994
FXUS63 KILX 190516
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1216 AM CDT SAT SEP 19 2026
KEY MESSAGES
- UNSEASONABLE HEAT & TEMPERATURE CONTRAST: AREAS SOUTH OF THE
FRONT WILL SEE HEAT INDICES NEAR 100 F THROUGH SATURDAY. THIS
IS PRIMARILY NEAR AND SOUTH OF INTERSTATE 72.
- THUNDERSTORMS & MICROBURST RISK: SCATTERED SHOWERS AND STORMS
ARE FORECAST THROUGH SUNDAY. ON SATURDAY, STRONGER STORMS
COULD PRODUCE LOCALIZED DAMAGING WIND GUSTS UP TO 60 MPH AND
QUARTER-SIZED HAIL.
- SIGNIFICANTLY COOLER NEXT WEEK: HIGH CONFIDENCE THAT THE HOT
AIR WILL BE PUSHED SOUTH BY MONDAY. EXPECT COMFORTABLE, DRY
CONDITIONS WITH HIGHS IN THE UPPER 60S TO MID-70S AREAWIDE
TUESDAY THROUGH FRIDAY.
DISCUSSION
ISSUED AT 1231 PM CDT FRI SEP 18 2026
AN ANOMALOUS 594-MB HEAT RIDGE CONTINUES TO HOLD FIRM OVER THE
CENTRAL U.S. EARLY THIS AFTERNOON. POSITIONED ALONG THE NORTHERN
PERIPHERY OF THIS HEAT DOME, A WEAK SURFACE LOW RESTS NEAR
SIOUX CITY, IOWA, WITH AN ASSOCIATED WARM FRONT STRETCHING
SOUTHEASTWARD THROUGH COLUMBIA, MISSOURI TOWARD TERRE HAUTE,
INDIANA.
AS WEAK SHORTWAVE ENERGY EJECTS OUT OF THE DESERT SOUTHWEST, IT
WILL RIDE OVER THE FRONTAL BOUNDARY, OFFERING SUFFICIENT
SYNOPTIC LIFT TO DRIVE SCATTERED SHOWER ACTIVITY TODAY. THESE
SHORTWAVES WILL ALSO PUSH THE FRONTAL SYSTEM SLIGHTLY NORTH
FROM TONIGHT INTO SATURDAY.
NEAR THE WARM FRONT, POOLING SURFACE DEWPOINTS IN THE LOWER 70S
WILL HELP SUPPORT MLCAPE AROUND 2000 J/KG, KEEPING THE
POTENTIAL FOR AN ISOLATED THUNDERSTORM IN PLACE. POOR MID-LEVEL
LAPSE RATES WILL LIMIT ANY SEVERE THREAT TODAY. HOWEVER, AS THE
FRONT DRIFTS NORTHWARD ON SATURDAY, INCREASING BULK SHEAR (2535
KTS) MAY COMPENSATE FOR THE WEAK LAPSE RATES, ALLOWING FOR
OCCASIONALLY ORGANIZED STORMS CAPABLE OF PRODUCING LOCALIZED
SEVERE MICROBURST WINDS AND QUARTER-SIZED HAIL. BRIEF HEAVY
DOWNPOURS RESULTING IN 1"/HR RATES ARE A LOW (10-20%)
PROBABILITY, BUT COULD ACCOMPANY THE MORE ORGANIZED CONVECTION.
THIS POTENTIAL IS BEST HIGHLIGHTED BY THE HREF LPMM QPF, WHICH
HINTS AT LOCALIZED AMOUNTS UP TO 1.5".
BEYOND THE SCATTERED SHOWERS AND ISOLATED STORM POTENTIAL
THROUGH SATURDAY, THE PRIMARY FORECAST DIFFICULTY CENTERS ON THE
SHARP TEMPERATURE CONTRAST ACROSS THE REGION. WITH THE BOUNDARY
DRAPED ACROSS CENTRAL ILLINOIS, LOCATIONS TO THE NORTH WILL BE
CAPPED IN THE 80S, WHEREAS AREAS TO THE SOUTH WILL CLIMB BACK
INTO THE 90S WITH HEAT INDICES APPROACHING 100 F. OUTFLOW FROM
PASSING PRECIPITATION COULD LEAD TO SHARP LOCAL VARIATIONS IN
TEMPERATURES THROUGH SATURDAY.
BY SUNDAY, MODEL GUIDANCE AND ENSEMBLE SUITES EXHIBIT HIGH
CONFIDENCE THAT A CLOSED UPPER-LEVEL TROUGH WILL TRACK EAST
ACROSS THE PLAINS AND INTO THE MID-MISSISSIPPI VALLEY BY MONDAY.
THIS SYSTEM WILL DISMANTLE THE HEAT RIDGE AND PUSH THE FRONTAL
BOUNDARY SOUTH AND EAST OF THE FORECAST AREA. IN ITS WAKE,
EXPANSIVE HIGH PRESSURE WILL SETTLE IN UNDER A BLOCKING SPLIT-
FLOW REGIME ALOFT, BRINGING A PERIOD OF DRIER AND SIGNIFICANTLY
COOLER CONDITIONS. DAYTIME HIGHS FROM TUESDAY THROUGH FRIDAY ARE
EXPECTED TO REMAIN IN THE UPPER 60S TO MID 70S.
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
ISSUED AT 1215 AM CDT SAT SEP 19 2026
LOW STRATUS HAS DEVELOPED ALONG PORTIONS OF THE I-74 CORRIDOR
TONIGHT, AND WHILE IT HAS SINCE LIFTED NORTH OF THE TERMINALS,
NEW PATCHES OF STRATUS ARE NOTED DEVELOPING SOUTH OF THE
TERMINALS ON SATELLITE IMAGERY. LOW STRATUS AS WELL AS SOME
PATCHY FOG SHOULD STAY CONFINED TO THE I-74 CORRIDOR OVERNIGHT
AND ARE NOT EXPECTED TO IMPACT SPI/DEC AT THIS TIME. MEANWHILE
STORMS ARE ONGOING OVER SOUTHERN WISCONSIN AND NORTHEASTERN
IOWA. STORMS ARE EXPECTED TO SPREAD SOUTHEAST INTO NORTHERN
ILLINOIS OVERNIGHT AND MAY APPROACH THE I-74 CORRIDOR MID
SATURDAY MORNING. EVEN IF STORMS END UP STAYING JUST NORTH OF
THE TERMINALS, AN OUTFLOW BOUNDARY MAY KICK SOUTH TURNING WINDS
NORTHEASTERLY FOR A COUPLE HOURS BEFORE S/SE FLOW RESUMES. ANY
LINGERING STRATUS SHOULD IMPROVE BACK TO VFR EARLY TO MID
AFTERNOON.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...DEUBELBEISS
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