088
FXUS63 KLOT 181748
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1248 PM 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 /18Z TAFS THROUGH 00Z SUNDAY/
ISSUED AT 1248 PM CDT FRI SEP 18 2026
A REGION OF SHOWERS WILL SLIDE OVER THE TERMINALS THIS
AFTERNOON TIED TO A WEAKENING MID-LEVEL WAVE. WITH A FEED OF DRY
AIR FROM THE EAST ON THE SOUTH SIDE OF A SURFACE HIGH OVER THE
GREAT LAKES REGION, SUSPECT THE SHOWERS WILL BE MORE OF A
NUISANCE THAN AN IMPACT WITH NO CIG OR VSBY RESTRICTION LOCALLY.
WILL MAINTAIN TEMPO GROUPS GENERALLY IN THE 19-22Z TIMEFRAME
FOR PLAIN SHOWERS.
TONIGHT, A LOW-LEVEL JET WILL DEVELOP OVER THE MIDDLE
MISSISSIPPI RIVER VALLEY AFFORDING A CONTINUATION OF EAST TO
SOUTHEASTERLY SURFACE WINDS. BROKEN MVFR CIGS MAY DEVELOP WITH
TIME ESPECIALLY TOWARD DAYBREAK AS THE LOW-LEVEL COLUMN
MOISTENS. MEANWHILE, A LARGE AREA OF THUNDERSTORMS IS EXPECTED
TO DEVELOP IN THE VICINITY OF NORTHERN IOWA AND SOUTHERN
WISCONSIN AND DROP SOUTHWARD ACROSS THE TERMINALS NEAR OR JUST
AFTER DAYBREAK. WILL MAINTAIN THE INHERITED STRUCTURE OF THE
TAFS WITH SHRA STARTING BY 09-10Z AND TEMPO GROUPS GENERALLY
FROM 12-15Z. CAN EASILY ENVISION TRANSITIONING THE TEMPO GROUPS
TO FM GROUPS IN A LATER TAF PACKAGE. A PERIOD OF NORTHWESTERLY
WINDS AND IFR CIGS MAY ACCOMPANY THE THUNDERSTORMS THROUGH THE
MORNING.
WITH CONTINUED ISENTROPIC ASCENT IN THE REGION, SUSPECT SHOWERS
WILL CONTINUE ON AND OFF UNABATED THROUGH THE LATE MORNING AND
EARLY AFTERNOON HOURS AS EASTERLY WINDS PREVAIL. DO SUSPECT
THERE MAY BE HOLES IN IFR AND MVFR CIGS THROUGH THE EARLY
AFTERNOON HOURS BEFORE LOW CIGS REDEVELOP AND SHOWER AND STORM
COVERAGE INCREASES ONCE AGAIN BY 00Z.
BORCHARDT
LOT WATCHES/WARNINGS/ADVISORIES
IL...BEACH HAZARDS STATEMENT UNTIL 3 PM CDT THIS AFTERNOON FOR
ILZ006-ILZ103-ILZ104.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CDT THIS AFTERNOON FOR
WINTHROP HARBOR TO WILMETTE HARBOR IL.
VISIT US AT WEATHER.GOV/CHICAGO
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