531
FXUS63 KILX 312305
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
605 PM CDT MON AUG 31 2026
KEY MESSAGES
- HEAT INDEX VALUES BETWEEN 100 AND 105+ DEGREES ARE EXPECTED
TUESDAY THROUGH THURSDAY. THERE IS A HIGH CHANCE (>60%) OF
HEAT INDEX VALUES EXCEEDING 100 DEGREES SOUTH OF A LINE FROM
BEARDSTOWN TO TERRE HAUTE ON TUESDAY, EXPANDING TO AREAS SOUTH
OF INTERSTATE 74 ON WEDNESDAY.
- MORE SEASONAL CONDITIONS ARRIVE BY LATE WEEKEND, LOWERING
HIGH TEMPERATURES INTO THE MID-80S BEHIND A SLOW MOVING COLD
FRONT. THE PASSING COLD FRONT BRINGS A LOW (20%) CHANCE OF
SHOWERS AND THUNDERSTORMS FRIDAY AND SATURDAY.
DISCUSSION
ISSUED AT 113 PM CDT MON AUG 31 2026
LATE SUMMER HEAT WAVE
UPPER-LEVEL RIDGING REMAINS DOMINANT ACROSS THE MIDWEST THIS
WEEK, SUPPORTED BY A ROBUST NEARLY 600 DAM 500MB HIGH CENTERED
OVER THE MID-MISSISSIPPI AND TENNESSEE VALLEYS THROUGH
WEDNESDAY. THE RIDGE AXIS IS PROGGED TO SHIFT TOWARD THE MID-
ATLANTIC COAST BY LATE WEEK. UNDER THIS SUBSIDENCE, TEMPERATURES
WILL REMAIN WELL ABOVE SEASONAL NORMALS THROUGH THE REMAINDER
OF THE WEEK WITH MOST PRECIPITATION BYPASSING THE LOCAL AREA TO
THE NORTH, THOUGH PERIODIC CONVECTIVE THREATS MAY CLIP CENTRAL
ILLINOIS.
SURFACE ANALYSIS THIS AFTERNOON SHOWS RIDGING ALONG THE
APPALACHIANS WITH LOW PRESSURE OVER THE CANADIAN PRAIRIES,
MAINTAINING A SOUTHWESTERLY GRADIENT ACROSS CENTRAL ILLINOIS AND
PUSHING AMBIENT TEMPERATURES INTO THE LOW TO MID-90S. DEW POINT
FORECASTING REMAINS CHALLENGING AS MOISTURE ADVECTION IS
TEMPERED BY DEEP MIXING INTO A VERY DRY COLUMN. CURRENT DEW
POINTS IN THE MID-60S TO LOWER 70S ARE YIELDING HEAT INDICES
NEAR 100 DEGREES.
SIMILAR CONDITIONS ARE EXPECTED TUESDAY AND WEDNESDAY, WITH AN
ADDITIONAL UPTICK IN TEMPERATURES AS THE 850MB THERMAL RIDGE
PEAKS BETWEEN 24-27C -- VALUES EXCEEDING THE 90TH PERCENTILE OF
CLIMATOLOGY. SURFACE HIGHS WILL REACH THE MID TO UPPER 90S,
DRIVING PEAK HEAT INDICES INTO THE 100-105+ RANGE. LREF
PROBABILITIES FOR HEAT INDICES >100 DEGREES ARE HIGH (>60%),
FOCUSED SOUTH OF A BEARDSTOWN TO TERRE HAUTE LINE ON TUESDAY AND
EXPANDING SOUTH OF I-74 ON WEDNESDAY. IN COLLABORATION WITH
NEIGHBORING OFFICES, THE HEAT ADVISORY WAS EXPANDED TO THE
REMAINDER OF THE CENTRAL ILLINOIS COUNTIES TUESDAY THROUGH
THURSDAY.
SLOW PATTERN CHANGE LATE WEEK AND WEEKEND
A STRONG SHORTWAVE TROUGH WILL DIG ACROSS THE GREAT LAKES
WEDNESDAY NIGHT AND THURSDAY, FOLLOWED BY A MORE POTENT WAVE
OVER THE WEEKEND. THIS WILL SHUNT THE PRIMARY UPPER RIDGE AXIS
BACK OVER THE GREAT PLAINS, TRANSITIONING CENTRAL ILLINOIS INTO
A NORTHWEST FLOW REGIME. AT THE SURFACE, CANADIAN HIGH PRESSURE
BUILDING ACROSS QUEBEC WILL DRIVE A BACKDOOR COLD FRONT THROUGH
ILLINOIS. THIS BOUNDARY WILL SERVE AS THE FOCUS FOR SLIGHT
CHANCE POPS (20%) FRIDAY AND SATURDAY. TEMPERATURES WILL
MODERATE FROM THE 90S AHEAD OF THE FRONT THURSDAY AND FRIDAY TO
THE MID-80S IN ITS WAKE FOR AT LEAST PARTS OF THE AREA SUNDAY.
THE CURRENT HEAT ADVISORY MAY REQUIRE EXTENSION FOR PORTIONS OF
THE AREA DEPENDING ON THE EVENTUAL FRONTAL SPEED AND
PRECIPITATION COVERAGE.
AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 605 PM CDT MON AUG 31 2026
SOUTH TO SOUTHWEST WINDS EXPECTED TO CONTINUE THROUGH THE
PERIOD, BUT OVERALL SHOULD BE A BIT LIGHTER ON WEDNESDAY THAN
THEY WERE TODAY. VFR CONDITIONS WILL PREVAIL, WITH ANY HIGH
CLOUD COVER MAINLY LIMITED TO AREAS NORTH OF KBMI/KPIA.,
CLIMATE
ISSUED AT 440 PM CDT MON AUG 31 2026
RECORD HIGH TEMPERATURES THIS WEEK:
LOCATION TUE 9/1 WED 9/2 THU 9/3
======== ======== ======== ========
BLOOMINGTON 102/1894 101/2011 102/1913
CHAMPAIGN 102/2011 101/2011 99/2011
CHARLESTON 99/2011 103/1953 100/1925
DANVILLE 101/1953 101/1953 99/1913
DECATUR 102/1953 102/1953 102/1913
JACKSONVILLE 103/1913 103/2011 101/2011
LINCOLN 102/1953 101/1953 100/1913
OLNEY 105/1953 106/1953 105/1925
PARIS 101/1953 102/1953 101/1913
PEORIA 101/1913 100/1913 99/1913
SPRINGFIELD 102/2011 101/2011 100/2011
ILX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY UNTIL 7 PM CDT THURSDAY FOR ILZ027>029-036-037-
040>044-047>056-061>063-066>068-071>073.
HEAT ADVISORY FROM 1 PM TUESDAY TO 7 PM CDT THURSDAY FOR
ILZ030-031-038-045-046-057.
KEY MESSAGES...DEUBELBEISS
DISCUSSION...DEUBELBEISS
AVIATION...GEELHART
CLIMATE...GEELHART
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