274
FXUS63 KILX 171937
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
237 PM CDT THU SEP 17 2026
KEY MESSAGES
- HIGH HEAT AND HUMIDITY WILL CONTINUE INTO EARLY THIS EVENING
OVER PORTIONS OF CENTRAL AND SOUTHEAST IL. A HEAT ADVISORY
REMAINS IN EFFECT UNTIL 7 PM SOUTH OF A SPRINGFIELD TO
ROBINSON LINE, WHERE AFTERNOON HEAT INDICES WILL PEAK NEAR 105
DEGREES.
- A BOUNDARY SLOWLY MOVING SOUTH THIS AFTERNOON WILL BE THE
FOCUS OF SHOWERS AND STORMS INTO EARLY THIS EVENING. SEVERE
WEATHER IS NOT EXPECTED BUT LOCALLY HEAVY RAINFALL IS POSSIBLE
DUE TO POTENTIAL TRAINING OF THE STORMS OVER THE SAME AREAS.
- THIS BOUNDARY WILL REMAIN NEAR THE AREA THROUGH THE WEEKEND
AND BE THE FOCUS FOR PERIODIC SHOWERS AND STORMS.
PRECIPITATION CHANCES INCREASE TO 50-80% OVER PORTIONS OF
CENTRAL ILLINOIS SATURDAY NIGHT THROUGH MONDAY AS THE BOUNDARY
FINALLY BEGINS MOVING SOUTH AND THROUGH THE AREA.
- MUCH COOLER WEATHER IS EXPECTED FOR THE MIDDLE OF NEXT WEEK AS
THE FRONT PUSHES WELL SOUTH OF THE STATE AND A CANADIAN HIGH
PRESSURE AREA BUILDS INTO THE REGION.
DISCUSSION
ISSUED AT 237 PM CDT THU SEP 17 2026
THE FRONT THAT SLOWLY MOVED SOUTH INTO THE AREA THIS MORNING
FINALLY KICKED OFF SOME ADDITIONAL SHOWERS AND STORMS OVER
SOUTHEAST ILLINOIS. THESE STORMS COULD PRODUCE LOCALLY HEAVY
RAINFALL THIS AFTERNOON INTO EARLY THIS EVENING DUE TO THE FRONT
SLOWLY MOVING AND THE STORMS TRAINING OVER THE SAME AREA. THESE
STORMS SHOULD DISSIPATE AROUND SUNSET AS THE HEATING SUBSIDES
AND THE AIRMASS BECOMES MORE STABLE.
THE HEAT AND HUMIDITY WILL ALSO CONTINUE INTO THIS EVENING,
ESPECIALLY IN AREAS NEAR AND SOUTH OF THE FRONT. THEREFORE, THE
HEAT ADVISORY REMAINS IN EFFECT UNTIL 7 PM.
THE MENTIONED BOUNDARY WILL OSCILLATE ACROSS THE CWA THE REST OF
THE WEEK AND INTO THE WEEKEND, BUT THE BETTER CHANCE OF
ADDITIONAL SHOWERS AND STORMS WILL BE ALONG AND NORTH OF
I-72/DANVILLE THROUGH FRIDAY NIGHT. THIS BOUNDARY WILL BEGIN TO
MOVE BACK SOUTH OF SATURDAY AND EVENTUALLY PUSH THROUGH THE AREA
SUNDAY NIGHT INTO MONDAY. POPS WILL BE HIGHER DURING THIS
PERIOD, REACHING 50-80% FOR SAT NIGHT THROUGH MON. HEAT AND
HUMIDITY WILL CONTINUE THROUGH THIS PERIOD AS WELL, BUT
DEWPOINTS WILL NOT BE QUITE AS HIGH AS TODAY, ONLY REACHING INTO
THE LOWER 70S, WITH UPPER 60S IN SOME AREAS. THIS WILL CAUSE
HEAT INDEX VALUES TO REMAIN BELOW 100 DEGREES FOR THE REST OF
THE WEEK AND WEEKEND.
GIVEN THE FRONT WILL BE NORTH OF MOST OF THE AREA ON SAT,
INSTABILITY WILL INCREASE TO OVER 3000 J/KG BY SAT AFTERNOON.
HOWEVER, SOME OF THE MODELS SHOW WEAK TO MARGINAL SHEAR OVER THE
AREA, SO SPC HAS MAINTAINED A MARGINAL RISK OF SEVERE WEATHER
FOR SATURDAY LATE AFTERNOON INTO SAT NIGHT. THE PRIMARY RISK
WILL BE DAMAGING WINDS AND LARGE HAIL.
BEHIND THIS WEEKEND SYSTEM, CANADIAN HIGH PRESSURE WILL BUILD
INTO THE AREA. THIS WILL BRING DRIER WEATHER TO THE AREA AND THE
BEGINNING OF COOLER TEMPERATURES. HIGHS IN THE SOUTHEAST WILL
STILL REACH INTO THE MIDDLE 80S ON MONDAY, BUT TUE INTO THU,
HIGHS WILL ONLY BE IN THE 60S AND 70S WITH LOWS IN THE 50S.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1245 PM CDT THU SEP 17 2026
ALL SITES WILL BE VFR THE REST OF THE AFTERNOON AND INTO THIS
EVENING. THEN AS WINDS BECOME STRONGER FROM THE NORTH TO
NORTHEAST, LOWER MVFR AND IFR CLOUDS WILL ADVECT INTO THE AREA
AND AFFECT THE TAFS FROM NORTH TO SOUTH. EXPECTING IFR CLOUDS AT
PIA, BMI AND CMI AT LESS THAN 1KFT, WHILE MVFR CLOUDS ARE
EXPECTED AT SPI AND DEC, AT LESS THAN 1.5KFT. THE CONDITIONS
WILL CONTINUE IN THE MORNING BUT THEN IMPROVE DURING THE LATE
MORNING HOURS AT ALL SITES. PIA, BMI, AND CMI WILL ONLY IMPROVE
TO ABOVE 1KFT BY LATE MORNING, WHILE SPI AND DEC RISE TO VFR BY
LATE MORNING. PREDOMINATE SHOWERS ARE EXPECTED AT PIA AND BMI
WITH ONLY VCSH AT SPI AND DEC. WILL LEAVE PRECIP OUT FOR CMI AS
THE PRECIP SHOULD REMAIN WELL WEST OF CMI TOMORROW. WINDS WILL
BE VARIABLE THIS AFTERNOON BUT PREDOMINATELY LESS THAN 10KTS IN
SPEED THROUGH THE PERIOD. WIND DIRECTION WILL MAINLY BE VARIABLE
OR NORTHEAST THROUGH THE PERIOD.
ILX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR ILZ049>052-061-
062-066>068-071>073.
KEY MESSAGES...AUTEN
UPDATE...AUTEN
DISCUSSION...AUTEN
AVIATION...AUTEN
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