636
FXUS63 KILX 100928
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
428 AM CDT MON AUG 10 2026
KEY MESSAGES
- HEAT ADVISORY REMAINS UNCHANGED TODAY; HIGH TEMPERATURES WILL
REACH AROUND 90 DEGREES WITH PEAK HEAT INDICES NEAR 100
DEGREES, THOUGH LINGERING ANVIL DEBRIS AND UPPER-LEVEL
WILDFIRE SMOKE INTRODUCE MINOR TEMPERATURE UNCERTAINTY.
- SEVERE WEATHER THREAT LATE THIS AFTERNOON AND EVENING REMAINS
CONDITIONAL ACROSS CENTRAL AND NORTHEAST ILLINOIS. ISOLATED
DAMAGING WINDS, HAIL, AND A LOCALIZED TORNADO RISK MAY EVOLVE
IF OUR CAPPED ENVIRONMENT BREAKS.
- HIGHER-CONFIDENCE, HIGH-END SEVERE POTENTIAL DEVELOPS BY
MIDDAY TUESDAY NEAR THE I-80 AND I-74 CORRIDORS WHERE EXTREME
WIND GUSTS (70+ MPH) ARE PLAUSIBLE.
- ACTIVE "RING-OF-FIRE" PATTERN MAINTAINS PERIODIC SHOWER AND
THUNDERSTORM CHANCES THROUGH LATE WEEK AND THE WEEKEND.
DISCUSSION
ISSUED AT 424 AM CDT MON AUG 10 2026
NEAR TERM /TODAY THROUGH TONIGHT/
EARLY MORNING INFRARED SATELLITE IMAGERY DEPICTS CENTRAL
ILLINOIS POSITIONED IN A RELATIVE CLOUD LULL BETWEEN DECAYING
CONVECTIVE ANVILS. STRONG SYNOPTIC SUBSIDENCE IN THE WAKE OF
LAST NIGHT'S DEPARTING SHORTWAVE, COUPLED WITH A ROBUST CAPPING
BENEATH AN ELEVATED MIXED LAYER (EML), SHOULD KEEP ADDITIONAL
CONVECTIVE ACTIVITY SUPPRESSED ACROSS THE CWA THROUGH MIDDAY.
EXPECT PARTIAL CLEARING DESPITE UPSTREAM ANVIL DEBRIS GRADUALLY
SPREADING OVERHEAD. WHERE INSOLATION IS MAXIMIZED, AMBIENT
TEMPERATURES SHOULD CLIMB INTO THE UPPER 80S TO LOWER 90S.
HOWEVER, AN ELEVATED PLUME OF WILDFIRE SMOKE STREAMING ACROSS
THE MIDWEST INTRODUCES UNCERTAINTY REGARDING PEAK SURFACE
HEATING. GIVEN THESE CLOUD AND SMOKE NUANCES, THE DECISION WAS
MADE TO HOLD OFF ON EXPANDING THE EXISTING HEAT ADVISORY.
CONVECTIVE POTENTIAL LATE TODAY AND TONIGHT REMAINS HIGHLY
CONDITIONAL. CENTRAL ILLINOIS STAYS EMBEDDED WITHIN AN ACTIVE
NORTHWEST FLOW REGIME ALONG THE NORTHEASTERN PERIPHERY OF THE
HEAT RIDGE. SYNOPTIC-SCALE FORCING APPEARS SUBTLE AT BEST,
THOUGH A MINOR MID-LEVEL SHORTWAVE IMPULSE IS MODELED TO DIG
ACROSS NORTHERN ILLINOIS TOWARD NORTHERN INDIANA BY EARLY
EVENING. CONVECTIVE INITIATION MAY FOCUS NEAR THIS FEATURE
ACROSS NORTHEAST ILLINOIS AS A LOW-LEVEL JET (LLJ) STRENGTHENS
AND VEERS ATOP A WEAK SYNOPTIC BOUNDARY. MESOSCALE COMPLEXITY IS
FURTHER ELEVATED BY A PAIR OF LINGERING OUTFLOW BOUNDARIES NEAR
THE I-74 CORRIDOR FROM MONDAY EVENING'S CONVECTION, THOUGH IT
REMAINS UNCERTAIN HOW EFFECTIVELY THESE BOUNDARIES WILL MIX OUT
DURING AFTERNOON HEATING.
GIVEN THE RELIANCE ON SUBTLE MESOSCALE FEATURE INTERACTIONS
RATHER THAN ROBUST SYNOPTIC FORCING, CAM GUIDANCE IS EXPECTED TO
EXHIBIT LOWER-THAN-AVERAGE SKILL TONIGHT. HOWEVER, IF THE
STRONG CAPPING CAN BE OVERCOME, EXTREME BUOYANCY (MUCAPE
EXCEEDING 4000 J/KG) COUPLED WITH MODEST DEEP-LAYER SHEAR (20-30
KT) WILL FAVOR ORGANIZED MULTI-CELLS OR SUPERCELLS CAPABLE OF
PRODUCING DAMAGING WINDS, LARGE HAIL, AND TORRENTIAL RAINFALL.
ADDITIONALLY, THE NOCTURNAL STRENGTHENING OF THE LLJ WILL
ELONGATE LOW-LEVEL HODOGRAPHS, YIELDING A CONDITIONAL TORNADO
THREAT NEAR ANY LINGERING BOUNDARY INTERACTIONS.
SHORT TERM /TUESDAY THROUGH WEDNESDAY/
A MORE ORGANIZED AND HIGH-IMPACT SEVERE THREAT ARRIVES BY
MIDDAY TUESDAY. GUIDANCE REMAINS IN GOOD AGREEMENT ON A COMPACT,
POTENT SHORTWAVE TROUGH EMBEDDED WITHIN AN ENHANCED BELT OF
MID- LEVEL WESTERLIES PUSHING ACROSS THE I-80 CORRIDOR FROM
CENTRAL IOWA INTO NORTHWEST INDIANA. CAMS INDICATE MORNING
CONVECTION WILL LIKELY BE ONGOING ALONG A STALLED SURFACE
BOUNDARY IN ASSOCIATION WITH THIS FEATURE.
TAKING AN INGREDIENTS-BASED APPROACH, THE SYNOPTIC PATTERN
PRESENTS A CLASSIC PROGRESSIVE DERECHO SETUP ACROSS NORTHERN AND
NORTH-CENTRAL ILLINOIS: (A) EXTREME INSTABILITY: MUCAPE POOLING
AROUND 4000 J/KG IN THE VICINITY OF THE QUASI-STATIONARY FRONT;
(B) COLD POOL / RIJ DYNAMICS: SUBSTANTIAL MID-LEVEL DRY AIR
ENTRAINMENT FAVORING STRONG EVAPORATIVE COOLING, ROBUST COLD
POOL PROPAGATION, AND REAR INFLOW JET (RIJ) ACCELERATION; AND
(C) KINEMATICS: STRONG, LARGELY UNIDIRECTIONAL DEEP-LAYER SHEAR
(30-40 KTS) PARALLEL TO THE CONVECTIVE LINE VECTOR,
COMPLEMENTED BY A 30 KT LOW-LEVEL JET TO FEED WARM/MOIST AIR
INTO THE CONVECTIVE SYSTEM.
WHILE THE PRIMARY SWATH OF HIGH-END SEVERE WEATHER IS CURRENTLY
FAVORED ACROSS NORTHERN ILLINOIS, THE SOUTHERN FLANK OF THE
CONVECTIVE SYSTEM, OR ITS COLD POOL OUTFLOW, COULD EASILY SKIM
THE I-74 CORRIDOR. THIS BOUNDARY WOULD PRESENT A SEVERE WIND
THREAT MIDDAY, WHILE SERVING AS A POTENTIAL FOCUS FOR CONVECTIVE
REDEVELOPMENT LATER TUESDAY EVENING. THIS REMAINS THE PRIMARY
FORECAST HAZARD OVER THE NEXT 36 HOURS.
BY WEDNESDAY, THE SURFACE FRONT REMAINS DRAPED OVER THE REGION
BENEATH THE PERSISTENT UPPER RIDGE TO THE WEST. WHILE CAPE AND
SHEAR PARAMETERS DECREASE SLIGHTLY RELATIVE TO TUESDAY'S
ANOMALOUS VALUES, SUFFICIENT INSTABILITY AND SHEAR OVERLAP WILL
SUSTAIN A MARGINAL RISK FOR SEVERE WEATHER AS SUBTLE RIDGE-
RIDING IMPULSES TRACK THROUGH THE FLOW.
LONG TERM /THURSDAY THROUGH SUNDAY/
A MORE DEFINED LONGWAVE TROUGH IS PROJECTED TO DIG INTO THE
UPPER GREAT LAKES BY THURSDAY, PROVIDING THE NECESSARY PUSH TO
DRIVE THE SURFACE FRONT SOUTHWARD INTO CENTRAL ILLINOIS. THE
BOUNDARY WILL LIKELY WAVER ACROSS THE CENTRAL PORTION OF THE
STATE THROUGH SATURDAY BEFORE LIFTING NORTHWARD AS A WARM FRONT
OVER THE WEEKEND. DEEP MOISTURE AND INSTABILITY LAID OUT ALONG
THIS BOUNDARY, COMBINED WITH ADDITIONAL RIDGE-RIDERS, WILL
MAINTAIN DAILY CHANCES FOR SHOWERS AND THUNDERSTORMS THROUGH
SUNDAY. THE EXCEPTION MAY BE SATURDAY, WHEN THE UPPER RIDGE AXIS
BRIEFLY BUILDS OVERHEAD TO PROVIDE A BRIEF LULL IN CONVECTIVE
ACTIVITY.
AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 1203 AM CDT MON AUG 10 2026
A CLUSTER OF THUNDERSTORMS IS ONGOING NORTH OF I-74 IN NORTHERN
ILLINOIS LATE TONIGHT. THE LATEST SUITE OF GUIDANCE SUGGESTS THE
MAJORITY OF THIS ACTIVITY WILL REMAIN NORTH OF THE TERMINALS WITH A
LOW CHANCE (30%) THAT STORMS GRAZE KBMI AND KCMI THROUGH EARLY
MONDAY MORNING. BEYOND THAT, SHOWER AND STORM CHANCES LOOK TO BE
RELATIVELY LOW THROUGH MONDAY, BUT CONFIDENCE DECREASES BY MONDAY
NIGHT. SOUTH WINDS WILL VEER TO THE SOUTHWEST BY LATE MORNING WITH
GUSTS OCCASIONALLY TOUCHING 20 KTS. WINDS WILL EASE BY MONDAY
NIGHT AND RETREAT TO THE SOUTH.
ILX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY FROM NOON TODAY TO 7 PM CDT THIS EVENING FOR
ILZ040-047>052-061>063-066>068-071>073.
KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...NMA
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