975
FXUS63 KILX 312006
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
306 PM CDT FRI JUL 31 2026
KEY MESSAGES
- LOCALIZED FLASH FLOODING IS THE PRIMARY CONCERN THROUGH
SATURDAY MORNING, PARTICULARLY ALONG THE I-74 CORRIDOR DUE TO
REPEATED ROUNDS OF HEAVY RAIN. EXPECT RAINFALL TOTALS OF 1.5
TO 3.0 INCHES IN THESE PERSISTENT BANDS, WITH SIGNIFICANTLY
LOWER AMOUNTS ELSEWHERE.
- A LOW-PROBABILITY, CONDITIONAL THREAT FOR A STRAY DAMAGING
WIND GUST OR BRIEF TORNADO EXISTS TONIGHT, PRIMARILY ACROSS
WEST-CENTRAL AND SOUTHWEST ILLINOIS. WHILE MOST STORM ACTIVITY
WILL REMAIN SUB-SEVERE, REMAIN ALERT FOR UPDATES.
- PLEASANT, DRY, AND WARM WEATHER FOLLOWS FOR MONDAY AND
TUESDAY, BEFORE RAIN CHANCES RETURN MID-TO-LATE NEXT WEEK.
CONFIDENCE IN THE LATE-WEEK TIMING REMAINS LOW, SO PLEASE
CHECK BACK FOR LATER FORECASTS.
DISCUSSION
ISSUED AT 253 PM CDT FRI JUL 31 2026
SHORT TERM
(TONIGHT THROUGH SATURDAY NIGHT)
AFTERNOON WATER VAPOR IMAGERY DEPICTS A ROBUST SHORTWAVE TROUGH
POSITIONED OVER NORTHERN IOWA, WITH A BROAD MID-LEVEL DRY SLOT
BEGINNING TO WRAP INTO THE SYNOPTIC SYSTEM. AS THIS DRY SLOT
PUSHES ACROSS CENTRAL ILLINOIS OVER THE NEXT FEW HOURS, OVERALL
RAINFALL COVERAGE IS FORECAST TO GREATLY DIMINISH INTO THE
EVENING. MODEL GUIDANCE REMAINS IN FIRM AGREEMENT THAT THE
PRIMARY UPPER-LEVEL LOW WILL MEANDER INTO CENTRAL ILLINOIS
OVERNIGHT WHILE BEGINNING ITS OCCLUSION AND FILLING PROCESS.
SHOWER AND THUNDERSTORM COVERAGE WILL RAMP BACK UP TONIGHT AS
THE COLD-CORE LOW DRIFTS INTO THE AREA. STEEPENING MID- LEVEL
LAPSE RATES ASSOCIATED WITH THE COLD POCKET ALOFT WILL YIELD A
SUBTLE BOOST IN CAPE, SUPPORTING INCREASED OVERNIGHT THUNDER
POTENTIAL. WHILE THERE IS A NON-ZERO CHANCE FOR SURFACE- BASED
CONVECTION NEAR THE SYNOPTIC TRIPLE POINT, PRIMARILY ACROSS
WEST- CENTRAL AND SOUTHWEST ILLINOIS, THE OVERWHELMING
EXPECTATION IS FOR MOST ACTIVITY TO REMAIN ELEVATED AND SUB-
SEVERE LATE TONIGHT. NONETHELESS, LOW LCLS, BACKED LOW-LEVEL
WINDS, AND LOCALLY ENHANCED STORM-RELATIVE HELICITY (SRH) NEAR
THE TRIPLE POINT WARRANT KEEPING A CLOSE EYE ON A LOW-
PROBABILITY, CONDITIONAL THREAT FOR A STRAY DAMAGING WIND GUST
OR BRIEF TORNADO. THE PRIMARY LIMITING FACTOR AND SOURCE OF
UNCERTAINTY IS THE MAGNITUDE OF LOW-LEVEL CAPE NECESSARY TO
FOSTER BOUNDARY LAYER STRETCHING; AT PRESENT, THIS REMAINS AN
UNLIKELY SCENARIO.
THE PRIMARY HAZARD OVERNIGHT INTO SATURDAY MORNING WILL SHIFT
TOWARD LOCALIZED FLASH FLOODING RATHER THAN SEVERE WEATHER.
WEAK AMBIENT FLOW BENEATH THE UPPER LOW WILL FOSTER SLUGGISH
CELL MOTION, OPENING THE DOOR FOR TRAINING CONVECTIVE BANDS.
HIGH- RESOLUTION HREF LPMM GUIDANCE CONTINUES TO HIGHLIGHT
LOCALIZED HEAVY RAINFALL CORES OF 1.5 TO 3.0 INCHES WHERE
CONVECTIVE TRAINING ALIGNS ALONG THE OCCLUDED FRONT, MOST
NOTABLY AS THE SYSTEM'S COMMA HEAD DRIFTS SOUTHWARD ALONG THE
I-74 CORRIDOR SATURDAY MORNING. CONVERSELY, AREAS POSITIONED
DIRECTLY BENEATH THE SURFACE LOW TRACK (ROUGHLY FROM SPRINGFIELD
TO TERRE HAUTE) MAY SEE A RELATIVE FOOTPRINT MINIMUM, TOTALING
0.50 TO 0.75 INCHES OR LESS.
AS THE DEFORMATION ZONE AND PRIMARY LOW SLOWLY SLIDE EAST
TOWARD THE WABASH RIVER VALLEY LATE SATURDAY, LOW STRATUS AND
LINGERING LIGHT SHOWERS WILL PERSIST INTO SATURDAY EVENING OR
EARLY SUNDAY MORNING ACROSS EASTERN ILLINOIS BEFORE DRY AIR
ADVECTION TAKES FULL CONTROL BY SUNDAY AFTERNOON.
LONG TERM
(SUNDAY NIGHT THROUGH FRIDAY)
UPPER-LEVEL HEIGHT RISES AND AN AMPLIFYING WESTERN RIDGE WILL
BUILD INTO THE GREAT LAKES REGION EARLY NEXT WEEK, MARKING A
SWIFT TRANSITION BACK TO SEASONABLY WARM, DRY, AND PLEASANT
SUMMER WEATHER FOR MONDAY AND TUESDAY. HIGH TEMPERATURES WILL
COMFORTABLY REBOUND INTO THE MID-80S BENEATH MOSTLY SUNNY SKIES.
THE NEXT OPPORTUNITY FOR ORGANIZED PRECIPITATION ARRIVES MID-
WEEK AS A ROBUST NORTHERN-STREAM SHORTWAVE DRIVES A COLD FRONT
TOWARD THE UPPER MIDWEST. GUIDANCE EXHIBITS CONSIDERABLE SPREAD
REGARDING HOW FAR SOUTH THIS BOUNDARY CAN PENETRATE INTO
CENTRAL ILLINOIS AS ITS PARENT UPPER-LEVEL DYNAMICS RAPIDLY
DISPLACE EASTWARD INTO CANADA. WILL MAINTAIN CONSERVATIVE 20-30%
POPS FOR WEDNESDAY THROUGH THURSDAY TO ACCOUNT FOR THESE TIMING
AND BOUNDARY-POSITION UNCERTAINTIES.
HOWEVER, RECENT DETERMINISTIC AND ENSEMBLE GUIDANCE HINTS AT A
SECONDARY REINFORCING SHORTWAVE DIGGING ACROSS THE PLAINS AND
RIDING ALONG THE QUASISTATIONARY SURFACE BOUNDARY THURSDAY. THIS
WOULD INCREASE LOCAL BAROCLINICITY AND REINVIGORATE THE COLD
FRONT, DRIVING IT SOUTHWARD ACROSS THE LOCAL FORECAST AREA. THIS
LATTER SCENARIO WOULD FAVOR HIGHER PROBABILITIES FOR SHOWERS
AND THUNDERSTORMS DURING THE THURSDAY INTO FRIDAY TIMEFRAME AND
WILL BEAR WATCHING IN FUTURE GUIDANCE UPDATES.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 1240 PM CDT FRI JUL 31 2026
FLIGHT CONDITIONS WILL GRADUALLY DETERIORATE THIS EVENING AS THE
CENTER OF SURFACE LOW PRESSURE TRACKS DIRECTLY OVER THE REGIONAL
TERMINALS. THIS SHOULD RESULT IN WIDESPREAD IFR/LIFR CEILINGS BY
12Z SATURDAY. THE EXCEPTION TO THIS RULE COULD BE AT
KSPI/KDEC/KCMI, WHERE MVFR CEILINGS COULD LINGER A LITTLE LONGER
OVERNIGHT INTO SATURDAY MORNING AS A WEDGE OF DRIER AIR
OVERSPREADS THE INTERSTATE 72 TERMINALS.
THUNDERSTORM COVERAGE IS FORECAST TO INCREASE PRIOR TO 06Z, WITH
CONTINUED CHANCES EXTENDING THROUGH LATE IN THE TAF PERIOD AS
THE CENTER OF LOW PRESSURE PUSHES DIRECTLY OVERHEAD. IN EFFECT,
SEVERAL PROB30 GROUPS MENTIONING TSRA REMAIN APPROPRIATE AT THIS
TIME.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...MJA
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