457
FXUS63 KILX 041730
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1230 PM CDT THU JUN 4 2026
KEY MESSAGES
- A MARGINAL RISK FOR SEVERE THUNDERSTORMS EXISTS ON FRIDAY,
WITH ISOLATED DAMAGING WIND GUSTS SERVING AS THE PRIMARY RISK.
- AN UNSETTLED WEATHER PATTERN WILL BRING DAILY CHANCES OF
SHOWERS AND THUNDERSTORMS FRIDAY THROUGH THE MIDDLE OF NEXT
WEEK.
- HUMIDITY BUILDS OVER CENTRAL AND SOUTHEAST ILLINOIS THIS
WEEKEND AND LINGERS INTO NEXT WEEK, DRIVING PEAK HEAT INDEX
VALUES INTO THE LOW TO MID 90S.
DISCUSSION
ISSUED AT 133 AM CDT THU JUN 4 2026
HIGH PRESSURE SLIDES EASTWARD TODAY, ALLOWING A RETURN TO
SOUTHERLY BOUNDARY-LAYER FLOW AND GRADUALLY INCREASING DEWPOINTS
THROUGH THE 50S. AFTERNOON RH SHOULD DROP TO AROUND 35-40%, AND
WITH WINDS GUSTING 20-25 MPH AT TIMES THERE WILL BE A LOW RISK
FOR FIRE SPREAD, AS WELL AS LOCALIZED BLOWING DUST WHERE
FARMING ACTIVITY IS IN PROGRESS. HIGH TEMPERATURES WILL AGAIN
PEAK IN THE MID-80S.
A FRONTAL BOUNDARY MOVES TOWARD CENTRAL AND SOUTHEAST ILLINOIS
ON FRIDAY. INSTABILITY CLIMBS SUBSTANTIALLY AS LOW- LEVEL
MOISTURE DEEPENS, PUSHING SURFACE DEWPOINTS INTO THE UPPER 60S.
THE HREF INDICATES A 40-50% PROBABILITY OF SURFACE-BASED CAPE
EXCEEDING 2000 J/KG ACROSS THE FORECAST AREA BY FRIDAY
AFTERNOON. HOWEVER, GUIDANCE REVEALS A WEAK KINEMATIC
ENVIRONMENT, WITH 0-6 KM BULK SHEAR REMAINING UNDER 20 KNOTS.
DUE TO THIS COMBINATION OF MODERATE INSTABILITY AND LOW SHEAR,
THE SPC HAS OUTLINED A MARGINAL RISK (LEVEL 1/5) OF SEVERE
WEATHER NORTH OF A RUSHVILLE TO BLOOMINGTON LINE. THE PRIMARY
THREAT WILL BE ISOLATED DAMAGING WIND GUSTS STEMMING FROM PULSE
OR MULTICELL STORM COLLAPSES. OUTSIDE OF CONVECTIVE ACTIVITY, A
TIGHTENING PRESSURE GRADIENT WILL CAUSE SOUTHWESTERLY WIND GUSTS
TO EXCEED 25 MPH AT TIMES.
A LONG-DURATION, UNSETTLED WEATHER PATTERN WILL DOMINATE THE
REGION THIS WEEKEND THROUGH THE MIDDLE OF NEXT WEEK. GEFS AND
EPS ENSEMBLE MEANS STRONGLY FAVOR A BLOCKED, SLOW- MOVING
SYNOPTIC PATTERN THROUGH THE PERIOD. A CUTOFF UPPER-LEVEL LOW OR
SLOW-MOVING TROUGH IS FORECAST TO DEVELOP AND MEANDER ACROSS
THE MIDWEST, WHILE A WEAK FRONTAL BOUNDARY WAVERS ACROSS THE
AREA. DUE TO WEAK FORCING, CONFIDENCE IN TIMING AND RAINFALL
AMOUNTS IS LOW, THOUGH CONFIDENCE IN A PROLONGED WARM/HUMID AND
FREQUENTLY WET PATTERN IS HIGH. WEAK SHEAR THROUGHOUT THIS
PERIOD WILL MINIMIZE ORGANIZED SEVERE WEATHER, THOUGH LOCALIZED
HEAVY RAIN TOTALS AND ISOLATED GUSTY THUNDERSTORM WINDS WILL BE
POSSIBLE.
NBM GUIDANCE MAINTAINS AFTERNOON TEMPERATURES IN THE UPPER 80S
TO LOWER 90S THIS WEEKEND AND EARLY NEXT WEEK, WHILE DEWPOINTS
CLIMB INTO THE UPPER 60S TO LOWER 70S. THIS HUMID ENVIRONMENT
WILL DRIVE DAILY PEAK HEAT INDEX VALUES INTO THE LOW-MID 90S
THROUGH TUESDAY, AND AROUND 100 DEGREES ON WEDNESDAY WEST OF
I-55. THE ECMWF EXTREME FORECAST INDEX (EFI) HIGHLIGHTS THIS
AIRMASS AS CLIMATOLOGICALLY UNUSUAL FOR EARLY JUNE, PARTICULARLY
CONCERNING THE ELEVATED MOISTURE LEVELS. FURTHERMORE, THE
CLIMATE PREDICTION CENTER 6-10 DAY OUTLOOK INDICATES A STRONG
PROBABILITY (60-70% CHANCE) OF ABOVE- NORMAL TEMPERATURES ACROSS
THE REGION THROUGH THE END OF NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1230 PM CDT THU JUN 4 2026
VFR CONDITIONS REIGN OVER THE MAJORITY OF THE 18Z TAF PERIOD.
HOWEVER, TOMORROW MORNING (AFTER 14Z TOMORROW), SHOWERS AND
THUNDERSTORMS WILL MOVE INTO THE CENTRAL IL AREA, BRINGING MVFR
CEILINGS WITH IT. PIA WILL SEE THE <3000KFT CEILINGS FIRST. THE
COMPLEX OF SHOWERS AND THUNDERSTORMS WILL BE DECAYING AS IT
ARRIVES, THEREFORE THE PROB30 GROUPS WERE USED. CMI WILL BE THE
LAST SITE TO SEE PRECIPITATION NEARING THE END OF THE PERIOD.
WINDS WILL BE PREDOMINATELY OUT OF THE SOUTH-SOUTHWEST GUSTING
TO 20 KNOTS. THEY WILL RELAX BRIEFLY OVERNIGHT BEFORE INCREASING
AGAIN AS THE SUN STARTS TO RISE AHEAD OF THE PRECIPITATION
MOVING IN.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...25
DISCUSSION...25
AVIATION...COPPLE
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