468
FXUS63 KLOT 190534
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1234 AM CDT SAT SEP 19 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. A
FLOOD WATCH FOR FLASH FLOODING IS IN EFFECT FOR MUCH OF
NORTHERN ILLINOIS AND FAR NORTHWEST INDIANA LATE TONIGHT
THROUGH SATURDAY MORNING.
- BELOW NORMAL TEMPS EARLY NEXT WEEK THEN DRY WEATHER EXPECTED
MID/LATE NEXT WEEK.
DISCUSSION
ISSUED AT 257 PM CDT FRI SEP 18 2026
AN UNSEASONABLY STRONG MID-LEVEL RIDGE WITH 500 HPA HEIGHTS UP
TO 600 DAM OVER TEXAS CONTINUES TO EXPAND ENE TOWARD THE MID-
MISSISSIPPI RIVER AND OHIO RIVER VALLEYS THIS AFTERNOON. INITIAL
ASCENT ON THE PERIPHERY OF THE RIDGE HAS MAINTAINED A GENERAL
NNW TO SSE AXIS OF HIGH-BASED SHOWERS DRIFTING ACROSS THE
FORECAST AREA THIS AFTERNOON. A DIMINISHING RESERVOIR OF MUCAPE
WITH EASTWARD EXTENT ACROSS THE NORTH HALF OF ILLINOIS HAS
ALLOWED SOME SPARSE EMBEDDED LIGHTNING TO APPROACH THE FAR WEST
AND SOUTHWEST CWA. OVERALL EXPECTATIONS ARE FOR ISOLATED TO
SCATTERED SHOWERS TO CONTINUE TRACKING ACROSS THE REMAINDER OF
THE CWA THROUGH EARLY EVENING. CLEARING HAS LEAD TO SURFACE-
BASED DESTABILIZATION BEHIND AN EFFECTIVE SURFACE FRONT OVER
CENTRAL ILLINOIS. WHILE STRONGER CONVECTION HAS BRUSHED THE
EXTREME SOUTHERN CWA, REMAINING ACTIVITY IS EXPECTED TO REMAIN
SOUTH THIS AFTERNOON.
APPRECIABLE DEEP LAYER ASCENT DRIVEN BY A MID/UPPER-LEVEL JET
CORE PASSING NORTH OF THE AREA TONIGHT AND AN APPROACHING
COMPACT MID-LEVEL WAVE CURRENTLY OVER SOUTHWEST NEBRASKA WILL
INTERACT WITH AN EXPANSIVE MUCAPE RESERVOIR ADVECTING
NORTHEASTWARD TOWARD THE AREA TONIGHT. CONVECTION WILL LIKELY
QUICKLY DEVELOP OVER FAR NORTHERN IOWA LATE THIS EVENING AND
EXPAND EASTWARD TO SOUTHERN WISCONSIN IN RESPONSE TO A
STRENGTHENING LLJ FOCUSED TOWARD FAR SOUTHWEST WISCONSIN
OVERNIGHT. WITH THE VEERING LLJ BECOMING NEARLY PERPENDICULAR TO
THE LOW-LEVEL FRONT, SIGNIFICANTLY HIGH PWAT VALUES AT OR ABOVE
2 INCHES (NEARLY 250 PERCENT OF NORMAL FOR THE SECOND HALF OF
SEPTEMBER), AND RELATIVELY SLOW STORM MOTIONS, THERE IS GROWING
CONCERN THAT AN AXIS OF SIGNIFICANT RAINFALL DEVELOPS JUST NORTH
OF THE IL/WI STATE LINE OVERNIGHT. THIS ACTIVITY WOULD THEN
SLOWLY TRANSLATE SOUTHWARD OVER NORTHERN ILLINOIS TOWARD
DAYBREAK AND THROUGH AT LEAST MID-MORNING. RAINFALL RATES OF 2
INCHES PER HOUR OR HIGHER (SIMILAR TO WHAT WAS OBSERVED EARLY
THURSDAY MORNING), COULD LEAD TO FLASH FLOODING, ESPECIALLY FOR
URBANIZED AREAS AROUND ROCKFORD AND THE CHICAGO METRO. A FLOOD
WATCH FOR FLASH FLOODING HAS BEEN ISSUED FOR A VAST MAJORITY OF
THE CHICAGO METRO AND AREAS AROUND AND NORTH OF I-88 LATE
TONIGHT THROUGH SATURDAY MORNING, WITH THE GREATEST CONCERN IN
THE 5-10AM WINDOW. SEVERE THUNDERSTORMS ARE NOT EXPECTED AS THIS
ACTIVITY WILL REMAIN ELEVATED, BUT LOCALIZED SUB-SEVERE GUSTS
CANNOT BE RULED OUT.
CONVECTION MAY FESTER OVER SOME OF THE AREA LATE MORNING
THROUGH MUCH OF THE AFTERNOON, BUT COVERAGE IS EXPECTED TO
REMAIN LOW. THE LOW-LEVEL ENVIRONMENT WILL QUICKLY DESTABILIZE
TO THE SOUTHWEST SATURDAY AFTERNOON, WITH THE ASSOCIATED AIRMASS
BEGINNING TO ADVECT NORTHEASTWARD TOWARD THE FORECAST AREA.
ANOTHER MID-LEVEL WAVE CURRENTLY OVER SOUTHEAST COLORADO IS
PROGGED TO CROSS SOUTHERN WISCONSIN VERY LATE IN THE AFTERNOON
AND EVENING, ALIGNING WITH A SLOW-MOVING SURFACE LOW AND
INITIATING RENEWED CONVECTION OVER OR JUST NORTH OF THE STATE
LINE BY EARLY EVENING. ORGANIZED STRONG TO MARGINALLY SEVERE
CONVECTION CANNOT BE RULED OUT IN A NARROW CORRIDOR WEST OF THE
I-39 CORRIDOR WHERE LOW-LEVEL DESTABILIZATION, DELAYED LOW-LEVEL
WARMING/CAPPING, AND MODEST LOW-LEVEL SHEAR SUPPORT A VERY
CONDITIONAL LOCALIZED DAMAGING WIND AND BRIEF TORNADO THREAT
LATE AFTERNOON INTO EARLY EVENING.
THE FLOODING RISK WILL INCREASE AGAIN WITH THE EVENING
CONVECTION AS MOST INGREDIENTS FOR FLOODING PRESENT IN THE
MORNING WILL REMAIN IN PLACE DURING THE EVENING. CONVECTION MAY
THEN STALL SOMEWHERE OVER THE CENTRAL OR SOUTHERN CWA OVERNIGHT
INTO SUNDAY MORNING AS THE LOW-LEVEL JET STRENGTHENS AND VEERS,
LEADING TO THE POTENTIAL FOR A LOCAL CORRIDOR OF SIGNIFICANT
RAINFALL TOTALS AND ADDITIONAL FLOODING. A NEW FLOOD WATCH WILL
LIKELY BE REQUIRED FOR MUCH OF THE NIGHT FOR A LARGE PORTION OF
THE FORECAST AREA.
WHILE STRONG HIGH PRESSURE BUILDING ACROSS ONTARIO AND QUEBEC
THROUGH EARLY NEXT WEEK SHOULD PROVIDE A FEED OF FAIRLY DRY AIR
TOWARD THE AREA, ANOTHER COMPACT MID-LEVEL LOW TRAVERSING THE
EFFECTIVE COLD FRONT MAY RESULT IN ADDITIONAL HEAVY RAIN ACROSS
CENTRAL ILLINOIS, INCLUDING SOME OF THE FORECAST AREA, ON
MONDAY. DRY AND COOL CONDITIONS WILL THEN BECOME MORE FAVORED
BEGINNING TUESDAY AND ESPECIALLY LATER IN THE WEEK.
KLUBER
AVIATION /06Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 1234 AM CDT SAT SEP 19 2026
KEY AVIATION FORECAST MESSAGES:
- SHRA/TSRA DEVELOP INTO FAR NORTHERN IL 07-10Z THIS MORNING
WITH TSRA AND NEAR-LIFR VISIBILITY IN HEAVY RAIN THROUGH MUCH
OF THE MORNING.
- SHRA AND MVFR CEILINGS PERSIST AT TIMES THIS AFTERNOON INTO
TONIGHT, WITH ANOTHER ROUND OF TSRA POSSIBLE THIS EVENING INTO
THE OVERNIGHT HOURS.
SHRA/TSRA CONTINUE TO DEVELOP ACROSS SOUTHERN WI IN RESPONSE TO
LOW-LEVEL JET FORCING ATOP AN ELEVATED WARM FRONTAL ZONE.
GUIDANCE REMAINS IN GOOD AGREEMENT THAT THIS CONVECTION WILL
CONTINUE TO DEVELOP EAST-SOUTHEASTARD OVER THE NEXT FEW HOURS
AND IMPACT THE TERMINALS FOR A PROLONGED PERIOD INTO MID-LATE
MORNING. WHILE TS COVERAGE SHOULD DIMINISH BY MIDDAY, SCATTERED
SHRA MAY PERSIST AS WEAK, MOIST ASCENT PERSISTS WITHIN THE
WARM FRONTAL ZONE. ANOTHER MID-LEVEL WAVE CURRENTLY EMERGING
FROM THE HIGH PLAINS IS PROGGED TO APPROACH THE FORECAST AREA
FROM THE WEST THIS EVENING, WITH ANOTHER INCREASE IN SHRA AND
TSRA COVERAGE LIKELY TONIGHT.
MVFR CEILINGS (ALREADY IN PLACE AT RFD AT ISSUANCE) ARE
EXPECTED TO BECOME WIDESPREAD THIS MORNING AND PERSIST THROUGH
THE PERIOD, WITH IFR CIGS POSSIBLE AT TIMES. IFR TO NEAR-LIFR
VSBYS ARE POSSIBLE IN HEAVIER SHRA/TSRA THIS MORNING AND AGAIN
TONIGHT.
SURFACE WINDS ARE EXPECTED TO REMAIN GENERALLY EAST-SOUTHEAST TO
SOUTHEAST ACROSS THE TERMINALS, THOUGH MAY BECOME MORE SOUTHERLY
AT RFD (AND POSSIBLY DPA) LATER TODAY DEPENDING ON HOW FAR
NORTH A SURFACE LOW PRESSURE WAVE AND SURFACE WARM FRONT LIFT
INTO THE REGION. TSRA MAY ALSO TEMPORARILY PRODUCE GUSTY, MORE
NORTHERLY SURFACE WINDS.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH THROUGH THIS AFTERNOON FOR ILZ003-ILZ004-ILZ005-
ILZ008.
BEACH HAZARDS STATEMENT THROUGH THIS EVENING FOR ILZ006.
FLOOD WATCH FROM 4 AM CDT EARLY THIS MORNING THROUGH THIS
AFTERNOON FOR ILZ006-ILZ010-ILZ011-ILZ012-ILZ013-ILZ020-
ILZ103-ILZ104-ILZ105-ILZ106.
BEACH HAZARDS STATEMENT THROUGH THIS AFTERNOON FOR ILZ103-
ILZ104.
IN...FLOOD WATCH FROM 4 AM CDT EARLY THIS MORNING THROUGH THIS
AFTERNOON FOR INZ001-INZ002.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CDT THIS AFTERNOON FOR
WINTHROP HARBOR TO NORTHERLY IS. IL.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page