195
FXUS63 KILX 042324
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
624 PM CDT TUE AUG 4 2026
KEY MESSAGES
- WIDESPREAD SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS CENTRAL
ILLINOIS LATE WEDNESDAY AFTERNOON AND EVENING. WHILE
CONFIDENCE IN RAIN OCCURRING IS HIGH, THE SEVERE WEATHER
THREAT REMAINS UNCERTAIN.
- OFF-AND-ON SHOWERS AND THUNDERSTORMS WILL LINGER THURSDAY AND
FRIDAY AS A COLD FRONT STALLS OVER THE REGION, THOUGH
ORGANIZED SEVERE WEATHER IS NOT EXPECTED.
- HOT AND HUMID CONDITIONS RETURN SUNDAY INTO EARLY NEXT WEEK,
PUSHING HEAT INDEX VALUES NEAR 100 DEGREES. HOWEVER, PASSING
THUNDERSTORM CLUSTERS MAY PERIODICALLY DISRUPT THE INTENSE
HEAT AND LOWER TEMPERATURES.
DISCUSSION
ISSUED AT 259 PM CDT TUE AUG 4 2026
OVERVIEW & SYNOPTIC SETUP
AFTERNOON WATER VAPOR IMAGERY HIGHLIGHTS A COMPLEX AND ACTIVE
UPPER-LEVEL PATTERN FEATURING A TRIO OF KEY SYNOPTIC PLAYERS.
THE FIRST IS A ROBUST SHORTWAVE TROUGH THAT HAS PIVOTED
NORTHEASTWARD INTO ONTARIO. THIS FEATURE IS ACTIVELY DRIVING A
TRAILING COLD FRONT SOUTH INTO THE MIDWEST, WITH THE BOUNDARY
CURRENTLY ANALYZED FROM NEAR MARQUETTE, MI, SOUTHWESTWARD
THROUGH DES MOINES, IA, AND INTO DODGE CITY, KS. AS THE PARENT
UPPER TROUGH CONTINUES TO PULL AWAY, THIS FRONT'S SOUTHWARD
MOMENTUM WILL SLOW TONIGHT. THE FRONT'S PROGRESSION IS ALSO
BEING SUBTLY IMPEDED BY OUR SECOND FEATURE OF INTEREST: A
RETROGRADING CUT-OFF LOW MEANDERING OVER THE TENNESSEE VALLEY.
HOWEVER, THE MAIN DRIVER OF OUR SENSIBLE WEATHER OVER THE NEXT
24-36 HOURS IS THE THIRD FEATURE--A SERIES OF ENERGETIC PACIFIC
NORTHWEST SHORTWAVES. MODEL GUIDANCE REMAINS IN EXCELLENT
AGREEMENT THAT THIS ENERGY WILL CONSOLIDATE AND DIG AGGRESSIVELY
ACROSS THE CORN BELT ON WEDNESDAY. THIS INCOMING FORCING WILL
INTERCEPT AND REINVIGORATE THE SLUGGISH SURFACE COLD FRONT,
ULTIMATELY ACCELERATING IT THROUGH CENTRAL ILLINOIS BY WEDNESDAY
NIGHT.
NEAR TERM /TONIGHT THROUGH WEDNESDAY MORNING/
CONVECTIVE ALLOWING MODELS (CAMS) CONTINUE TO SHOW AN EXCELLENT
CONSENSUS REGARDING A CLUSTER OF NOCTURNAL CONVECTION
DEVELOPING ACROSS IOWA TONIGHT. SUPPORTED BY A SUBTLE, VEERING
25-KT LOW-LEVEL JET (LLJ) OPERATING JUST AHEAD OF THE ADVANCING
COLD FRONT, THIS ACTIVITY IS EXPECTED TO GRADUALLY BLEED
EASTWARD INTO THE ILLINOIS RIVER VALLEY BY EARLY WEDNESDAY
MORNING. AS WE HEAD TOWARD MID-TO-LATE MORNING, THE LLJ WILL
RECEDE, AND A DISTINCT WANING TREND IN CONVECTIVE COVERAGE AND
INTENSITY IS ANTICIPATED AS IT CROSSES THE ILLINOIS RIVER. AND,
WITH ONLY MEAGER INSTABILITY--FORECAST SOUNDINGS SHOW ONLY A
FEW HUNDRED J/KG OF MUCAPE COLLOCATED WITH THE LLJ AXIS-- EVEN A
THUNDER MENTION EARLY WEDNESDAY MORNING MAY BE A STRETCH.
SHORT TERM /WEDNESDAY AFTERNOON THROUGH FRIDAY/
THE MOST IMPACTFUL WEATHER OF THE WEEK ARRIVES WEDNESDAY
AFTERNOON AND EVENING. AS THE AFOREMENTIONED STRONGER SHORTWAVE
ENERGY BEGINS TO EJECT ACROSS THE FRONT, DEEP-LAYER ASCENT AND
WIND SHEAR WILL INCREASE MARKEDLY.
THIS SETS THE STAGE FOR A MARGINALLY SEVERE, YET HIGHLY
CONDITIONAL, CONVECTIVE THREAT. FROM A PARAMETER SPACE
PERSPECTIVE, THE LATEST HREF PAINTS A FAVORABLE ENVIRONMENT
FEATURING ROUGHLY 1500 J/KG OF SBCAPE JUXTAPOSED WITH 30 KTS OF
0-6 KM BULK SHEAR. HOWEVER, THE CAVEAT--AND IT IS A SIGNIFICANT
ONE--IS THE PRESENCE OF LINGERING INHIBITION. THE ENSEMBLE SUITE
MAINTAINS A STUBBORN 25-100 J/KG OF SBCIN ACROSS THE WARM
SECTOR WELL INTO THE AFTERNOON. ADDITIONALLY, THIS THERMODYNAMIC
PROFILE MAY BE FURTHER MUDDIED BY THE REMNANTS OF THE MORNING
CONVECTION; SHOULD EXTENSIVE CLOUD DEBRIS OR REMNANT COLD POOLS
FAIL TO EFFECTIVELY MIX OUT DURING PEAK HEATING, THE SEVERE
THREAT COULD BE ENTIRELY ZAPPED. THUS, WHILE FORECASTER
CONFIDENCE REMAINS VERY HIGH THAT WIDESPREAD SHOWERS AND
THUNDERSTORMS WILL BLOSSOM AND EXPAND ACROSS CENTRAL ILLINOIS
LATE WEDNESDAY, THE EXACT MESOSCALE EVOLUTION AND THE CEILING OF
THE SEVERE THREAT REMAIN HIGHLY UNCERTAIN.
FROM A QPF STANDPOINT, LOCALIZED FLASH FLOODING MAY BECOME OUR
GREATEST CONCERN WEDNESDAY EVENING. RECENT HREF QPF LPMM
GUIDANCE SUPPORTS POCKETS OF UP TO 5 INCHES WHEREVER SHOWERS AND
THUNDERSTORMS TRAIN ALONG THE STALLED FRONT.
BY THURSDAY AND FRIDAY, MID-RANGE DETERMINISTIC GUIDANCE HAS
COME INTO TIGHTER ALIGNMENT, SUGGESTING THE SURFACE COLD FRONT
WILL LOSE ITS FORWARD MOMENTUM, WASHING OUT AND LINGERING ACROSS
CENTRAL AND SOUTHEASTERN ILLINOIS. THIS BOUNDARY WILL SERVE AS
A FOCUS FOR PROLONGED, OFF-AND-ON SHOWER AND THUNDERSTORM
CHANCES TO CLOSE OUT THE WORKWEEK. FORTUNATELY, WITH THE BEST
UPPER-LEVEL KINEMATICS AND STRONGER FLOW DEPARTING EASTWARD,
POOR DEEP-LAYER BULK SHEAR WILL PRECLUDE ANY ORGANIZED SEVERE
WEATHER THREAT THROUGH FRIDAY.
LONG TERM /SATURDAY THROUGH EARLY NEXT WEEK/
AS WE TRANSITION INTO THE WEEKEND, THE BROADER SYNOPTIC PATTERN
SUPPORTS A RETURN TO DRIER CONDITIONS BY SATURDAY. SUBSIDENCE
WILL OVERSPREAD THE REGION IN THE WAKE OF THE DEPARTING MID-WEEK
TROUGH, ALLOWING A PROMINENT, ANOMALOUS UPPER-LEVEL HEAT RIDGE
CURRENTLY ANCHORED TO OUR WEST TO EXPAND EASTWARD INTO THE MID-
MISSISSIPPI RIVER VALLEY.
WITH RISING MID-LEVEL HEIGHTS, UNCOMFORTABLE SUMMERTIME HEAT IS
POISED TO MAKE A RETURN. HIGH TEMPERATURES ARE FORECAST TO PUSH
BACK INTO THE LOW 90S. FACTORING IN THE POOLING OF REMNANT
BOUNDARY LAYER MOISTURE, HEAT INDEX VALUES WILL LIKELY CREEP
BACK TOWARD THE 100-DEGREE MARK BY SUNDAY AND EARLY NEXT WEEK.
HOWEVER, A MAJOR CAVEAT ACCOMPANIES THIS HEAT FORECAST. OUR
POSITION ON THE NORTHEAST PERIPHERY OF THE EXPANDING UPPER RIDGE
WILL PLACE CENTRAL ILLINOIS IN A CLASSIC RING OF FIRE REGIME.
NORTHWEST FLOW ALOFT WILL LEAVE THE DOOR WIDE OPEN FOR SUBTLE,
DIFFICULT-TO-TIME MID-LEVEL SHORTWAVES TO CREST THE RIDGE AND
DIVE SOUTHEASTWARD INTO THE REGION. THIS PATTERN IS NOTORIOUS
FOR BREEDING NOCTURNAL AND EARLY-DAY MESOSCALE CONVECTIVE
SYSTEMS (MCSS). SHOULD THESE THUNDERSTORM COMPLEXES MATERIALIZE,
THE ASSOCIATED PRECIPITATION AND CONVECTIVE CLOUD DEBRIS WOULD
EASILY THWART THE INTENSE HEAT FORECAST. AT THIS RANGE, ENSEMBLE
AND MULTI-MODEL GUIDANCE DEPICT CONSIDERABLY MORE NOISE THAN
SIGNAL REGARDING THESE CONVECTIVE CHANCES, MEANING TEMPERATURE
TRENDS EARLY NEXT WEEK WILL BE HEAVILY--AND FRUSTRATINGLY--
DEPENDENT ON MESOSCALE CONVECTIVE EVOLUTION.
AVIATION /00Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 624 PM CDT TUE AUG 4 2026
VFR CONDITIONS ARE FORECAST THROUGH A MAJORITY OF THE TAF PERIOD. A
DECAYING LINE OF THUNDERSTORMS MAY IMPACT KPIA WEDNESDAY MORNING
WITH HIGHER CHANCES FOR SHOWERS AND STORMS ARRIVING DURING THE
AFTERNOON ALONG A COLD FRONT. ACTIVITY SHOULD HOLD OFF FROM EASTERN
AIRFIELDS (KDEC, KCMI) UNTIL CLOSER TO OR SHORTLY AFTER 00Z.
SOUTHERLY WINDS BECOMING VARIABLE AT TIMES WILL REMAIN LIGHT THE
NEXT 24 HOURS, WITH SPEEDS FORECAST TO REMAIN BELOW 10 KTS.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...NMA
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