599
FXUS63 KILX 260927
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
427 AM CDT SAT SEP 26 2026
KEY MESSAGES
- EXPECT MOSTLY DRY CONDITIONS AND MILD TEMPERATURES THROUGH
TUESDAY AFTERNOON, THOUGH A FEW LIGHT SHOWERS ARE POSSIBLE
WEST OF INTERSTATE 55 TODAY.
- HEAVY RAINFALL AND LOCALIZED FLOODING BECOME THE PRIMARY
CONCERN WEDNESDAY THROUGH FRIDAY AS REPEATED ROUNDS OF RAIN
MOVE ACROSS CENTRAL ILLINOIS.
- THERE IS A 25% TO 50% CHANCE OF RAINFALL EXCEEDING 2 INCHES
BETWEEN WEDNESDAY MORNING AND SATURDAY MORNING, WITH THE
HIGHEST AMOUNTS EXPECTED NORTHWEST OF THE ILLINOIS RIVER
VALLEY.
DISCUSSION
ISSUED AT 251 AM CDT SAT SEP 26 2026
AN EXPANSIVE UPPER-LEVEL BLOCKING PATTERN CONTINUES TO GOVERN
THE REGIONAL WEATHER REGIME, EFFECTIVELY SANDWICHING CENTRAL
ILLINOIS BETWEEN A DEEP COASTAL LOW (NOR'EASTER) TRACKING ALONG
THE MID-ATLANTIC/NEW ENGLAND SEABOARD AND A SHORTWAVE TROUGH
LIFTING NORTHWARD ACROSS THE GREAT PLAINS TOWARD THE UPPER
MISSISSIPPI VALLEY. MID-LEVEL MOISTURE ADVECTION ASSOCIATED WITH
THE WESTERN SHORTWAVE IS SPREADING EASTWARD INTO THE LOCAL
FORECAST AREA, THOUGH IT ENCOUNTERS A DEEPLY ENTRENCHED DRY SUB-
CLOUD LAYER ACROSS EASTERN ILLINOIS, WHERE GENTLE EASTERLY FLOW
CONTINUES TO ADVECT IN DEWPOINTS IN THE UPPER 40S.
SUBTLE MID-LEVEL CONVERGENCE ATOP THIS DRY BOUNDARY LAYER WILL
SUPPORT SCATTERED, HIGH-BASED SHOWERS THIS AFTERNOON AND
EVENING, PRIMARILY WEST OF INTERSTATE 55. WEAK ATMOSPHERIC FLOW
WILL RESULT IN SLOW-MOVING OR TRAINING CELL MOTION. THIS
PROLONGED RESIDENCE TIME OVER LOCALIZED CORRIDORS COULD
SUFFICIENTLY ERODE THE NEAR- SURFACE DRY AIR TO YIELD MEASURABLE
PRECIPITATION ACROSS OUR WESTERN COUNTIES.
HIGHS TODAY WILL FEATURE A CLOUD- AND PRECIP- DRIVEN GRADIENT,
RANGING FROM THE UPPER 60S WEST OF I-55 TO THE MID-70S EASTWARD
WHERE DRY AIR AND SUN PERSIST LONGER.
FOR MONDAY, PERSISTENT BLOCKING MAINTAINS GENERALLY TRANQUIL
CONDITIONS ACROSS THE REGION. EXPECT VARIABLE CLOUDINESS AND
OCCASIONAL LIGHT SPRINKLES, WITH SEASONABLE HIGH TEMPERATURES
HOLDING IN THE LOW-TO-MID 70S UNDER A LIGHT EASTERLY SURFACE
WIND.
THE BENIGN PATTERN WILL COLLAPSE RAPIDLY BY TUESDAY AS GLOBAL
GUIDANCE ALIGNS ON STRONG SHORTWAVE ENERGY EJECTING OUT OF THE
SOUTHWEST U.S. AHEAD OF A BROADER PARENT TROUGH. WARM AIR AND
MOISTURE ADVECTION AHEAD OF THIS SWIFT-MOVING FEATURE WILL BOOST
TUESDAY AFTERNOON HIGHS INTO THE UPPER 70S. AS THE ATTENDANT
COLD FRONT APPROACHES, ELEVATED ASCENT WILL SATURATE THE COLUMN,
BRINGING INCREASING RAIN CHANCES FROM WEST TO EAST TUESDAY
EVENING INTO WEDNESDAY AS THE FRONT SLOWLY CREEPS INTO CENTRAL
ILLINOIS.
HYDRO CONCERNS TAKE CENTER STAGE WEDNESDAY THROUGH FRIDAY AS
THE FRONTAL BOUNDARY DECELERATES AND BECOMES QUASI-STATIONARY
ACROSS THE FORECAST AREA, ORIENTING NEARLY PARALLEL TO THE
UPPER-LEVEL FLOW. GLOBAL DETERMINISTIC GUIDANCE STRONGLY FAVORS
THE SOUTHWESTERN UPPER TROUGH PHASING WITH TROPICAL DEPRESSION
POLO. THIS TROPICAL INTERACTION WILL TRANSPORT A DEEP RESERVOIR
OF MOISTURE NORTHWARD ALONG THE STALLED BAROCLINIC ZONE.
REPEATED ROUNDS OF RAINFALL LOOK INCREASINGLY PROBABLE
WEDNESDAY THROUGH FRIDAY AS THE CORE SHORTWAVE ADVANCES
SLUGGISHLY ALONG THE WAVERING FRONT. HIGH RAINFALL EFFICIENCY
AND TRAINING SHOWERS WILL MAKE LOCALIZED FLOODING OUR PRIMARY
CONCERN THROUGH LATE WEEK, AS WEAK INSTABILITY AND SHEAR
PARAMETERS KEEP THE SEVERE WEATHER THREAT LOW.
THE POTENTIAL FOR HEAVY RAINFALL IS WELL-REPRESENTED IN CURRENT
NBM PROBABILITIES, WHICH INDICATE A 25-50% CHANCE OF 72-HOUR
RAINFALL TOTALS EXCEEDING 2 INCHES BETWEEN WEDNESDAY MORNING AND
SATURDAY MORNING. THE HIGHEST PROBABILITY AXIS FAVORS AREAS
NORTHWEST OF THE ILLINOIS RIVER VALLEY, WITH LOWER PROBABILITIES
ANCHORED OVER SOUTHEAST ILLINOIS. PRECIPITATION CHANCES SHOULD
SLOWLY WANE INTO NEXT WEEKEND AS POLO COMPLETES ITS
EXTRATROPICAL TRANSITION AND THE MAIN TROUGH KICKS EAST.
AVIATION /12Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 424 AM CDT SAT SEP 26 2026
MID-LEVEL CLOUDS WILL INCREASE FROM WEST TO EAST ACROSS THE
REGIONAL TERMINALS TODAY. WHILE VFR CONDITIONS SHOULD PERSIST
THROUGH THE ENTIRE TAF PERIOD, THERE IS A LOW PROBABILITY FOR
SCATTERED, HIGH-BASED SHOWERS AT KSPI/KPIA THIS EVENING.
OTHERWISE, ANTICIPATE LOW-LEVEL WINDS TO MAINTAIN AN EAST
COMPONENT BETWEEN 5-8 KTS.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...MJA
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