905
FXUS63 KILX 041747
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1247 PM CDT SAT JUL 4 2026
KEY MESSAGES
- DANGEROUS HEAT AND HUMIDITY WILL CONTINUE THIS AFTERNOON,
PARTICULARLY NEAR AND SOUTH OF I-72 WHERE THERE IS A 50% TO
70% CHANCE THAT TEMPERATURES WILL REACH OR EXCEED 90F. HEAT
INDEX VALUES ARE EXPECTED TO PEAK BETWEEN 100F AND 105F FROM
I-72 SOUTH THIS AFTERNOON AND MID TO UPPER 90S NORTH OF I-72.
- A BAND OF THUNDERSTORMS IS EXPECTED TO DEVELOP OVER WEST
CENTRAL IL DURING MIDDAY/EARLY AFTERNOON AND TRACK EASTWARD
ACROSS CENTRAL AND SOUTHEAST IL DURING MID AFTERNOON INTO
EARLY EVENING (60-80% CHANCE). THERE IS A SLIGHT CHANCE OF
SEVERE STORMS THIS AFTERNOON AND EARLY EVENING OVER MUCH OF
CENTRAL AND SOUTHEAST IL, WITH DAMAGING WINDS THE PRIMARY
SEVERE WEATHER THREAT ALONG WITH LOCALIZED TORRENTIAL RAINFALL
OF 1-3 INCHES THAT COULD LEAD TO MINOR FLOODING ESPECIALLY IN
URBAN AREAS.
- A REFRESHING BREAK FROM THE HEAT ARRIVES EARLY NEXT WEEK.
FOLLOWING A FINAL ROUND OF SCATTERED SHOWERS ON SUNDAY, A COLD
FRONT WILL BRING A STRETCH OF DRY AND COMFORTABLE WEATHER WITH
HIGHS IN THE MID-80S FROM MONDAY THROUGH WEDNESDAY.
UPDATE
ISSUED AT 1045 AM CDT SAT JUL 4 2026
UPDATED THE FORECAST TODAY AND EVENING FOR TIMING AND COVERAGE
OF THUNDERSTORMS THIS AFTERNOON INTO THIS EVENING OVER CENTRAL
AND SOUTHEAST IL. SPC DAY1 UPDATE HAS UPGRADED TO A SLIGHT RISK
OF SEVERE STORMS THIS AFTERNOON AND EVENING OVER MUCH OF CWA
(EXCLUDING KNOX AND STARK COUNTIES WHICH ARE STILL IN A MARGINAL
RISK OF SEVERE). THERE IS A 15% RISK OF DAMAGING WINDS AND
LOCALLY HEAVY RAINS WITH A FEW SPOTS THAT COULD GET 1-3 INCHES
OF RAIN IN 1-2 HOURS THAT COULD LEAD TO POSSIBLE FLOODING
ESPECIALLY IN URBAN AREAS AS WE EXPERIENCED IN DECATUR AND FLORA
LAST NIGHT. MUCAPES ELEVATED TO 2000-3500 J/KG BY EARLY
AFTERNOON WHILE EFFECTIVE BULK SHEAR VALUES ARE GENERALLY LESS
THAN 25 KTS, BUT COULD GET HIGHER WITH MCV APPROACHING FROM
NORTHWEST MO. THE MCV WILL LIKELY IMPACT CENTRAL IL DURING
MID/LATE AFTERNOON WITH A PERIOD OF LIKELY CHANCES OF
THUNDERSTORMS AND POSSIBLE SEVERE STORMS. HIGHER CHANCES OF
CONVECTION SHIFT INTO SE IL DURING THIS EVENING AFTER 7 PM. WE
ALSO HAVE A HEAT ADVISORY IN EFFECT THROUGH 7 PM FOR ALL OF CWA
EXCEPT KNOX, STARK AND MARSHALL COUNTIES. CURRENTLY HEAT INDICES
ARE IN THE UPPER 80S AND LOWER 90S AND PROJECTED TO RISE ANOTHER
10 DEGREES BY EARLY/MID AFTERNOON AHEAD OF THE STORMS. THE
HIGHEST TEMPS NEAR 90F OR LOWER 90S IS FROM I-72 SOUTH WHERE
HEAT INDICES PEAK AT 100-105F. HIGHS IN THE UPPER 80S NORTHERN
CWA WHERE HEAT INDICES REACH MID TO UPPER 90S. WEAK LONG
DURATION OF HEAT WAVE THAT STARTED SUNDAY JUNE 28TH SUPPORTS
HEAT ADVISORY HEADLINE, THOUGH MAY BE ABLE TO END IT EARLY AFTER
STORMS ROLL THROUGH ESPECIALLY NORTH OF I-70.
DISCUSSION
ISSUED AT 253 AM CDT SAT JUL 4 2026
HEAT AND HUMIDITY
CENTRAL ILLINOIS STARTS THIS MORNING NOTICEABLY COOLER AND MORE
STABLE THAN PREVIOUS DAYS, COURTESY OF WIDESPREAD NOCTURNAL
CONVECTION. THE PRIMARY FORECASTING CHALLENGE REVOLVES AROUND
HOW EFFICIENTLY THE BOUNDARY LAYER CAN MIX OUT THIS STABLE
AIRMASS. GIVEN THE HIGH JULY SUN ANGLE, ANY BRIEF WINDOWS OF
CLEARING BY EARLY AFTERNOON WILL PROMOTE RAPID BOUNDARY LAYER
RECOVERY. THE LATEST HREF GUIDANCE POINTS TO THE HIGHEST
PROBABILITY (40-60% CHANCE) OF TEMPERATURES EXCEEDING 90F NEAR
AND SOUTH OF THE INTERSTATE 70 CORRIDOR. THIS ALIGNS WELL WITH
RECENT OBSERVATIONAL TRENDS; INFRARED SATELLITE AND RADAR
IMAGERY SHOW CONVECTIVE OUTFLOWS STALLING OUT IN THE VICINITY OF
I-70. CONSEQUENTLY, THIS CORRIDOR REPRESENTS THE GREATEST RISK
FOR ADVISORY-LEVEL HEAT INDEX VALUES RANGING FROM 100F TO 105F
THIS AFTERNOON. WHILE HEAT INDEX VALUES OF 95F TO 100F MAY BE
MORE COMMON NORTH OF I-70, THE CURRENT HEAT ADVISORY WILL BE
MAINTAINED IN FULL TO ACCOUNT FOR THE POSSIBILITY OF A MORE
AGGRESSIVE MIDDAY RECOVERY.
SEVERE AND HEAVY RAINFALL POTENTIAL
CONFIDENCE IN WIDESPREAD AFTERNOON CONVECTION HAS RISEN BASED
ON OVERNIGHT UPSTREAM TRENDS. MULTIPLE MESOSCALE CONVECTIVE
SYSTEMS (MCSS) WILL CONTINUE TRACKING EASTWARD THIS MORNING
WITHIN A CHAOTIC, ZONAL FLOW REGIME, GRADUALLY DECAYING WITH
EASTWARD EXTENT. BY EARLY AFTERNOON, MULTIPLE MESOSCALE
CONVECTIVE VORTICES (MCVS) EMBEDDED WITHIN A CONVECTIVELY-
AUGMENTED SHORTWAVE WILL CROSS THE MID-MISSISSIPPI VALLEY,
PROVIDING THE NECESSARY SYNOPTIC ASCENT TO IGNITE WIDESPREAD
THUNDERSTORM ACTIVITY ACROSS CENTRAL ILLINOIS.
AS THE BOUNDARY LAYER RECOVERS TODAY, TEMPERATURES CLIMBING
INTO THE MID-TO-UPPER 80S ALONGSIDE RICH DEWPOINTS IN THE LOW-
TO-MID 70S WILL YIELD 2,500 TO 3,000 J/KG OF MLCAPE. WHILE THE
THERMODYNAMIC PARAMETER SPACE IS ROBUST, IT WILL ONCE AGAIN BE
UNDERCUT BY WEAK KINEMATIC PROFILES, FEATURING DEEP-LAYER BULK
SHEAR GENERALLY AT OR BELOW 20 KNOTS. HOWEVER, THE APPROACHING
SHORTWAVE COULD LOCALLY ENHANCE DEEP-LAYER SHEAR UP TOWARD 30
KNOTS.
WIDESPREAD, ORGANIZED SEVERE WEATHER IS NOT ANTICIPATED. INSTEAD,
WITHIN A HIGH-PWAT AIRMASS, HIGH PRECIPITATION EFFICIENCY WILL
FAVOR PULSE CONVECTION OR TRANSIENT, DISORGANIZED CLUSTERS. THE
PRIMARY HAZARDS WITH THIS ACTIVITY WILL BE LOCALIZED TORRENTIAL
DOWNPOURS AND WET MICROBURSTS CAPABLE OF ISOLATED WIND DAMAGE.
CONVECTIVE ACTIVITY IS EXPECTED TO TAPER OFF FROM WEST TO EAST
BY MID-TO-LATE EVENING AS SUBSIDENCE BUILDS IN BEHIND THE
DEPARTING MCVS AND SHORTWAVE. GIVEN THE ABSENCE OF A
STRENGTHENING LOW-LEVEL JET (LLJ), STORMS SHOULD STRUGGLE TO
FESTER PAST 9-10 PM.
NEXT WEEK
BY MIDDAY SUNDAY, THE PRIMARY UPPER-LEVEL SHORTWAVE TROUGH AXIS
WILL BEGIN CROSSING THE REGION, DRAGGING AN ATTENDANT SURFACE
COLD FRONT THROUGH CENTRAL ILLINOIS. BECAUSE AIRMASS RECOVERY
OCCURS READILY THIS TIME OF YEAR, BOUNDARY LAYER CONDITIONS
AHEAD OF THE FRONT APPEAR FAVORABLE ENOUGH TO SUPPORT ANOTHER
ROUND OF SCATTERED THUNDERSTORMS ON SUNDAY AFTERNOON.
THE PASSAGE OF THIS COLD FRONT WILL EFFECTIVELY SCOUR OUT THE
MULTI-DAY TROPICAL AIRMASS. DEWPOINTS ARE FORECAST TO DROP BACK
INTO THE MUCH MORE COMFORTABLE MID-60S TO LOWER 70S BY MONDAY.
A WELCOME STRETCH OF SEASONABLE AND DRY WEATHER IS ANTICIPATED
FROM MONDAY THROUGH WEDNESDAY AS A TRANSIENT SHORTWAVE RIDGE
BUILDS ACROSS THE MIDWEST. EXPECT DAYTIME HIGHS TO HOVER
COMFORTABLY IN THE MID-80S DURING THIS PERIOD.
THE MIDWEEK RESPITE LOOKS TO BE SHORT-LIVED. LONG-RANGE GUIDANCE
HINTS AT A RETURN TO UNSETTLED WEATHER BY LATE NEXT WEEK AS A
WELL- DEFINED TROUGH IS PROJECTED TO DIG ACROSS THE UPPER
MIDWEST. THIS SYSTEM WILL DRAG ANOTHER COLD FRONT INTO THE
REGION, WHICH IS MODELED TO STALL SOMEWHERE OVER THE STATE. THIS
SETUP WILL REINTRODUCE DAILY CHANCES FOR SHOWERS AND
THUNDERSTORMS HEADING INTO THE WEEKEND.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1245 PM CDT SAT JUL 4 2026
EXPECT SCATTERED TO BROKEN BANDS OF CONVECTION TO DEVELOP AND
SPREAD EASTWARD ACROSS CENTRAL IL DURING THIS AFTERNOON. A FEW
ISOLATED THUNDERSTORMS HAVE DEVELOPED IN PAST HOUR WEST OF I-57
AND TRACKING SLOWLY ENE AT 15 MPH. WE CARRIED TEMPO GROUPS FOR
AROUND 3 HOURS FOR MVFR CONDITIONS FOR THUNDERSTORMS AND COULD
SEE WIND GUSTS OVER 40 KTS WITH STRONGER STORMS. BRUNT OF
CONVECTION TO PASS SE OF CENTRAL IL AIRPORTS AFTER 23-24Z WITH
ISOLATED CONVECTION POSSIBLE FOR A FEW HOURS UNTIL DUSK. HRRR IS
SHOWING MVFR CEILINGS AND POSSIBLE VSBYS WITH FOG DEVELOPING
OVERNIGHT AFTER 06-08Z ESPECIALLY ALONG I-74. IF THESE MVFR
CONDITIONS DEVELOP, EXPECTED THEM TO LIFT TO VFR BETWEEN 14-15Z
SUNDAY MORNING. SW WINDS OF 5-10 KTS EARLY THIS AFTERNOON TO
SWITCH WEST TO NW LATER THIS AFTERNOON AND EVENING, AND VEER
MORE NORTHERLY DURING TONIGHT INTO SUNDAY MORNING.
ILX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR ILZ029-031-
036>038-040>057-061>063-066>068-071>073.
KEY MESSAGES...MJA
UPDATE...07
DISCUSSION...MJA
AVIATION...07
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