019
FXUS63 KILX 131059
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
559 AM CDT THU AUG 13 2026
KEY MESSAGES
- DENSE FOG ADVISORY IN EFFECT UNTIL 9 AM CDT FOR AREAS
GENERALLY NORTH OF A QUINCY TO TERRE HAUTE LINE.
- MIDDAY THUNDERSTORM COMPLEX: A DECAYING CLUSTER OF
THUNDERSTORMS TRACKS NEAR/NORTH OF THE I-74 CORRIDOR AROUND
MIDDAY, BRINGING A THREAT FOR ISOLATED SEVERE THUNDERSTORMS
AND EFFICIENT, HEAVY RAINFALL.
- HEAT CONCERNS SOUTH: SOUTH OF THE IMPENDING THUNDERSTORM
DEBRIS, HOT AND HUMID CONDITIONS YIELD HEAT INDICES NEAR 105F.
A HEAT ADVISORY IS ACTIVE THROUGH EARLY EVENING FOR SOUTHEAST
ILLINOIS, AND WILL NEED TO BE EXPANDED NORTHWARD THIS WEEKEND.
- OVERNIGHT FLOOD WATCH: REPEATED THUNDERSTORMS WILL HEIGHTEN
FLASH FLOODING RISKS. A FLOOD WATCH IS IN EFFECT FOR COUNTIES
ALONG/NORTH OF I-74 THROUGH FRIDAY MORNING.
DISCUSSION
ISSUED AT 441 AM CDT THU AUG 13 2026
MORNING DENSE FOG
A STRONG RADIATIONAL COOLING REGIME EARLY THIS MORNING HAS
FOSTERED PATCHY DENSE FOG DEVELOPMENT ACROSS CENTRAL ILLINOIS.
DESPITE HIGH-LEVEL ANVIL DEBRIS STREAMING OVERHEAD FROM UPSTREAM
CONVECTION, LINGERING NEAR-SURFACE MOISTURE AND WEAK BOUNDARY-
LAYER FLOW (WINDS < 10 KT THROUGH 3 KFT) WILL KEEP FOG GROUNDED
PAST DAYBREAK. SHALLOW WARM AIR ADVECTION (WAA) OVERRUNNING THE
EFFECTIVE SURFACE BOUNDARY CURRENTLY DRAPED JUST SOUTH OF THE
FORECAST AREA WILL ALSO AID IN MAINTAINING LOW STRATUS/FOG WELL
INTO THE MID-MORNING HOURS. A DENSE FOG ADVISORY IS IN EFFECT
THROUGH 9 AM CDT FOR LOCATIONS ROUGHLY NORTH OF A QUINCY TO
TERRE HAUTE LINE.
MIDDAY CONVECTIVE COMPLEX & HEAVY RAIN POTENTIAL
ATTENTION THEN SHIFTS TO THE AFTERNOON AS THE FIRST OF MULTIPLE
CONVECTIVE ROUNDS APPROACHES FROM THE WEST. EARLY MORNING RADAR
TRENDS REVEAL A MCC POSITIONED OVER WESTERN IA. SHORT- TERM
HIGH- RESOLUTION GUIDANCE REMAINS IN SOLID CONSENSUS THAT THIS
COMPLEX WILL TRACK NEAR AND NORTH OF THE I-74 CORRIDOR BY
MIDDAY, RIDING ALONG THE NOSE OF A RECEDING LOW-LEVEL JET (LLJ),
A CONVECTIVELY-AUGMENTED SHORTWAVE TROUGH, AND THE NORTHERN
EDGE OF THE INSTABILITY GRADIENT.
SEVERE POTENTIAL WITH THIS INITIAL WAVE REMAINS CONDITIONAL.
WHILE COLD POOL DYNAMICS AND POTENTIAL REAR INFLOW JET (RIJ)
ORGANIZATION BEAR WATCHING, POOR LAPSE RATES, LINGERING MORNING
FOG/STRATUS, AND A PERSISTENT LOW-LEVEL TEMPERATURE INVERSION
COULD KEEP THIS INCOMING ACTIVITY ELEVATED AND PREDOMINANTLY
SUB-SEVERE.
REGARDLESS OF SEVERE RISK, THIS INITIAL ROUND WILL BE AN
EFFICIENT HEAVY RAINFALL PRODUCER. ATMOSPHERIC SOUNDINGS DISPLAY
CLASSIC TROPICAL-LIKE CHARACTERISTICS: (A) ANOMALOUS PWAT
VALUES (2-2.2 INCHES); (B) LOW- TO MID-LEVEL RH EXCEEDING 80%;
(C) A DEEP WARM CLOUD LAYER (> 4KM); AND (D) A LONG, SKINNY
CAPE PROFILE.
LATEST HREF 6-HOUR PROBABILITY-MATCHED MEAN (PMM) QPF TARGETS
0.5 TO 1.5 INCHES ACROSS THE NORTHERN FORECAST AREA WITH THIS
INITIAL MIDDAY PUSH.
HEAT & HUMIDITY ACROSS THE SOUTH
SOUTH OF THE CONVECTIVE FOOTPRINT AND THE EFFECTIVE SURFACE
BOUNDARY (PRIMARILY SOUTH OF A QUINCY TO TERRE HAUTE LINE),
STRONG SURFACE HEATING AND RICH MOISTURE WILL PERSIST. HIGHS
NEAR 90 PAIRED WITH DEWPOINTS IN THE MID 70S WILL YIELD HEAT
INDEX VALUES BETWEEN 100-105F. A HEAT ADVISORY IS IN EFFECT
THROUGH EARLY EVENING FOR PORTIONS OF SOUTHEAST ILLINOIS.
OVERNIGHT FLASH FLOOD THREAT
THE THREAT FOR FLASH FLOODING ESCALATES SIGNIFICANTLY TONIGHT
ACROSS CENTRAL AND NORTHERN ILLINOIS. THE EFFECTIVE SURFACE
BOUNDARY WILL BEGIN TO RETREAT NORTHWARD AS A SHARPENING WARM
FRONT. AN INTENSIFYING NOCTURNAL LLJ IMPINGING DIRECTLY ONTO
THIS ELEVATED BAROCLINIC ZONE WILL FUEL REPEATED CONVECTIVE
INITIATION AND TRAINING THUNDERSTORM COMPLEXES NEAR AND NORTH OF
THE I-74 CORRIDOR.
WITH ANTECEDENT CONDITIONS POTENTIALLY PRIMED BY THE MIDDAY
CONVECTIVE ROUND, SUSCEPTIBILITY TO RAPID RUNOFF COULD BE HIGH.
HREF QPF PMM GUIDANCE INDICATES AN ADDITIONAL 1-2 INCHES
OVERNIGHT, WITH MESOSCALE TRAINING CORRIDORS CAPABLE OF
PRODUCING LOCALIZED TOTALS EXCEEDING 4 INCHES. GIVEN THE HIGH-
EFFICIENCY AIRMASS AND HIGH POTENTIAL FOR TRAINING, A FLOOD
WATCH HAS BEEN ISSUED FOR COUNTIES ALONG AND NORTH OF I-74
THROUGH FRIDAY MORNING.
THIS WEEKEND THROUGH MID-NEXT WEEK
THE SURFACE WARM FRONT IS PROJECTED TO SURGE NORTH OF THE AREA
FRIDAY NIGHT INTO SATURDAY, RE-INTRODUCING TRIPLE- DIGIT HEAT
INDICES AND SCATTERED ELEVATED WARM-ADVECTION CONVECTION TO
START THE WEEKEND. THE HEAT ADVISORY WILL MOST LIKELY NEED TO BE
EXPANDED NORTHWARD FOR FRIDAY AND SATURDAY.
A STRONGER, MORE POTENT SHORTWAVE TROUGH IS THEN FORECAST TO
DIG OUT OF THE NORTHERN PLAINS SUNDAY INTO MONDAY, DRIVING A
SHARPER SURFACE COLD FRONT THROUGH THE MISSISSIPPI VALLEY. WHILE
SHOWERS AND THUNDERSTORMS MAY ACCOMPANY THE FRONTAL PASSAGE,
DETERMINISTIC MODELS AND GLOBAL ENSEMBLES SHOW REMARKABLY STRONG
CONSENSUS FOR A DEEPER CONTINENTAL POLAR (CP) AIRMASS TO PUSH
INTO THE CENTRAL U.S. EARLY NEXT WEEK. THIS WILL USHER IN A
PERIOD OF BELOW-NORMAL TEMPERATURES, LOWER DEWPOINTS, AND AN
EXTENDED BREAK FROM THE ACTIVE CONVECTIVE PATTERN BY MONDAY AND
TUESDAY.
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 538 AM CDT THU AUG 13 2026
MVFR TO IFR FOG/LOW STRATUS CONTINUES TO EXPAND THIS MORNING
WITH THE WORST CONDITIONS NEAR AND NORTH OF THE I-74 CORRIDOR.
VISIBILITY SHOULD IMPROVE BEYOND 13Z, THOUGH CEILINGS AT
NORTHERN TERMINALS WILL REMAIN MVFR FOR AT LEAST THE FIRST HALF
OF THE DAY.
A DECAYING THUNDERSTORM COMPLEX WILL APPROACH THE CENTRAL
ILLINOIS TERMINALS BY EARLY AFTERNOON, WITH THE HIGHEST
PROBABILITIES OF TSRA AT KPIA AND KBMI. PROB30 GROUPS ARE NOTED
AT THE REMAINING SITES WHERE CONFIDENCE REMAINS LOWER.
ADDITIONAL STORMS ARE POSSIBLE NEAR/NORTH OF I-74 LATE TONIGHT
WITH PROB30 GROUPS MAINTAINED FOR THIS POTENTIAL. EASTERLY
WINDS WILL LARGELY REMAIN IN PLACE THROUGH THE PERIOD, WITH THE
DIRECTION MORE VARIABLE WITH ANY STORM ACTIVITY.
ILX WATCHES/WARNINGS/ADVISORIES
DENSE FOG ADVISORY UNTIL 9 AM CDT THIS MORNING FOR ILZ027>031-
036>038-041>046-053-055-057.
FLOOD WATCH FROM 10 AM CDT THIS MORNING THROUGH FRIDAY MORNING
FOR ILZ027>031-037-038-045-046.
HEAT ADVISORY FROM NOON TODAY TO 8 PM CDT SUNDAY FOR
ILZ066>068-071>073.
KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...MJA
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