318
FXUS63 KILX 070812
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
312 AM CDT FRI AUG 7 2026
KEY MESSAGES
- WE HAVE HIGH CONFIDENCE THAT HOT AND HUMID CONDITIONS WILL
BUILD THIS WEEKEND. PEAK HEAT INDICES WILL APPROACH 100-105 F
ACROSS MUCH OF CENTRAL ILLINOIS ON SUNDAY AND MONDAY.
- THUNDERSTORMS WILL REMAIN ISOLATED AND DISORGANIZED THROUGH
MONDAY, PRIMARILY POSING A THREAT FOR LOCALIZED HEAVY RAIN.
THE RISK FOR ORGANIZED SEVERE THUNDERSTORMS, INCLUDING
DAMAGING WINDS AND LARGE HAIL, INCREASES TUESDAY AND
WEDNESDAY.
- A COLD FRONT WILL SWEEP THROUGH THE REGION LATE NEXT WEEK,
PROVIDING RELIEF FROM THE HEAT. WE HAVE HIGH CONFIDENCE IN THE
ARRIVAL OF COOLER AND DRIER AIR, THOUGH THE EXACT TEMPERATURE
DROP REMAINS UNCERTAIN.
DISCUSSION
ISSUED AT 305 AM CDT FRI AUG 7 2026
DENSE FOG
EARLY MORNING SURFACE ANALYSIS DEPICTS A DIFFUSE, LINGERING
FRONTAL BOUNDARY DRAPED ACROSS CENTRAL ILLINOIS. VERY SUBTLE
LOW-LEVEL SOUTHERLY FLOW IS CURRENTLY OVERRUNNING THIS BOUNDARY,
PROVIDING JUST ENOUGH WEAK LIFT TO POOL MOISTURE BENEATH A
SHALLOW NOCTURNAL INVERSION. AS A RESULT, PATCHY TO LOCALLY
DENSE FOG HAS MATERIALIZED OVER THE PAST FEW HOURS, WITH THE
GREATEST CONCENTRATION OF LOW VISIBILITY CONFINED TO EAST-
CENTRAL ILLINOIS, PRIMARILY EAST OF THE INTERSTATE 55 CORRIDOR.
RECENT GOES-EAST NIGHTTIME MICROPHYSICS RGB IMAGERY AND
AUTOMATED SURFACE OBSERVATIONS CORROBORATE THESE TRENDS, WITH
LOCALIZED VISIBILITIES OCCASIONALLY BOTTOMING OUT AT ONE-QUARTER
OF A MILE OR LESS WITHIN THE MOST PERSISTENT FOG BANKS.
AS WE PROGRESS PAST SUNRISE, THE ONSET OF NORMAL DIURNAL
HEATING WILL EFFECTIVELY MIX THE BOUNDARY LAYER AND QUICKLY
ERODE THE SHALLOW INVERSION. CONCURRENTLY, INCREASING LOW-LEVEL
WARM AIR ADVECTION WILL AID IN SCOURING OUT THE STAGNANT SURFACE
MOISTURE. THIS SHOULD MAKE QUICK WORK OF THE FOG, WITH RAPID
DISSIPATION AND WIDESPREAD IMPROVEMENT EXPECTED BY MID-MORNING.
SYNOPSIS & OVERVIEW
A CLASSIC, ACTIVE SUMMERTIME PATTERN WILL REMAIN ENTRENCHED
ACROSS THE UPPER MIDWEST AND CENTRAL ILLINOIS THROUGH THE MIDDLE
OF NEXT WEEK. THE BROADER SYNOPTIC SETUP IS ANCHORED BY A
SPRAWLING HEAT RIDGE OVER THE CENTRAL PLAINS, KEEPING THE GREAT
LAKES AND CORN BELT POSITIONED ON ITS NORTHEASTERN FLANK WITHIN
PERSISTENT NORTHWEST FLOW ALOFT. MULTIPLE SHORTWAVE IMPULSES
EMBEDDED WITHIN THIS FLOW WILL DIVE SOUTHEASTWARD ACROSS THE
REGION OVER THE COMING DAYS. WHILE THIS NEBULOUS MID-LEVEL
FORCING WARRANTS STEADY DILIGENCE, THE PATTERN LACKS LARGE-SCALE
ORGANIZATION THROUGH EARLY NEXT WEEK, RESULTING IN INTERMITTENT
SHOWER AND THUNDERSTORM CHANCES WITH LOW MESOSCALE
PREDICTABILITY REGARDING EXACT TIMING AND SPATIAL PLACEMENT.
THROUGH MONDAY: BUILDING HEAT & LOW-SHEAR CONVECTION
THERMODYNAMIC PROFILES THROUGH EARLY NEXT WEEK REMAIN
SEASONABLY MOIST AND UNSTABLE, THOUGH LARGELY UNEXTRAORDINARY
FOR MID- AUGUST. HIGH TEMPERATURES MOSTLY IN THE 85 TO 90 DEGREE
RANGE COMBINED WITH SURFACE DEW POINTS POOLING IN THE LOW TO
MID-70S WILL YIELD PEAK AFTERNOON HEAT INDICES BETWEEN 90 AND
100 DEGREES. PEAK HEAT AND HUMIDITY ARE SLATED FOR THE SUNDAY
AND MONDAY TIMEFRAME AS WARM AIR ADVECTION INTENSIFIES AHEAD OF
A DEVELOPING TROUGH TO THE NORTH. HEAT INDICES DURING THIS PEAK
WINDOW WILL APPROACH 100 TO 105 DEGREES ACROSS MUCH OF THE
FORECAST AREA, OVERLAPPING WITH MODERATE TO EXTREME BUOYANCY
(MLCAPE EXCEEDING 2500-3500 J/KG).
DESPITE THIS SUBSTANTIAL CONVECTIVE INSTABILITY, THE THREAT FOR
ORGANIZED SEVERE WEATHER THROUGH MONDAY REMAINS MUTED. MID-
LEVEL FLOW REMAINS WEAK, KEEPING DEEP-LAYER SHEAR LIMITED (0-6
KM SHEAR GENERALLY < 25 KT). CONSEQUENTLY, CONVECTION WILL RELY
PRIMARILY ON LOW-LEVEL JET CONVERGENCE OR MATURED COLD POOL
DYNAMICS, FAVORING PULSE OR MULTI-CELL MODES CAPABLE OF
LOCALIZED HEAVY RAINFALL AND SPORADIC DAMAGING WIND GUSTS.
TUESDAY THROUGH WEDNESDAY: INCREASING SEVERE POTENTIAL
THE POTENTIAL FOR MORE ORGANIZED CONVECTION INCREASES DURING
THE TUESDAY TO WEDNESDAY TIMEFRAME. MODEL GUIDANCE IS IN GOOD
AGREEMENT THAT A STRONGER BELT OF UPPER-LEVEL WESTERLIES AND AN
ACCOMPANYING MID-LEVEL JET STREAK WILL DIP INTO CENTRAL ILLINOIS
AS A DEEPER TROUGH BEGINS TO DIG INTO THE GREAT LAKES. THIS
INCREASE IN KINEMATIC SUPPORT WILL BOOST 0-6 KM BULK SHEAR INTO
THE 30-40+ KNOT RANGE. WHEN OVERLAID UPON THE LINGERING RICH
BOUNDARY LAYER MOISTURE AND STEEP INSTABILITY, THIS KINEMATIC
BOOST WILL RAISE THE CEILING FOR ORGANIZED CONVECTIVE CLUSTERS
(MCSS) AND SEVERE WEATHER RISKS, INCLUDING DAMAGING WINDS AND
HAIL. MESOSCALE DETAILS AND CONVECTIVE TIMING WILL BE REFINED AS
HIGH-RESOLUTION GUIDANCE COMES INTO RANGE.
LATE NEXT WEEK: TROUGHING & PATTERN CHANGE
BY LATE NEXT WEEK, A BROADER PATTERN TRANSITION APPEARS LIKELY
TO TAKE SHAPE. ENSEMBLES SHOW AN AMPLIFYING UPPER TROUGH
CONSOLIDATING OVER THE GREAT LAKES, PUSHING A SURFACE COLD FRONT
SOUTH THROUGH ILLINOIS AND ALLOWING A CONTINENTAL POLAR (CP)
AIR MASS TO GRADUALLY BUILD INTO THE MIDWEST. THIS TRANSITION
WILL USHER IN A COOLER, DRIER, AND MORE STABLE AIR MASS.
HOWEVER, ENSEMBLE CLUSTER ANALYSIS (GEFS/EPS) CONTINUES TO
EXHIBIT NOTABLE SPREAD REGARDING THE TROUGH'S ULTIMATE
AMPLITUDE AND SOUTHWARD EXTENT, LEAVING SOME UNCERTAINTY
REGARDING THE EXACT MAGNITUDE OF THE LATE-WEEK COOLING AND DEW
POINT SUPPRESSION.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 1235 AM CDT FRI AUG 7 2026
ISOLATED SHOWERS HAVE DEVELOPED OVER SOUTHERN ILLINOIS LATE TONIGHT
AND WITH CHANCES LIFTING NORTH TO ABOUT THE I-72 CORRIDOR THROUGH
FRIDAY MORNING. MVFR CEILINGS LOOK INCREASINGLY LIKELY OVERNIGHT FOR
MOST AIRFIELDS, WITH THE HIGHEST PROBABILITIES (80%) BETWEEN THE I-
74 AND I-74 CORRIDORS. OCCASIONAL DROPS TO IFR ARE ALSO POSSIBLE,
WITH CONDITIONS IMPROVING BY LATE MORNING OR EARLY AFTERNOON. LIGHT
SOUTH WINDS CONTINUE OVERNIGHT, VEERING TO THE SOUTHWEST ON
FRIDAY.
ILX WATCHES/WARNINGS/ADVISORIES
DENSE FOG ADVISORY UNTIL 8 AM CDT THIS MORNING FOR ILZ038-
043>046-052>057-061>063.
KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...NMA
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