927
FXUS63 KILX 041048
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
548 AM CDT SAT JUL 4 2026
KEY MESSAGES
- DANGEROUS HEAT AND HUMIDITY WILL CONTINUE THIS AFTERNOON,
PARTICULARLY NEAR AND SOUTH OF INTERSTATE 70 WHERE THERE IS A
40% TO 60% CHANCE THAT TEMPERATURES WILL EXCEED 90F. HEAT
INDEX VALUES IN THIS SOUTHERN CORRIDOR ARE EXPECTED TO PEAK
BETWEEN 100F AND 105F.
- WIDESPREAD THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS
AFTERNOON AND EVENING ACROSS CENTRAL ILLINOIS (60-80% CHANCE).
WHILE ORGANIZED SEVERE WEATHER IS UNLIKELY, ANY STORM COULD
PRODUCE LOCALIZED TORRENTIAL RAINFALL LEADING TO MINOR
FLOODING, AS WELL AS ISOLATED DAMAGING WIND GUSTS.
- 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.
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 /12Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 538 AM CDT SAT JUL 4 2026
WIDESPREAD THUNDERSTORM ACTIVITY IS PROJECTED TO RETURN ACROSS
THE REGION THIS AFTERNOON AND EVENING, PRIMARILY BETWEEN
18Z-00Z. CONFIDENCE HAS NOW INCREASED ENOUGH TO COVER THIS
POTENTIAL WITH A TEMPO GROUP, THOUGH COVERAGE REMAINS JUST
LIMITED ENOUGH TO PRECLUDE A PREDOMINANT TSRA MENTION.
BEYOND THE IMMEDIATE INFLUENCE OF STORM ACTIVITY, AMBIENT WIND
SPEEDS ARE MODELED TO REMAIN UNDER 10 KTS. NEVERTHELESS, ROBUST
LOCALIZED THUNDERSTORMS WILL LIKELY INTRODUCE CHAOTIC
DISRUPTIONS TO THE REGIONAL WIND FIELD, RESULTING IN HIGHLY
VARIABLE SURFACE WIND DIRECTIONS THROUGH THE PERIOD.
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
DISCUSSION...MJA
AVIATION...MJA
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