963
FXUS63 KILX 181733
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1233 PM CDT SAT JUL 18 2026
KEY MESSAGES
- CONDITIONS ARE FAVORABLE FOR LOCALIZED DAMAGING WIND GUSTS
WITH THUNDERSTORMS THIS AFTERNOON AND EVENING, WITH CHANCES
GREATEST NORTH OF A LINE FROM GALESBURG TO MATTOON-CHARLESTON.
- WARM TEMPERATURES AND HIGH HUMIDITY WILL RESULT IN HEAT INDEX
VALUES FROM 100 TO 105 DEGREES THIS AFTERNOON. PORTIONS OF
CENTRAL ILLINOIS MAY EXPERIENCE SIMILAR CONDITIONS ON MONDAY
AND TUESDAY.
- WILDFIRE SMOKE WILL BEGIN MOVING INTO CENTRAL ILLINOIS FROM
THE NORTH EARLY SUNDAY MORNING. MOST OF THE AREA WILL LIKELY
BE AFFECTED BY SUNDAY AFTERNOON.
DISCUSSION
ISSUED AT 253 AM CDT SAT JUL 18 2026
*** SEVERE STORM POTENTIAL THIS AFTERNOON/EVENING ***
A COLD FRONT CONNECTED TO A SURFACE LOW MOVING ACROSS SOUTHWEST
ONTARIO/SOUTHEAST QUEBEC WILL MOVE INTO ILLINOIS LATER THIS
MORNING, AND BECOME A FOCUS FOR THUNDERSTORM DEVELOPMENT THIS
AFTERNOON. THOUGH 0-6 KM SHEAR IS FORECAST TO BE IN THE 15-25
KT RANGE WHICH MAY LIMIT STORM ORGANIZATION, SEVERAL PARAMETERS
WILL BE FAVORABLE FOR LOCALIZED DOWNBURST POTENTIAL. MLCAPE
VALUES ARE FORECAST TO BE NEAR 3000 J/KG IN A THIN STRIPE JUST
AHEAD OF THE COLD FRONT. IN ADDITION, DCAPE VALUES IN THE
1100-1300 J/KG RANGE JUST AHEAD OF THE FRONT WILL SUPPORT STRONG
RAIN-COOLED DOWNDRAFTS. THE 00Z HRRR INDICATES MULTIPLE POCKETS
OF NEAR-SEVERE WIND GUSTS IN THE 4 PM - 8 PM TIME FRAME, WITH
THE GREATEST COVERAGE OF STRONG WIND GUSTS NORTH OF A LINE FROM
GALESBURG TO MATTOON-CHARLESTON. STORMS SHOULD EXIT THE FORECAST
AREA AND DECREASE NOTABLY IN COVERAGE BY AROUND MIDNIGHT
TONIGHT.
*** HIGH HEAT INDEX VALUES THIS AFTERNOON AND EARLY NEXT WEEK ***
CURRENT FORECASTS SUPPORT HEAT INDEX VALUES THIS AFTERNOON
LARGELY IN THE 100 TO 105 DEGREE RANGE. THERE IS SOME SPREAD IN
SHORT-TERM MODEL FORECASTS OF TEMPERATURE AND MOISTURE, WITH THE
HRRR INDICATING SOME MIXING OUT OF DEWPOINTS INTO THE UPPER 60S
AHEAD OF THE FRONT THIS AFTERNOON. WESTERLY WINDS AROUND 10
KNOTS AHEAD OF THE FRONT, WITH CURRENT UPSTREAM DEWPOINTS
MODESTLY LOWER, MAY LEND SOME SUPPORT TO THE IDEA OF TEMPERING
THE DAYTIME RISE IN NEAR-SURFACE MOISTURE BUT THE AFFECT WILL
PROBABLY BE LIMITED AND NOT AS DRAMATIC AS THE HRRR INDICATES.
GOING WITH A BLEND OF INPUTS PLACES HEAT INDICES TODAY IN A
SIMILAR RANGE TO THOSE OBSERVED YESTERDAY. THERE IS A 20-30%
CHANCE OF HEAT INDEX VALUES EXCEEDING THE 105 DEGREE THRESHOLD
THIS AFTERNOON, MOSTLY WEST OF I-55. ONCE CONVECTION DEVELOPS
AND PRODUCES DOWNDRAFTS/OUTFLOW, THE HEAT INDEX VALUES SHOULD
DECREASE FROM NORTH TO SOUTH.
FOLLOWING A COOLER DAY IN THE POST-FRONTAL AIRMASS ON SUNDAY,
TEMPERATURES WILL WARM AGAIN ON MONDAY. AS WINDS TURN BACK TO
SOUTHERLY IN RESPONSE TO THE NEXT SHORT-WAVE TROUGH,
TEMPERATURES WILL WARM MOST QUICKLY WEST OF THE ILLINOIS RIVER.
COMBINED WITH HIGH HUMIDITY, HEAT INDEX VALUES WILL AGAIN BE IN
THE 100 TO 105 DEGREE RANGE. AS THE NEXT COLD FRONT MOVES
THROUGH ON TUESDAY, SOUTHERN PORTIONS OF THE AREA WILL RETAIN
THE HEAT THE LONGEST WITH HIGH HEAT INDICES PERSISTING ROUGHLY SOUTH
OF I-70.
*** WILDFIRE SMOKE SUNDAY ***'
SMOKE FROM WILDFIRES TO THE NORTH IS ANTICIPATED TO HEAD BACK
TOWARD ILLINOIS AS THE POST-FRONTAL SURFACE HIGH SETTLES
SOUTHWARD ON SUNDAY. SMOKE TRANSPORT MODELS BRING THE SMOKE INTO
NORTHERN PORTIONS OF THE FORECAST AREA AROUND SUNRISE SUNDAY
MORNING, POTENTIALLY AFFECTING MUCH OF CENTRAL AND SOUTHEAST
ILLINOIS BY LATE SUNDAY AFTERNOON. THERE ARE DIFFERENCES BETWEEN
THE SMOKE FORECASTS FROM THE HRRR AND RRFS, WITH THE
CONCENTRATION BEING MUCH LESS IN THE HRRR. IT IS WORTH NOTING
THAT EVEN IF THE GREATER CONCENTRATION FORECAST BY THE RRFS IS
REALIZED, WE ARE NOT ANTICIPATING THE DEGREE OF SMOKE
EXPERIENCED BY THOSE IN NORTHEASTERN ILLINOIS YESTERDAY. CURRENT
AIR QUALITY FORECASTS ARE IN THE MODERATE CATEGORY FOR TOMORROW.
SHOULD GREATER IMPACTS DEVELOP, THEY WOULD MOST LIKELY BE IN AN
AREA NORTHEAST OF A LINE FROM GALESBURG TO EFFINGHAM.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1213 PM CDT SAT JUL 18 2026
A SLOW MOVING COLD FRONT WILL SAG SOUTH ACROSS CENTRAL ILLINOIS
LATE THIS AFTERNOON AND EVENING. SCATTERED THUNDERSTORMS ARE
EXPECTED ALONG THE FRONT, SOME OF WHICH COULD BE STRONG TO
SEVERE. WESTERLY WINDS AHEAD OF THE FRONT WILL VEER TO NORTHWEST
THEN NORTHEAST IN ITS WAKE. AS WINDS TURN NORTHEASTERLY
OVERNIGHT, SMOKE FROM CANADIAN WILDFIRES IS EXPECTED TO
OVERSPREAD THE AREA. CONFIDENCE IS LOW IN ANY IMPACTS TO
VISIBILITY BUT UPSTREAM OBS WILL NEED TO BE CLOSELY MONITORED AS
SMOKE APPROACHES CENTRAL ILLINOIS.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...AAT
DISCUSSION...AAT
AVIATION...DEUBELBEISS
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