995
FXUS63 KLOT 181130
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
630 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 /12Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 630 AM CDT FRI SEP 18 2026
KEY AVIATION FORECAST MESSAGES:
- A FEW VFR LIGHT SHRA POSSIBLE MIDDAY/EARLY AFTERNOON AT RFD.
- SHRA/TSRA EXPECTED TO DEVELOP ACROSS THE REGION PREDAWN
SATURDAY. 06Z MODEL GUIDANCE IS SLOWER WITH A SOMEWHAT SMALLER
FOOTPRINT OF CONVECTION THAN EARLIER RUNS, LEADING TO SOMEWHAT
LOWER CONFIDENCE ESPECIALLY IN TS COVERAGE/TIMING EARLY SAT.
SURFACE HIGH PRESSURE CONTINUES TO BUILD EAST-SOUTHEAST ACROSS
ONTARIO AND THE NORTHERN GREAT LAKES REGION THIS MORNING, WITH
NORTHEAST LOW-LEVEL FLOW ADVECTING DRIER AIR INTO THE REGION.
THIS HAS ALLOWED CONTINUED LIFTING AND SCATTERING OF EARLIER
MVFR DECK ACROSS THE TERMINALS, WITH EVEN RFD NOW JUST ABOVE 3
KFT. CAN'T COMPLETELY RULE OUT SOME BRIEF PATCHY 2500-3000 FOOT
BASES THIS MORNING AFTER SUNRISE, BUT OVERALL VFR CONDITIONS ARE
EXPECTED THROUGH THIS EVENING. NORTHEAST SURFACE WINDS ARE
EXPECTED TO INCREASE INTO THE 10-15 KT RANGE THIS MORNING AND
EVENTUALLY TURN MORE EASTERLY. SOME SPOTTY DECAYING SHRA ACROSS
EASTERN IA MAY REACH RFD BY MIDDAY IF THEY DON'T DISSIPATE
FIRST. HAVE ADDED A VFR PROB30 FOR LIGHT SHOWERS FOR THIS.
SURFACE LOW PRESSURE IS PROGGED TO DEVELOP FROM THE HIGH PLAINS
NORTHEASTWARD TOWARD THE UPPER-MISSISSIPPI VALLEY THROUGH
TONIGHT, TURNING LOCAL WINDS SOUTHEAST AND PULLING THE FRONTAL
BOUNDARY CURRENTLY OVER DOWNSTATE IL/IN BACK NORTH INTO THE
FORECAST AREA AS A WARM FRONT INTO SATURDAY MORNING. AS THIS
OCCURS, A SOUTHWESTERLY LOW LEVEL JET DEVELOPS INTO THE IA/MN/WI
BORDER REGION, PROVIDING ASCENT AND RETURNING MOISTURE WHICH IS
EXPECTED TO RESULT IN WIDESPREAD SHRA/TSRA DEVELOPMENT OVER
PARTS OF THE REGION. 00Z MODEL RUNS WERE IN DECENT AGREEMENT IN
DEVELOPING A DECENT SIZED FOOTPRINT OF SHRA/TS OVER NORTHERN IL
PREDAWN SATURDAY, THOUGH HAVE NOTED A SIGNIFICANT SLOWING AND
DECREASE IN THAT FOOTPRINT IN MANY OF THE 06Z MODEL RUNS. AM A
BIT HESITANT TO BACK OFF TOO MUCH ON SHRA/TSRA FORECAST EARLY
SATURDAY GIVEN DECENT FORCING AND MOISTURE AT PLAY, THOUGH DID
PUSH TIMING BACK A BIT LATER FROM THE 06Z TAFS. THIS MAY NEED
ADDITIONAL ADJUSTMENT WITH LATER UPDATES IF 12Z GUIDANCE SUITE
CONTINUES TO INDICATE A SIMILAR TREND AS THE 06Z SET. WOULD
EXPECT AT LEAST SOME MVFR CIG/VIS CONDITIONS IN ASSOCIATION WITH
SHRA/TS THAT OCCUR IN THIS SCENARIO.
RATZER
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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