535
FXUS63 KILX 091813
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
113 PM CDT SUN AUG 9 2026
KEY MESSAGES
- DANGEROUS HEAT CONTINUES THROUGH WEDNESDAY, WITH PEAK HEAT
INDEX VALUES BETWEEN 100 AND 109 DEGREES DAILY. A HEAT
ADVISORY REMAINS IN EFFECT THROUGH MONDAY ALONG AND SOUTH OF A
CANTON TO CASEY LINE. ADDITIONAL HEADLINES MAY EVENTUALLY BE
NEEDED TUESDAY AND WEDNESDAY.
- SEVERE THUNDERSTORMS AND HEAVY RAINFALL ARE POSSIBLE
OVERNIGHT AND AGAIN MONDAY NIGHT INTO TUESDAY. THE GREATEST
RISKS WITH THESE STORMS WILL BE DAMAGING WINDS AND LOCALIZED
FLOODING.
DISCUSSION
ISSUED AT 107 PM CDT SUN AUG 9 2026
SYNOPTIC OVERVIEW...
THE SYNOPTIC PATTERN REMAINS DOMINATED BY A ROBUST 595 DAM
UPPER-LEVEL RIDGE CENTERED OVER THE FOUR CORNERS, MAINTAINING
PERSISTENT NORTHWESTERLY FLOW ACROSS THE GREAT LAKES. CENTRAL
ILLINOIS RESIDES ON THE PERIPHERY OF THIS FEATURE, EFFECTIVELY
PLACING THE REGION WITHIN THE RING OF FIRE NEAR A QUASI-
STATIONARY BAROCLINIC ZONE. THIS CONFIGURATION ENSURES HOT,
HUMID CONDITIONS AND A CHALLENGING CONVECTIVE FORECAST, AS
MODELS CONTINUE TO STRUGGLE WITH THE PRECISE TIMING AND
EVOLUTION OF SUCCESSIVE NOCTURNAL MESOSCALE CONVECTIVE SYSTEMS
(MCS).
SHORT-TERM CONVECTIVE POTENTIAL...
REGIONAL RADAR IMAGERY HIGHLIGHTS AN MCV FROM EARLIER UPSTREAM
CONVECTION TRAVERSING SOUTHERN WISCONSIN, WHICH IS DRIVING
CONVECTIVE REDEVELOPMENT OVER THE CHICAGO METRO AREA. LOCALLY,
CAPPING (MLCIN > 100 J/KG) CONTINUES TO SUPPRESS ACTIVITY,
THOUGH AN OUTFLOW BOUNDARY CURRENTLY MOVING ACROSS THE
MISSISSIPPI RIVER NORTH OF QUINCY REMAINS A FOCAL POINT FOR
POTENTIAL CAP EROSION THIS AFTERNOON. IF DEEP CONVECTION MANAGES
TO INITIATE, EFFECTIVE SHEAR PROFILES OF 25-30 KT (PER THE
LATEST RAP) ARE MARGINALLY SUFFICIENT FOR STORM ORGANIZATION.
CONSEQUENTLY, THUNDERSTORM PROBABILITIES REMAIN LOW (AROUND 20%)
NORTH OF I-72 THROUGH THE EARLY EVENING, BUT IF STORMS DO
DEVELOP THEY COULD BE STRONG.
OVERNIGHT, THE LOW-LEVEL JET (LLJ) IS FORECAST TO INTENSIFY,
FOCUSING MOISTURE CONVERGENCE ALONG THE INSTABILITY GRADIENT TO
OUR NORTH. WHILE THE CONSENSUS OF CAMS TRACKS THE PRIMARY MCS
ACTIVITY ACROSS NORTHERN ILLINOIS INTO INDIANA, THE ORIENTATION
OF CORFIDI VECTORS FROM THE NORTHEAST WARRANTS CAUTION. SHOULD
UPSTREAM DEVELOPMENT ALIGN FAVORABLY, THERE REMAINS POTENTIAL
FOR PROPAGATION INTO CENTRAL ILLINOIS. PRIMARY CONCERNS WITH ANY
NOCTURNAL DEVELOPMENT WOULD BE LOCALLY HEAVY RAIN DUE TO
BACKBUILDING AND A DAMAGING WIND THREAT; TRENDS WILL BE
MONITORED CLOSELY THROUGH THE OVERNIGHT HOURS.
HEAT AND INSTABILITY: MONDAY - WEDNESDAY...
A PERSISTENT 850MB THERMAL RIDGE WILL DOMINATE THE GREAT PLAINS
AND UPPER MIDWEST REGIONS THROUGH MID-WEEK, PUSHING
TEMPERATURES INTO THE 90S ACROSS WESTERN AND SOUTHERN COUNTIES
OF CENTRAL ILLINOIS. SUSTAINED DEW POINTS IN THE MID-70S WILL
RESULT IN PEAK HEAT INDICES RANGING FROM 100 TO 109 DEGREES
DAILY. A HEAT ADVISORY REMAINS IN EFFECT FOR AREAS SOUTH OF A
CANTON TO CASEY LINE FOR MONDAY. WHILE ADDITIONAL HEADLINES MAY
BE REQUIRED TUESDAY AND WEDNESDAY, UNCERTAINTY REGARDING THE
EXTENT OF CONVECTIVE DEBRIS AND OUTFLOW BOUNDARIES CURRENTLY
PRECLUDES ADDITIONAL PRODUCT ISSUANCE.
THE CONVECTIVE PATTERN REMAINS HIGHLY REPETITIVE FOR THE FIRST
HALF OF THE WEEK. MONDAY EVENING FEATURES AN ENVIRONMENT WITH
VERY STRONG INSTABILITY, WITH GFS-PROGGED MLCAPE VALUES
APPROACHING 4000 J/KG, SUPPORTED BY 25-35 KT OF DEEP-LAYER
SHEAR. WHILE THE PRIMARY AXIS OF MOISTURE CONVERGENCE WILL SHIFT
SLIGHTLY SOUTH, CORFIDI VECTORS AGAIN FAVOR A SOUTHWARD
PROPAGATION PATH INTO CENTRAL ILLINOIS. SIMILAR CONDITIONS WILL
BE IN PLACE TUESDAY AND TUESDAY NIGHT. DESPITE THE PERSISTENT
POPS, IT IS IMPORTANT TO EMPHASIZE THAT NUMEROUS DRY HOURS WILL
PERSIST BETWEEN CONVECTIVE WAVES.
EXTENDED OUTLOOK: THURSDAY - WEEKEND...
BY THE LATTER HALF OF THE WEEK, WESTERN CONUS RIDGING WILL
AMPLIFY, FOSTERING DEEPER DOWNSTREAM TROUGHING OVER THE GREAT
LAKES. THIS SHIFT WILL PLACE CENTRAL ILLINOIS ON THE COOLER SIDE
OF THE BAROCLINIC ZONE, LEADING TO A TRANSITION TOWARD NEAR- TO
SLIGHTLY-BELOW-NORMAL TEMPERATURES. WHILE THE AIRMASS WILL
MODERATE, THE LLJ WILL CONTINUE TO PROVIDE SUFFICIENT FORCING TO
MAINTAIN DAILY CHANCES FOR SHOWERS AND THUNDERSTORMS,
PARTICULARLY DURING THE EVENING AND OVERNIGHT PERIODS.
AVIATION /18Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 1258 PM CDT SUN AUG 9 2026
1745Z/1245PM RADAR IMAGERY SHOWS A LINE OF THUNDERSTORMS
TRACKING EASTWARD ACROSS NORTHERN ILLINOIS TOWARD LAKE MICHIGAN.
MEANWHILE FURTHER SOUTHWEST ALONG/AHEAD OF THE TRAILING OUTFLOW
BOUNDARY, A BROKEN LINE OF LIGHT SHOWERS CONTINUES TO DROP
SOUTHEASTWARD THROUGH THE ILLINOIS RIVER VALLEY. BASED ON
MESOANALYSIS SHOWING CAPPING AND A CONSISTENT SIGNAL FROM MOST
CAMS, HAVE ONLY CARRIED VCSH AT KPIA/KBMI/KSPI THROUGH 20Z/21Z.
ONCE THIS LINE PASSES, THE ACCOMPANYING MID-LEVEL OVERCAST WILL
SCATTER...LEAVING BEHIND MOSTLY CLEAR CONDITIONS EARLY THIS
EVENING. THE NEXT AVIATION FORECAST CHALLENGE WILL REVOLVE
AROUND CONVECTIVE RE-DEVELOPMENT TONIGHT AS THE NOCTURNAL LOW-
LEVEL JET STRENGTHENS. BASED ON MODEL CONSENSUS, IT APPEARS
SCATTERED CELLS WILL FORM ALONG/NORTH OF I-74 BY MID-EVENING,
THEN TRACK E/SE INTO INDIANA TOWARD DAWN MONDAY. AS SUCH, HAVE
INCLUDED PROB30 GROUPS FOR THUNDER AT KPIA/KBMI/KCMI BEGINNING
AT 02Z IN KPIA AND ENDING AT 10Z IN KCMI. AFTER THIS ACTIVITY
DEPARTS, DRY CONDITIONS ARE ANTICIPATED ACROSS THE BOARD THROUGH
18Z MON.
ILX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR ILZ027-036-040-
041-047>051.
HEAT ADVISORY FROM NOON TO 7 PM CDT MONDAY FOR ILZ036-040-041-
047>052-061>063-066>068-071>073.
KEY MESSAGES...DEUBELBEISS
DISCUSSION...DEUBELBEISS
AVIATION...BARNES
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