730
FXUS63 KILX 131042
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
542 AM CDT SUN SEP 13 2026
KEY MESSAGES
- A SHARP TEMPERATURES GRADIENT IS EXPECTED ACROSS CENTRAL
ILLINOIS TODAY; HIGHS RANGE FROM THE 70S NORTHWEST OF I-55 TO
NEAR 90 SOUTH OF I-70.
- ISOLATED SHOWERS ARE POSSIBLE THIS AFTERNOON AND EVENING,
PRIMARILY WEST OF I-55, WITH LOCALIZED RAINFALL AROUND 0.10
INCHES.
- AN UNSETTLED PATTERN ARRIVES TUESDAY INTO WEDNESDAY WITH
WIDESPREAD SHOWERS, THUNDERSTORMS, HEAVY RAINFALL POTENTIAL,
AND A 5-15% CHANCE FOR SEVERE WEATHER.
DISCUSSION
ISSUED AT 216 AM CDT SUN SEP 13 2026
TODAY AND TONIGHT...
EARLY THIS MORNING, A COLD FRONT HAS PUSHED ACROSS MOST OF
CENTRAL ILLINOIS AND CURRENTLY LINGERS NEAR THE I-70 CORRIDOR.
TO THE NORTHWEST, HIGH PRESSURE IS CENTERED OVER THE DAKOTAS
WITH RIDGING EXTENDING SOUTHEAST INTO PORTIONS OF CENTRAL
ILLINOIS. A SHARP TEMPERATURE GRADIENT WILL BE IN PLACE ACROSS
THE REGION TODAY ACROSS THE STALLED FRONTAL ZONE. HIGHS
NORTHWEST OF THE I-55 CORRIDOR ARE PROJECTED TO TOP OUT IN THE
70S, WHEREAS LOCATIONS SOUTH OF I-70 WILL WARM TO AROUND THE 90
DEGREE MARK.
UNDERNEATH A STRONG MID-LEVEL (700-800 MB) WARM NOSE, SURFACE-
BASED INSTABILITY WILL BE VIRTUALLY NON-EXISTENT THIS AFTERNOON.
HOWEVER, MODEST ELEVATED INSTABILITY (700-1000 J/KG) ROOTED
ABOVE THE CAP, COMBINED WITH SUBTLE ISENTROPIC ASCENT ALONG THE
310-315K SURFACES, MAY ALLOW ONGOING ELEVATED SHOWERS AND WEAK
CONVECTION OVER IOWA AND MISSOURI EARLY THIS MORNING TO TRACK
INTO CENTRAL ILLINOIS DURING THE AFTERNOON HOURS. FORCING
REMAINS FAIRLY NEBULOUS, AND NBM MEAN 24-HOUR QPF HAS TRENDED
CONSIDERABLY DOWNWARD OVER THE PAST COUPLE RUNS, SHOWING AROUND
A TENTH OF AN INCH OF RAIN WEST OF I-55 WITH LESSER AMOUNTS
FURTHER EAST. HREF LPMM GUIDANCE SUPPORTS LOCALIZED AMOUNTS
AROUND 0.10 INCHES.
PRECIPITATION CHANCES WILL DIMINISH OVERNIGHT AS FORCING SHIFTS
BACK WEST TOWARD THE MID-MISSOURI VALLEY ON THE NOSE OF A LOW-
LEVEL JET. CONVECTION IS EXPECTED TO REMAIN WEST OF THE LOCAL
AREA THROUGH DAYBREAK. LOW TEMPERATURES TONIGHT WILL FALL INTO
THE MID-50S TO LOWER 60S UNDER LIGHT NORTH TO NORTHEAST WINDS
AND LINGERING CLOUD COVER.
MONDAY THROUGH WEDNESDAY...
AN ACTIVE AND UNSETTLED PATTERN IS ANTICIPATED THROUGH THE
FIRST HALF OF THE UPCOMING WORK WEEK. A CLOSED UPPER-LEVEL LOW
OVER THE PACIFIC NORTHWEST WILL TREK ACROSS THE CANADIAN ROCKIES
LATE TONIGHT INTO MONDAY. IN RESPONSE, A DEEP SURFACE LOW WILL
MATURE AND TRACK FROM THE CANADIAN PRAIRIES TOWARD HUDSON BAY
MONDAY INTO TUESDAY, DRAGGING A COLD FRONT INTO THE MIDWEST.
WIDESPREAD SHOWERS AND THUNDERSTORMS WILL ARRIVE ALONG THE
TRAILING COLD FRONT TUESDAY INTO WEDNESDAY. SEVERE WEATHER
POTENTIAL WARRANTS CLOSE MONITORING: THE UPPER-LEVEL JET DIPPING
ACROSS THE UPPER MIDWEST WILL ENHANCE DEEP-LAYER BULK SHEAR
(30-40 KT) OVER CENTRAL ILLINOIS. GFS GUIDANCE ADVERTISES
1000-1500 J/KG MLCAPE NEAR THE STALLING FRONTAL BOUNDARY,
WHICH WHEN COMBINED WITH THE FAVORABLE SHEAR SUPPORTS ORGANIZED
CONVECTIVE THREATS. CSU MACHINE LEARNING PROBABILITIES HIGHLIGHT
A 5-15% RISK FOR SEVERE WEATHER ACROSS CENTRAL ILLINOIS BOTH
DAYS AND SPC HAS INTRODUCED A MARGINAL RISK FOR MUCH OF THE AREA
ALONG AND NORTH OF I-70.
IN ADDITION TO SEVERE WEATHER, HEAVY RAINFALL WILL BE A PRIMARY
CONCERN AS MULTIPLE ROUNDS OF CONVECTION TRACK EASTWARD ALONG
THE SLOW-MOVING WEST-TO-EAST ORIENTED FRONT. THROUGH WEDNESDAY
NIGHT, NBM MEAN 48-HOUR QPF INDICATES 1.00 INCH OF RAINFALL
NORTH OF A BEARDSTOWN TO BLOOMINGTON LINE, WITH 2.00-INCH QPF
CONTOURS CLIPPING FAR NORTHWESTERN SECTIONS NEAR GALESBURG.
THURSDAY AND FRIDAY...
UNSETTLED CONDITIONS LOOK TO PERSIST INTO LATE NEXT WEEK AS THE
BAROCLINIC ZONE REMAINS DRAPED ACROSS THE REGION, SERVING AS A
FOCUS FOR DAILY PRECIPITATION CHANCES. MODEL GUIDANCE EXHIBITS
NOTABLE VARIANCE REGARDING FRONTAL PLACEMENT. THE GFS BUILDS A
STRONGER SURFACE HIGH BEHIND THE FRONT, SHUNTING THE BOUNDARY
SOUTH OF THE OHIO VALLEY BY LATE THURSDAY AND BRINGING COOLER,
DRIER CONDITIONS. CONVERSELY, THE ECMWF FEATURES A WEAKER, MORE
PROGRESSIVE RIDGE, KEEPING THE FRONTAL BOUNDARY STALLED ACROSS
CENTRAL AND NORTHERN ILLINOIS WITH CONTINUED CONVECTIVE CHANCES
AND A PERSISTENT THERMAL GRADIENT. GIVEN THESE DISCREPANCIES,
BROAD-BRUSHED CHANCE POPS REMAIN IN THE FORECAST WITH LOW
CONFIDENCE IN TEMPERATURES WHICH WILL BE HIGHLY DEPENDENT ON THE
EVENTUAL FRONTAL PLACEMENT.
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 542 AM CDT SUN SEP 13 2026
HIGH PRESSURE IS CENTERED OVER THE DAKOTAS EARLY THIS MORNING
AND WILL DRIFT EAST ACROSS THE UPPER MIDWEST TODAY. LIGHT
NORTHWEST WINDS EARLY THIS MORNING WILL GRADUALLY VEER TO THE
NORTH THEN NORTHEAST TODAY AS A RESULT. MEANWHILE, WARM AIR
ADVECTION DRIVEN SHOWERS AND A FEW STORMS WILL FORM OVER IOWA
AND MISSOURI TODAY AND DRIFT INTO CENTRAL ILLINOIS THIS
AFTERNOON AND EVENING IN A DECAYING STATE. THEY SHOULD BE HIGH
BASED AND MUCH WILL EVAPORATE IN THE DRY LOW LEVEL NORTHERLY
FLOW BEFORE REACHING THE SURFACE. AS SUCH, CONFIDENCE IN ANY
IMPACTS TO CEILINGS OR VISIBILITY REMAINS LOW.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...DEUBELBEISS
DISCUSSION...DEUBELBEISS
AVIATION...DEUBELBEISS
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