811
FXUS63 KILX 271754
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1254 PM CDT SAT JUN 27 2026
KEY MESSAGES
- A MARGINAL RISK OF SEVERE THUNDERSTORMS AND LOCALIZED HEAVY
RAINFALL EXISTS SOUTH OF INTERSTATE 70 THIS AFTERNOON, WHILE A
STALLED FRONT SOUTH OF INTERSTATE 72 PRESENTS A RISK FOR FUNNEL
CLOUDS.
- AN EXTENDED PERIOD OF DANGEROUS HEAT AND HUMIDITY BEGINS
SUNDAY, WITH A HEAT ADVISORY ACTIVE AND LIKELY REQUIRING
EXTENSIONS THROUGH MUCH OF THE UPCOMING WORKWEEK.
- DRY CONDITIONS DOMINATE THROUGH MIDWEEK BEFORE THUNDERSTORM
CHANCES RETURN LATE NEXT WEEK.
DISCUSSION
ISSUED AT 1254 PM CDT SAT JUN 27 2026
CURRENT SURFACE ANALYSIS REVEALS A WEAK, STALLED FRONTAL
BOUNDARY POSITIONED JUST SOUTH OF THE INTERSTATE 72 CORRIDOR.
HIGH-RESOLUTION CONVECTIVE GUIDANCE INDICATES AN ENVIRONMENT
CHARACTERIZED BY LOCALIZED LOW-LEVEL VORTICITY AND WEAK
VERTICAL SHEAR ALONG THIS BOUNDARY. THE NON-SUPERCELL TORNADO
PARAMETER (NSTP) HIGHLIGHTS VALUES BETWEEN 2 AND 4, WHICH
JUSTIFIES A MENTION OF FUNNEL CLOUDS STRETCHED ALONG A
JACKSONVILLE TO PARIS CORRIDOR THROUGH THIS AFTERNOON (SEE
RECENTLY ISSUED SPECIAL WEATHER STATEMENT). IN FACT, A BRIEF
FUNNEL WAS REPORTED AT NOON SOUTH OF DECATUR. IF ENOUGH CLOUD
BREAKS CAN BE SUSTAINED, AN INCREASE IN LOW LEVEL LAPSE RATES
PAIRED WITH LOW LCLS WOULD MAKE A FEW LANDSPOUT TORNADOES
POSSIBLE, THOUGH HIGHER BOUNDARY LAYER FRICTION DUE TO CROP
HEIGHT MAKE THIS LESS LIKELY THAN A MONTH OR TWO AGO.
SOUTH OF THE INTERSTATE 70 CORRIDOR, A MORE UNSTABLE AIRMASS
IS PRESENT, CHARACTERIZED BY MID-UPPER 70S DEWPOINTS AND MLCAPE
VALUES NEAR 2000 J/KG. EFFECTIVE BULK SHEAR REMAINS LOW AT 25
KT OR LESS, MAKING ORGANIZED/WIDESPREAD SEVERE WEATHER UNLIKELY.
THE STORM PREDICTION CENTER HAS PLACED THIS SOUTHERN TIER UNDER
A MARGINAL RISK FOR SEVERE THUNDERSTORMS INTO EARLY EVENING.
CONVECTIVE ELEMENTS WITHIN THIS ZONE ARE CAPABLE OF PRODUCING
ISOLATED DAMAGING WIND GUSTS DUE TO PRECIP LOADING AND
TORRENTIAL RAINFALL. HREF HOURLY PROBABILITY FIELDS SHOW A 40%
CHANCE OF LOCALIZED RAINFALL AMOUNTS EXCEEDING 1 INCH, WHICH
RAISES THE POTENTIAL FOR ISOLATED/LOCALIZED FLASH FLOODING
SUNDAY MORNING, A WARM FRONT SWINGS NORTH ACROSS THE CWA,
BRINGING A LOW (20-30%) CHANCE OF AN ISOLATED SHOWER OR STORM.
BEHIND THE FRONT, WINDS VEER SOUTHEAST TO SOUTH THROUGH
AFTERNOON AND UPPER-LEVEL HEIGHTS RISE RAPIDLY AS A SUB-
TROPICAL RIDGE EXPANDS NORTHWARD FROM THE GULF COAST. NBM
GUIDANCE INDICATES HIGH TEMPERATURES CLIMBING INTO THE LOWER 90S
OVER THE SOUTHWEST HALF OF THE CWA. PAIRED WITH HIGH AMBIENT
HUMIDITY, HEAT INDEX VALUES ARE PROJECTED TO EXCEED 100 DEGREES
ACROSS MUCH OF THE FORECAST AREA, WITH VALUES UP TO 105 DEGREES
IN SOUTHEAST AND WEST CENTRAL ILLINOIS. A HEAT ADVISORY GOES
INTO EFFECT SUNDAY AFTERNOON SOUTHWEST OF A PEORIA TO ROBINSON
LINE TO ADDRESS THESE CONDITIONS.
AN INTENSE AND PROLONGED HEAT WAVE WILL DOMINATE THE WEATHER
PATTERN ACROSS CENTRAL AND SOUTHEAST ILLINOIS THROUGH
MIDWEEK. STRONG MULTI-MODEL CONSENSUS AMONG THE GEFS AND ECMWF
ENSEMBLES SHOWS A CORE 594 DAM RIDGE ANCHORING OVER THE
MISSISSIPPI AND OHIO RIVER VALLEYS. THE ECMWF EXTREME FORECAST
INDEX (EFI) HIGHLIGHTS VALUES BETWEEN 0.8 AND 0.9 FOR MAXIMUM
TEMPERATURES MONDAY THROUGH WEDNESDAY, SIGNIFYING THAT THE
MAGNITUDE OF THIS HEAT EVENT IS UNUSUAL IN A CLIMATOLOGICAL
CONTEXT FOR THE END OF JUNE. FURTHERMORE, GIVEN LOW-MID 70S
FORECAST DEWPOINTS, PEAK HEAT INDEX VALUES EXCEEDING 105
DEGREES ARE LIKELY DURING THIS TIMEFRAME. HIGH CONFIDENCE
EXISTS REGARDING THE SEVERITY AND MEDIUM CONFIDENCE IN THE
LONGEVITY OF THIS HEAT EVENT, AND THE HEAT ADVISORY WILL LIKELY
REQUIRE EXTENSION THROUGH AT LEAST WEDNESDAY FOR THE ENTIRE CWA.
A FORECAST CHALLENGE EMERGES LATE WEEK REGARDING THE BREAKDOWN
OF THE RIDGE AND THE RETURN OF PRECIPITATION. NOTABLE
DISAGREEMENTS EXIST AMONG MEDIUM RANGE ENSEMBLE GUIDANCE. THE
GFS PRESENTS A FASTER AND MORE PROGRESSIVE UPPER-LEVEL TROUGH
SHIFTING ACROSS THE NORTHERN PLAINS BY THURSDAY, WHICH ACTS TO
SUPPRESS THE RIDGE AND INTRODUCE THUNDERSTORM CHANCES AHEAD OF A
COLD FRONT. IN CONTRAST, THE ECMWF ENS/ECMWF-AI MAINTAIN A
STRONGER RIDGE OVER THE EASTERN UNITED STATES, HOLDING
PRECIPITATION CHANCES AT BAY UNTIL FRIDAY OR SATURDAY. DUE TO
THESE DISCREPANCIES, CONFIDENCE IS BELOW NORMAL REGARDING THE
EXACT TIMING OF STORM CHANCES LATE NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1157 AM CDT SAT JUN 27 2026
CURRENT BATCH OF IFR CEILING OVER CENTRAL IL IS FORECAST TO
LIFT INTO MVFR CATEGORY EARLY THIS AFTERNOON, THEN ABOVE THE
MVFR THRESHOLD LATE AFTERNOON. HOWEVER, IFR CEILINGS ARE
FORECAST TO REDEVELOP OVERNIGHT NEAR A SLOW MOVING BOUNDARY
ALONG THE I-72 CORRIDOR, THEN EXPAND NORTH OVER ALL CENTRAL IL
TERMINALS. THESE CEILINGS SHOULD IMPROVE BY LATE MORNING AS A
WARM FRONT LIFTS ACROSS THE AREA. A FEW SHRA/TSRA COULD
ACCOMPANY THE FRONT, HOWEVER COVERAGE IS TOO LOW TO INCLUDE IN
TAFS AT THIS POINT. WINDS WILL GENERALLY BE LIGHT EASTERLY
THROUGH TONIGHT, THEN FIRMING FROM THE SOUTHEAST AROUND 10 KT
BY LATE MORNING.
ILX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY FROM 1 PM TO 7 PM CDT SUNDAY FOR ILZ027>029-036-
037-040>042-047>054-061-062-066>068-071>073.
KEY MESSAGES...25
DISCUSSION...25
AVIATION...25
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