947
FXUS63 KILX 160609
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
109 AM CDT WED SEP 16 2026
KEY MESSAGES
- HEAVY RAIN & LOCALIZED FLASH FLOODING: REPEATED RAINFALL ALONG
A STALLED FRONT PRESENTS A LOCALIZED FLASH FLOOD THREAT EARLY
THIS MORNING THROUGH MIDDAY TODAY NORTH OF THE BOUNDARY.
LOCALIZED POCKETS OF RAINFALL TOTALING 3 TO 7 INCHES ARE
POSSIBLE, PRIMARILY ACROSS CENTRAL ILLINOIS ALONG AND NORTH OF
I-72.
- ISOLATED STRONG STORMS: ISOLATED STRONG THUNDERSTORMS MAY
PRODUCE LOCALIZED DAMAGING WINDS THIS AFTERNOON AND EVENING
NEAR THE I-72 CORRIDOR, WITH A LOW-END THREAT CONTINUING
THURSDAY AND FRIDAY.
- DANGEROUS HEAT & HUMIDITY: SWELTERING CONDITIONS WILL CONTINUE
SOUTH OF I-72 TODAY, WHERE HIGH HUMIDITY WILL DRIVE HEAT
INDICES TO 100-104F.
- UNSETTLED PATTERN & TEMPERATURE CONTRAST: DAILY SHOWER AND
STORM CHANCES PERSIST INTO EARLY NEXT WEEK ALONGSIDE A SHARP
CONTRAST BETWEEN 90S SOUTH AND 80S NORTH, BEFORE COOLER AIR
STARTS TO FILTER IN LATE THIS WEEKEND INTO EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 1258 AM CDT WED SEP 16 2026
SHORT TERM... (TODAY THROUGH THURSDAY)
A STALLED SURFACE BOUNDARY CURRENTLY POSITIONED BETWEEN THE
I-72 AND I-70 CORRIDORS STRETCHING WEST-SOUTHWEST INTO CENTRAL
MISSOURI REMAINS THE MAIN DRIVER FOR ACTIVE WEATHER ACROSS THE
REGION. ELEVATED CONVECTION CONTINUES EARLY THIS MORNING NORTH
OF THE BOUNDARY, SUSTAINED BY BROAD SOUTHWESTERLY FLOW ALOFT
TAPPING INTO 1500 J/KG MUCAPE (ROOTED BETWEEN 800-900 MB).
WHILE THE SEVERE THREAT REMAINS LOW EARLY THIS MORNING IN THIS
ELEVATED REGIME, TRAINING CONVECTION PARALLEL TO THE SURFACE
FRONT PRESENTS A LOCALIZED HEAVY RAINFALL HAZARD. HREF LPMM
GUIDANCE HIGHLIGHTS A BROAD 1-3 INCH SWATH OF RAINFALL ACROSS
CENTRAL ILLINOIS NORTH OF THE FRONT, WITH LOCALIZED HIGH-END
POCKETS BETWEEN 3-7 INCHES. WITH 1-HR FLASH FLOOD GUIDANCE
(FFG) AROUND 2.0 INCHES AND 3-HR FFG BETWEEN 2.75-3.00 INCHES,
AN ISOLATED FLASH FLOOD WARNING OR TWO REMAINS POSSIBLE THROUGH
MIDDAY TODAY.
BY THIS AFTERNOON, THE FRONTAL BOUNDARY IS EXPECTED TO INCH
NORTHWARD, BECOMING ORIENTED ALONG OR NEAR THE I-72 CORRIDOR.
STRONG DIURNAL HEATING WITHIN THE WARM SECTOR WILL YIELD MLCAPE
VALUES PEAKING AROUND 2500 J/KG. DEEP-LAYER SHEAR REMAINS
SOMEWHAT MARGINAL (0-6KM SHEAR VECTORS OF 20-30 KT, PEAKING NEAR
30 KT ALONG THE NORTHERN EDGE OF THE INSTABILITY AXIS), BUT
PARAMETER SPACE WILL SUPPORT ISOLATED STRONG PULSE CONVECTION
THIS AFTERNOON AND EVENING.
A SHARP THERMAL GRADIENT WILL SPAN THE AREA TODAY: TEMPERATURES
WILL CLIMB WELL INTO THE 90S SOUTH OF I-72, WHERE LOW-TO-MID 70S
DEWPOINTS WILL PRODUCE PEAK HEAT INDICES BETWEEN 100-104F. A
FEW ISOLATED SPOTS MAY TOUCH HEAT ADVISORY CRITERIA (105F), BUT
LOW CONFIDENCE IN WIDESPREAD COVERAGE PRECLUDES HEAT HEADLINE
ISSUANCE AT THIS TIME. FURTHER NORTH, TEMPERATURES WILL TRAIL
OFF THROUGH THE 80S, WITH UPPER 70S CLIPPING NORTHERN COUNTIES
(KNOX THROUGH MARSHALL).
LONG TERM... (THURSDAY NIGHT THROUGH NEXT WEDNESDAY)
A STRONG CANADIAN HIGH TRACKING FROM MANITOBA (THURSDAY) TO
QUEBEC (SATURDAY) WILL INITIALLY PUSH THE SURFACE BOUNDARY SOUTH
ACROSS CENTRAL ILLINOIS BEFORE SOUTHERLY RETURN FLOW NUDGES IT
BACK NORTHWARD LATE IN THE WEEK. THE PERSISTING FRONTAL BOUNDARY
OVER THE REGION WILL MAINTAIN DAILY PRECIPITATION CHANCES
ALONGSIDE A SHARP NORTH-TO-SOUTH TEMPERATURE CONTRAST (MID 90S
SOUTH, LOW 80S NORTH). STRONG DIURNAL DESTABILIZATION COMBINED
WITH MODEST DEEP-LAYER SHEAR WILL KEEP A LOW-END THREAT FOR A
FEW STRONGER STORMS IN PLACE THURSDAY AND FRIDAY.
A BROADER SYNOPTIC PATTERN CHANGE ARRIVES LATE WEEKEND AS THE
UPPER-LEVEL RIDGE CENTERED OVER THE SOUTHERN/SOUTHEASTERN CONUS
BREAKS DOWN. AN UPPER LOW TRACKING ACROSS THE NORTHERN GREAT
PLAINS INTO THE UPPER MIDWEST WILL SWEEP ANOTHER ROUND OF
SHOWERS AND THUNDERSTORMS THROUGH THE REGION ON SUNDAY. COOLER
AIR FILTERING IN BEHIND THIS SYSTEM WILL FINALLY PUSH 90-DEGREE
TEMPERATURES SOUTH OF THE AREA THROUGH THE FIRST HALF OF NEXT
WEEK WHILE PRECIP CHANCES GRADUALLY BECOME MORE MUTED IN THE
DRIER AIR MASS..
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1214 AM CDT WED SEP 16 2026
A COLD FRONT HAS STALLED ACROSS CENTRAL IL AND IS PROJECTED TO
REMAIN IN PLACE THROUGH TOMORROW MORNING. THE MOST LIKELY
SCENARIO IS FOR PERIODIC SHOWERS AND STORMS TO IMPACT ALL
TERMINALS THROUGH AT LEAST 10Z BUT POSSIBLY 12Z. WE WILL
CONTINUE THE FORECAST FOR PREDOMINANT -TSRA AT ALL SITES BETWEEN
06Z-12Z AS ACTIVITY MOVES FROM WEST TO EAST ALONG THE FRONT.
HEAVY RAINFALL COULD PRODUCE EXTENDED PONDING OF WATER ON TRAVEL
SURFACES AT THE AIRPORTS DURING THAT TIME. IN THE WAKE OF THE
THUNDERSTORM ACTIVITY, LOW STRATUS WILL BUILD DOWN INTO THE IFR
RANGE THROUGH SUNRISE, GRADUALLY IMPROVING TO VFR BETWEEN
18Z-21Z AS THE STALLED FRONT BEGINS TO SHIFT NORTH OF THE
TERMINALS. WIND SPEEDS OUTSIDE OF ANY STORMS WILL PREVAIL IN THE
6 TO 10 KT RANGE FROM THE NORTHEAST.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...DEUBELBEISS
DISCUSSION...DEUBELBEISS
AVIATION...SHIMON
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