKS OF SUNSHINE TODAY. A WEAK WAVE MAY
BRING A FEW SHOWERS TO WESTERN AND NORTHWEST IL TODAY, BUT MUCH
OF THE AREA IS EXPECTED TO REMAIN DRY. HIGH TEMPERATURES TODAY
ARE LITTLE TRICKY, GENERALLY IN THE LOWER 70S NORTH TO UPPER 70S
SOUTH BUT IF ENOUGH SUNSHINE MATERIALIZES, THESE TEMPS COULD BE
A FEW TO POSSIBLY SEVERAL DEGREES TOO COOL. NORTHEAST WINDS
WILL ALLOW WAVES TO BUILD INTO THE 3 TO 6 FOOT RANGE AT IL LAKE
MICHIGAN BEACHES AND THE CURRENT BEACH HAZARD STATEMENT LOOKS
ON TRACK. EAST/SOUTHEAST WINDS WILL INCREASE AGAIN OVERNIGHT
INTO SATURDAY MORNING AND ANOTHER BEACH HAZARD STATEMENT MAY BE
NEEDED.
ATTENTION THEN SHIFTS TO WHAT IS EXPECTED TO BE DEVELOPING
CONVECTION ACROSS NORTHERN IA AND SOUTHWEST WI LATER THIS
EVENING WHICH IS THEN EXPECTED TO SPREAD INTO NORTHERN IL EARLY
SATURDAY MORNING. STILL SOME UNCERTAINTY FOR TIMING BUT THE TIME
PERIOD OF CONCERN SEEMS TO BE FOCUSED ON 09Z TO 15Z SATURDAY.
WITH PRECIPITABLE WATER VALUES DURING THIS TIME IN THE 2 INCH
RANGE, VERY HEAVY RAIN IS EXPECTED AND IF IT TRAINS OVER THE
SAME AREAS, FLOODING AND LOCALIZED FLASH FLOODING WILL BE
POSSIBLE. WHILE A FLOOD WATCH MAY BE NEED FOR PARTS OF THE AREA,
THIS TIME PERIOD IS STILL 24 HOURS AWAY AND THERE REMAINS
UNCERTAINLY FOR HOW FAR SOUTH INTO THE CWA A FLOOD WATCH MAY BE
NEEDED. THEREFORE, NO FLOOD WATCH HEADLINE IS PLANNED THIS
MORNING.
TRENDS FOR SATURDAY AFTERNOON INTO SATURDAY NIGHT WILL LIKELY BE
DETERMINED WITH HOW THE CONVECTION SATURDAY MORNING MATERIALIZES
AND THERE IS SOME CONCERN THAT ADDITIONAL THUNDERSTORMS WILL
REDEVELOP IN THE AFTERNOON THOUGH THERE IS QUITE A BIT OF
UNCERTAINTY. SPC DAY2 OUTLOOK HAS A LEVEL 1 SEVERE RISK FOR
LOCALIZED DAMAGING WINDS FOR MOST OF THE AREA ON SATURDAY.
ANOTHER PERIOD OF HEAVY RAIN IS EXPECTED SATURDAY NIGHT INTO
SUNDAY MORNING, BUT CONFIDENCE FOR WHERE THIS SETS UP IS LOW.
THOUGH IF IT DOES TAKE AIM A THE LOCAL AREA, THEN ANOTHER FLOOD
WATCH COULD POTENTIALLY BE NEEDED DURING THIS TIME PERIOD AS
WELL.
AS WINDS TURN NORTHEAST MONDAY INTO TUESDAY, COOLER AIR WILL
SPREAD ACROSS THE REGION WITH HIGH TEMPERATURES POSSIBLY ONLY
REACHING THE LOWER/MID 60S BOTH DAYS, WELL BELOW NORMAL FOR MID
SEPTEMBER. PERSISTENT AND AT TIMES, STRONG NORTHEAST WINDS WILL
ALLOW WAVES TO BUILD ALONG THE IL/IN LAKE MICHIGAN SHORE WITH
HIGH WAVES AND DANGEROUS CURRENTS EXPECTED DURING THIS TIME
PERIOD. CMS
AVIATION /06Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 1247 AM CDT FRI SEP 18 2026
KEY AVIATION FORECAST MESSAGES:
- IFR-MVFR CEILINGS GRADUALLY LIFTING TO VFR THIS MORNING,
LATEST AT RFD.
- SHRA/TSRA POTENTIAL RAMPS UP LATE TONIGHT INTO SATURDAY
MORNING, WITH MVFR/IFR CONDITIONS POSSIBLE IN HEAVY CONVECTIVE
SHRA/TS.
SURFACE HIGH PRESSURE BUILDING EAST-SOUTHEAST ACROSS ONTARIO AND
THE NORTHERN GREAT LAKES WAS BRINING SLIGHTLY DRIER NORTH-
NORTHEAST SURFACE WINDS TO THE REGION EARLY THIS MORNING, AND
HELPING TO PUSH THE DOWNSTATE FRONTAL ZONE FARTHER SOUTH. AREA
OF IFR CIGS WAS GRADUALLY IMPROVING TO LOW-MVFR FROM THE
NORTHEAST ACROSS THE TERMINALS AT 0530Z, AND SURFACE/SATELLITE
OBS AND HIGH-RES MODEL GUIDANCE SUPPORT GRADUAL CONTINUED
IMPROVEMENT TO HIGH-END MVFR/VFR THROUGH THIS MORNING WITH RFD
LIKELY SLOWEST TO IMPROVE TO VFR TOWARD MID-MORNING.
SURFACE WINDS SHOULD TURN MORE EAST-NORTHEAST DURING THE DAY AS
THE SURFACE HIGH CONTINUES TO MOVE OFF TO OUR NORTHEAST, AND
EVENTUALLY TO MORE OF AN EAST-SOUTHEAST DIRECTION TONIGHT AS AN
AREA OF LOW PRESSURE DEVELOPS INTO IA. AS THIS OCCURS, THE
FRONTAL BOUNDARY TO OUR SOUTH WILL GRADUALLY RETURN NORTHWARD
AS A WARM FRONT, WITH AN EXPANSION OF SHRA/TSRA DEVELOPING
ACROSS THE UPPER MISSISSIPPI VALLEY NEAR AND NORTH OF THE
SURFACE LOW AND WARM FRONT. WHILE A FEW SPOTTY SHOWERS CAN'T BE
COMPLETELY RULED OUT AS EARLY AS THIS AFTERNOON ESPECIALLY
ACROSS NORTHWEST IL/SOUTHERN WI, THE GREATEST POTENTIAL FOR MORE
WIDESPREAD AND IMPACTFUL HEAVY SHRA/TSRA ACROSS THE TERMINALS
APPEARS TO BE AFTER 06Z FOR RFD AND AFTER 08/09Z FOR THE
CHICAGO TERMINALS. A PROLONGED PERIOD OF SHRA/TSRA COULD THEN
PERSIST INTO MID-MORNING SATURDAY, WITH MVFR/IFR VIS/CIG
CONDITIONS.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...BEACH HAZARDS STATEMENT FROM 5 AM CDT EARLY THIS MORNING
THROUGH THIS AFTERNOON FOR ILZ006-ILZ103-ILZ104.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 7 AM THIS MORNING TO 3 PM CDT THIS
AFTERNOON FOR WINTHROP HARBOR TO WILMETTE HARBOR IL.
VISIT US AT WEATHER.GOV/CHICAGO
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