170
FXUS63 KILX 262343
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
225 PM CDT SAT JUL 26 2025
KEY MESSAGES
- A MEDIUM PROBABILITY (15-40% CHANCE) OF FLASH FLOODING EXISTS
TODAY AND TONIGHT. A FLASH FLOOD WATCH IS NOW IN EFFECT FOR
PORTIONS OF CENTRAL ILLINOIS WHERE AN ADDITIONAL 1 AND 4 INCHES
OF RAINFALL IS FORECAST.
- A HEAT ADVISORY IS IN EFFECT ALONG AND SOUTH OF A JACKSONVILLE
TO DANVILLE LINE TODAY. THE OPPRESSIVE HEAT WILL SPREAD BACK
NORTHWARD ACROSS ALL OF CENTRAL ILLINOIS SUNDAY THROUGH TUESDAY
AS HEAT INDEX VALUES ONCE AGAIN REACH 105-115.
- A LOW PROBABILITY (5-15% CHANCE) OF SEVERE WEATHER EXISTS NORTH
OF THE I-70 CORRIDOR TODAY...WITH THE PRIMARY RISKS BEING
SCATTERED DAMAGING WIND GUSTS AND LARGE HAIL.
DISCUSSION
(THROUGH NEXT FRIDAY NIGHT)
ISSUED AT 1246 PM CDT SAT JUL 26 2025
RADAR AND SATELLITE ANALYSES SHOW A DECAYING MESOSCALE CONVECTIVE
VORTEX (MCV) MOVING ACROSS NORTHERN ILLINOIS, WITH TWO OUTFLOW
BOUNDARIES PUSHING SOUTH ACROSS CENTRAL ILLINOIS. THESE
BOUNDARIES HAVE MOSTLY CONVERGED AND ERODED NEAR A LINE EXTENDING
FROM ROUGHLY JACKSONVILLE TO GIBSON CITY. NORTH OF THIS BOUNDARY,
CONDITIONS MAY REMAIN STABLE ENOUGH TO PREVENT NEW CONVECTIVE
DEVELOPMENT THIS AFTERNOON. NEAR AND SOUTH OF THE BOUNDARY,
CAPE/SHEAR PROFILES ARE SUPPORTIVE OF STRONG-TO-SEVERE STORMS AND
THE POTENTIAL FOR URBAN AND SMALL STREAM FLOODING.
MANY AREAS IN WEST-CENTRAL AND NORTH-CENTRAL ILLINOIS HAVE ALREADY
RECEIVED MULTIPLE INCHES OF RAINFALL IN THE PAST 24 HOURS, WITH
RATES EXCEEDING 1-2 INCHES PER HOUR. GIVEN A SIMILAR AIR MASS NEAR
AND SOUTH OF THE RESIDUAL OUTFLOW THIS AFTERNOON, ADDITIONAL HEAVY
RAINFALL POCKETS ARE ANTICIPATED INTO THIS EVENING ACROSS PORTIONS
OF CENTRAL AND SOUTHEAST ILLINOIS.
OTHERWISE, THE DANGEROUS HEAT HAS CONTINUED INTO THIS AFTERNOON,
WITH AREAS WITHIN THE HEAT ADVISORY ALREADY DISPLAYING HEAT INDEX
VALUES BETWEEN 97-107 F EVEN DESPITE INCREASING CLOUD COVER.
BY SUNDAY, A ROBUST HEAT DOME WILL EXTEND NORTHWARD INTO CENTRAL
ILLINOIS, SHIFTING THE EFFECTIVE SURFACE BOUNDARY OUT OF OUR AREA
AND REDUCING UPPER-LEVEL FLOW AND DEEP-LAYER SHEAR. WHILE BOUNDARY
LAYER CONDITIONS WILL REMAIN MODERATELY UNSTABLE SUNDAY AFTERNOON,
ESPECIALLY NEAR AND SOUTH OF THE I-72/DANVILLE CORRIDOR, WITHIN A
WIDE AREA OF VERY HIGH PWATS (> 2 INCHES), THE POOR DEEP-LAYER
SHEAR SUGGESTS SOMEWHAT LIMITED CONVECTIVE COVERAGE AND INTENSITY.
THE PRIMARY CONCERN WILL BE TORRENTIAL RAINFALL FROM ANY
DEVELOPING MULTI-CELL CLUSTERS IN THE VICINITY OF A REMNANT
OUTFLOW, WHEREVER IT EVOLVES.
OUR POSTURE ON HEAT HEADLINES HAVE LARGELY REMAINED UNCHANGED,
WITH THE CURRENT HEAT ADVISORY MOST LIKELY NEEDING AN
EXTENSION/EXPANSION ACROSS THE REGION THROUGH WEDNESDAY. WHILE
FORECAST GUIDANCE HAS PERSISTENTLY HIGHLIGHTED MONDAY AND TUESDAY
AS THE HOTTEST DAYS OF THE PERIOD, SOME CONCERN LINGERS REGARDING
THE EVOLUTION OF UPSTREAM CONVECTION EACH OF THOSE DAYS. THIS
POTENTIAL HAS COME INTO BETTER FOCUS WITH THIS MORNING'S SUITE OF HI-
RES GUIDANCE, WHERE ALL OF THE HRRR, 3KM NAM, ARW, AND FV3 ALL
DEPICT DECAYING CONVECTION ENTERING NORTHERN/CENTRAL PORTIONS OF
ILLINOIS BY MONDAY MORNING. THIS CONVECTIVE DEBRIS COULD BE ENOUGH
TO THWART AN UPGRADE TO AN EXTREME HEAT WARNING ON MONDAY, AT LEAST
FOR A GOOD CHUNK OF OUR AREA. AS A RESULT, WE WILL LIKELY TAKE A
MORE CONSERVATIVE DAY-TO-DAY APPROACH WITH HEAT HEADLINES, EXTENDING
AND EXPANDING THE CURRENT HEAT ADVISORY AS NEEDED BASED ON TRENDS.
A MAJOR PATTERN CHANGE STILL LOOKS ON TRACK TO OCCUR WEDNESDAY
INTO THURSDAY, WITH SIGNIFICANTLY COOLER AND DRIER CONDITIONS
FORECAST BY THE BACK HALF OF NEXT WEEK.
MJA
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1221 PM CDT SAT JUL 26 2025
THE MAIN AVIATION FORECAST CONCERN IS FOR PERIODS OF HEAVY SHOWERS
AND THUNDERSTORMS TO DEVELOP THIS AFTERNOON, WITH THE POTENTIAL
FOR THEM TO PERSIST THROUGH MUCH OF THE EVENING HOURS,
PARTICULARLY NEAR AND JUST EAST OF THE INTERSTATE 55 TERMINALS.
WITH RECENT SATELLITE TRENDS ALREADY SHOWING GROWING CUMULUS
DEVELOPING ACROSS CENTRAL ILLINOIS, HAVE DECIDED TO INTRODUCE A
TEMPO GROUP FOR TSRA THIS AFTERNOON ACROSS THE BOARD BETWEEN
18-22Z, WITH THE FOCUS BEING NEAR THE KSPI/KDEC/KBMI TERMINALS
INTO THIS EVENING. CONFIDENCE AND COVERAGE ARE BOTH LOWER THIS
EVENING, AND HAVE THEREFORE PROCEEDED WITH A PROB30 GROUP FOR TSRA
THAT SPANS THE LATE EVENING PERIOD.
WINDS WILL MAINLY BE FROM THE SOUTHWEST AROUND 10 KTS, THOUGH WE
WILL NEED TO MONITOR FOR ABRUPT CHANGES IN SPEED AND DIRECTION DUE
TO THUNDERSTORM OUTFLOW.
MJA
ILX WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH UNTIL 7 PM CDT THIS EVENING FOR ILZ027-028-030.
HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR ILZ049>057-061>063-
066>068-071>073.
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