228
FXUS63 KILX 260029
AFDILX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE LINCOLN IL
729 PM CDT FRI JUL 25 2025
KEY MESSAGES
- A LOW PROBABILITY (5-15% CHANCE) OF SEVERE WEATHER EXISTS NORTH
OF THE I-70 CORRIDOR BOTH TODAY AND SATURDAY.
- A HEAT ADVISORY IS IN EFFECT ALONG AND SOUTH OF A QUINCY TO
PARIS LINE THROUGH SATURDAY. THE OPPRESSIVE HEAT WILL SPREAD
BACK NORTHWARD ACROSS ALL OF CENTRAL ILLINOIS SUNDAY THROUGH
TUESDAY AS HEAT INDEX VALUES ONCE AGAIN REACH 105-115.
- MUCH COOLER WEATHER IS ON TAP FOR THE MIDDLE AND END OF NEXT
WEEK...WITH A HIGH PROBABILITY (50-70% CHANCE) THAT HIGHS DROP
BELOW 80 DEGREES BY NEXT THURSDAY.
DISCUSSION
ISSUED AT 217 PM CDT FRI JUL 25 2025
A SLOW-MOVING FRONTAL BOUNDARY STRETCHES FROM TOPEKA, KANSAS, TO
CHICAGO, ILLINOIS. SOUTH OF I-70, A REMNANT OUTFLOW FROM THIS
MORNINGS CONVECTION IS VISIBLE ON SATELLITE AND RADAR. BOTH
BOUNDARIES WILL BE THE FOCUS FOR SCATTERED THUNDERSTORMS THIS
AFTERNOON.
A SEASONABLY HOT AND HUMID AIRMASS IS PRESENT, WITH TEMPERATURES
IN THE MID-TO-UPPER 80S AND DEWPOINTS IN THE MID-70S. THE RAP
ANALYZES MODERATELY BUOYANT BOUNDARY LAYER CONDITIONS (1500-2500
J/KG MLCAPE) ACROSS CENTRAL AND SOUTHEAST IL. MODEST DEEP-LAYER
SHEAR (< 25 KTS) WILL LIMIT SEVERE WEATHER COVERAGE. HOWEVER,
STEEP LOW-LEVEL LAPSE RATES (> 8 C/KM) AMID MODERATE BUOYANCY
COULD SUPPORT MULTI-CELL CLUSTERS CAPABLE OF DAMAGING DOWNBURST
WINDS THROUGH EARLY EVENING.
TONIGHT, BETTER COVERAGE OF SHOWERS AND THUNDERSTORMS WILL EVOLVE
FURTHER NORTH NEAR THE FRONTAL BOUNDARY AS A MODEST (20-25 KT)
LOW-LEVEL JET IMPINGES FROM THE SOUTH. HIGH-RESOLUTION GUIDANCE
HIGHLIGHTS A CORRIDOR OF CONVECTION DEVELOPING NEAR THE FRONTAL
BOUNDARY FROM KANSAS CITY TO CHICAGO. HIGH MOISTURE CONTENT (PW >
2") AND SLOW STORM MOTIONS BRING A POSSIBILITY OF LOCALIZED FLASH
FLOODING. THE 12Z HREF QPF 6-HR PMM SHOWS POCKETS OF 1.5"-2"
OVERNIGHT, MAINLY NORTH OF THE IL RIVER VALLEY, WHERE THE 6-HR
FLASH FLOOD GUIDANCE MAY BE EXCEEDED. A FLOOD WATCH HAS BEEN
ISSUED FOR KNOX, STARK, AND MARSHALL COUNTIES DUE TO THE HIGH
PROBABILITY OF HEAVY RAINFALL.
ADDITIONAL THUNDERSTORM ACTIVITY IS ANTICIPATED LATE SATURDAY
MORNING AND THROUGH THE AFTERNOON AS A CONVECTIVELY-INDUCED
SHORTWAVE/MCV MOVES ACROSS CENTRAL AND NORTHERN IL. ROBUST PWATS
AND A LINGERING LOW-LEVEL JET WILL AGAIN FAVOR LOCALIZED POCKETS
OF +1"/HR RAINFALL RATES. A LOW SEVERE-WEATHER RISK ALSO EXISTS
SOUTH OF THE FRONTAL BOUNDARY AND NEAR ANY RESIDUAL OUTFLOWS.
THE CONTINUED HOT AND HUMID CONDITIONS HAVE PROMPTED AN EXTENSION
AND EXPANSION OF THE HEAT ADVISORY THROUGH SATURDAY AFTERNOON.
HEAT INDEX VALUES OF 100-105 F WILL BE COMMON NEAR AND ESPECIALLY
SOUTH OF THE I-72/DANVILLE CORRIDOR. THIS ADVISORY WILL LIKELY BE
EXTENDED INTO SUNDAY, WITH A POSSIBLE EXTREME HEAT WATCH FOR
MONDAY AND TUESDAY ACROSS PARTS OF CENTRAL AND SOUTHEAST IL. BY
THEN, THE FRONTAL BOUNDARY WILL HAVE SHIFTED NORTH, MITIGATING
RAIN/CONVECTIVE POTENTIAL AND ASSOCIATED TEMPERATURE BUSTS. DAILY
HEAT INDEX VALUES MONDAY AND TUESDAY ARE FORECAST TO SPIKE NEAR
110 F.
A MAJOR PATTERN CHANGE WILL OCCUR BY THE MIDDLE OF NEXT WEEK AS
THE HEAT DOME BREAKS DOWN AND AN EXPANSIVE AREA OF CANADIAN HIGH
PRESSURE SINKS INTO THE UPPER MIDWEST AND GREAT LAKES. DAILY HIGHS
THURSDAY AND FRIDAY MAY NOT EXCEED 80 DEGREES.
MJA
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 727 PM CDT FRI JUL 25 2025
A WEAK FRONTAL BOUNDARY REMAINS STALLED ACROSS CENTRAL ILLINOIS
WITH SCATTERED EVENING THUNDERSTORMS POSSIBLE ACROSS PORTIONS OF
CENTRAL ILLINOIS THROUGH MUCH OF THE PERIOD. CONFIDENCE IN TIMING
DETAILS REMAINS LOW BUT TRYING TO HONE IN ON A COUPLE POSSIBLE
WINDOWS ADVERTISED BY THE LATEST RUNS OF THE HRRR: THE FIRST NEAR
THE ILLINOIS RIVER VALLEY OVERNIGHT; AND THE SECOND WITH AN
APPROACHING LINE OF STORMS LATE SATURDAY AFTERNOON/EARLY EVENING.
OUTSIDE OF THE INFLUENCE OF STORMS, ANTICIPATE VFR CONDITIONS TO
PREVAIL, THOUGH A BRIEF WINDOW OF MVFR CEILINGS CANNOT BE RULED
OUT SATURDAY LATE MORNING AS DIURNAL CU STARTS TO DEVELOP BEFORE
LIFTING BACK TO VFR.
DEUBELBEISS
ILX WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH THROUGH SATURDAY EVENING FOR ILZ027-028-030.
HEAT ADVISORY UNTIL 7 PM CDT SATURDAY FOR ILZ049>057-061>063-
066>068-071>073.
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