162
FXUS63 KILX 071840
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
140 PM CDT MON SEP 7 2026
KEY MESSAGES
- SUMMER HEAT AND HUMIDITY RETURN TUESDAY AND WEDNESDAY. HEAT
INDICES ARE FORECAST TO EXCEED 100 DEGREES WEDNESDAY
AFTERNOON, MAINLY SOUTH OF INTERSTATE 72.
- RAIN AND THUNDERSTORMS MOVE IN WEDNESDAY AND WEDNESDAY NIGHT,
BRINGING A 0.25 TO 0.75-INCH AVERAGE RAINFALL. THERE IS A 10%
CHANCE FOR LOCALIZED RAIN TOTALS OVER 1.0 TO 1.5
DISCUSSION
ISSUED AT 135 PM CDT MON SEP 7 2026
TODAY THROUGH TONIGHT
A WELCOME BREAK FROM THE RECENT HEAT WAVE CONTINUES THE REST OF
TODAY UNDER THE INFLUENCE OF A SURFACE RIDGE CENTERED OVER THE
GREAT LAKES. THIS HIGH IS MAINTAINING A MODEST EASTERLY BREEZE
ACROSS CENTRAL ILLINOIS, DRAWING IN A MUCH DRIER AIRMASS WITH
DEWPOINTS IN THE UPPER 50S TO LOWER 60S. HIGH TEMPERATURES THIS
AFTERNOON WILL TOP OUT IN THE LOW TO MID 80S UNDER MOSTLY SUNNY
SKIES, FOLLOWED BY A QUIET AND COMFORTABLE NIGHT WITH LOWS IN
THE LOWER 60S.
TUESDAY AND WEDNESDAY (RETURN OF SUMMER HEAT)
THE RESPITE FROM THE HEAT WILL BE SHORT-LIVED AS SUMMER-LIKE
CONDITIONS RETURN. AN UPPER-LEVEL LOW CURRENTLY OVER THE PACIFIC
NORTHWEST IS PROJECTED TO TRACK EASTWARD INTO THE CANADIAN
PRAIRIES BY TUESDAY, FLATTENING THE STRONG CENTRAL U.S. UPPER
RIDGE AND PUSHING ITS WARM EASTERN PERIPHERY BACK ACROSS THE
MIDWEST. AN ASSOCIATED 850MB THERMAL RIDGE (WITH TEMPERATURES
CLIMBING TO 22-24C, REMINISCENT OF THE RECENT HEAT WAVE) WILL
SHIFT OVER CENTRAL ILLINOIS TUESDAY, THEN PROGRESS INTO SOUTHERN
ILLINOIS BY WEDNESDAY. HIGHS WILL SURGE BACK INTO THE 90S
ACROSS MOST OF CENTRAL ILLINOIS ON TUESDAY.
FORTUNATELY, SOUTHERLY FLOW WILL NOT BE ESTABLISHED LONG ENOUGH
BY TUESDAY AFTERNOON FOR NOTABLE MOISTURE RETURN; DEEP BOUNDARY
LAYER MIXING WILL KEEP DEWPOINTS RELATIVELY LOW (LOW TO MID
60S), HOLDING HEAT INDICES IN CHECK IN THE LOW TO MID 90S.
MOISTURE RETURNS IN EARNEST ON WEDNESDAY AS SOUTHWESTERLY FLOW
STRENGTHENS AHEAD OF AN APPROACHING COLD FRONT. THIS FLOW WILL
TRANSPORT A MUCH MUGGIER AIRMASS INTO THE REGION, BOOSTING
DEWPOINTS INTO THE LOW TO MID 70S. COMBINED WITH TEMPERATURES IN
THE LOW TO MID 90S, HEAT INDICES ARE EXPECTED TO EXCEED 100
DEGREES IN SEVERAL LOCATIONS WEDNESDAY AFTERNOON, PARTICULARLY
SOUTH OF THE I-72 CORRIDOR.
WEDNESDAY THROUGH THURSDAY (COLD FRONT & STORM POTENTIAL)
THE COLD FRONT IS MODELED TO CROSS CENTRAL ILLINOIS MID-TO-
LATE WEDNESDAY MORNING. DUE TO THE TIMING NEAR THE DIURNAL
INSTABILITY MINIMUM, INSTABILITY WILL BE WEAK (GFS MLCAPE VALUES
AT OR BELOW 500 J/KG), AND INITIAL CONVECTION IS EXPECTED TO BE
IN A DECAYING PHASE AS IT ENTERS THE AREA. HOWEVER, THE FRONTAL
BOUNDARY IS PROJECTED TO SLOW AND STALL AS IT MOVES SOUTH
ACROSS THE I-72 AND I-70 CORRIDORS WEDNESDAY EVENING INTO
WEDNESDAY NIGHT. A SECOND ROUND OF CONVECTION IS EXPECTED TO
DEVELOP ALONG A MODEST LOW-LEVEL JET TO OUR WEST AND TRACK
EASTWARD ALONG THE STALLING BOUNDARY OVERNIGHT. TOTAL RAINFALL
THROUGH THURSDAY IS FORECAST TO AVERAGE 0.25 TO 0.50 INCHES
NORTH OF I-72/DANVILLE, AND 0.50 TO 0.75 INCHES TO THE SOUTH.
THE 90TH PERCENTILE GUIDANCE SUGGESTS LOCALIZED TRAINING OF
STORMS COULD PRODUCE ISOLATED STREAKS OF 1.0 TO 1.5 INCHES.
FRIDAY THROUGH SUNDAY
HIGH PRESSURE WILL BUILD ACROSS THE UPPER MIDWEST BEHIND THE
FRONT ON THURSDAY, GRADUALLY SHIFTING EAST ACROSS THE GREAT
LAKES BY FRIDAY. WHILE DRY WEATHER WILL PREVAIL FURTHER NORTH
UNDER THE INFLUENCE OF THIS RIDGE, SOME PRECIPITATION CHANCES
WILL LINGER ACROSS CENTRAL AND SOUTHERN ILLINOIS IN THE VICINITY
OF THE STALLED FRONTAL BOUNDARY. THE UPPER-LEVEL PATTERN IS
MODELED TO FLATTEN FURTHER OVER THE WEEKEND, WITH LOW-AMPLITUDE
WAVES IN THE ZONAL FLOW BRINGING PERIODIC CHANCES FOR SHOWERS
AND STORMS. DUE TO LOW PREDICTABILITY AND MODEL SPREAD, BROAD-
BRUSHED 20-30% POPS REMAIN IN PLACE FROM FRIDAY THROUGH EARLY
NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1204 PM CDT MON SEP 7 2026
HIGH PRESSURE IS CENTERED OVER THE GREAT LAKES LATE THIS
AFTERNOON AND WILL DRIFT EAST TO THE ATLANTIC COAST WHILE A
COLD FRONT APPROACHES CENTRAL ILLINOIS FROM THE UPPER MIDWEST
LATE TUESDAY. LIGHT EAST/SOUTHEAST WINDS WILL AND VFR CONDITIONS
CONTINUE TODAY UNDER THE INFLUENCE OF THE RIDGE. WINDS SET UP
OUT OF THE S/SSW TUESDAY MORNING AHEAD OF THE APPROACHING FRONT.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...DEUBELBEISS
DISCUSSION...DEUBELBEISS
AVIATION...DEUBELBEISS
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