375
FXUS63 KILX 171826
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
126 PM CDT FRI JUL 17 2026
KEY MESSAGES
- HIGH TEMPERATURES AND HUMIDITY WILL BRING HEAT INDEX VALUES
BETWEEN 100 AND 105 DEGREES SATURDAY AFTERNOON. THERE IS A
30% TO 50% CHANCE FOR HEAT INDEX VALUES TO EXCEED 105 DEGREES
WEST OF INTERSTATE 55.
- THUNDERSTORMS WILL BRING A RISK OF LOCALIZED HEAVY RAINFALL
EXCEEDING 2 INCHES THIS AFTERNOON. ON SATURDAY AFTERNOON AND
EVENING, A PASSING COLD FRONT BRINGS A THREAT FOR SEVERE
STORMS.
- WILDFIRE SMOKE WILL MOVE INTO THE REGION FROM THE NORTH AFTER
MIDNIGHT SATURDAY NIGHT. EXPECT SMOKE TO IMPACT MOST OF
CENTRAL ILLINOIS BY SUNDAY AFTERNOON.
DISCUSSION
ISSUED AT 120 PM CDT FRI JUL 17 2026
SYNOPTIC OVERVIEW...
SURFACE ANALYSIS THIS AFTERNOON DEPICTS HIGH PRESSURE CENTERED
OVER THE LOWER MISSISSIPPI VALLEY, WITH A RIDGE AXIS EXTENDING
NORTHEAST INTO THE APPALACHIANS. ALOFT, A ROBUST 590 DAM HIGH
REMAINS ANCHORED OVER THE DESERT SOUTHWEST, MAINTAINING A
PERSISTENT NORTHWEST FLOW PATTERN DOWNSTREAM ACROSS THE GREAT
LAKES REGION.
HEAT AND HUMIDITY...
NEAR-TERM CONCERNS CONTINUE TO FOCUS ON A PERIOD OF BUILDING
HEAT AND HUMIDITY. AN 850MB THERMAL RIDGE OF 20-25C WILL SHIFT
FROM THE NORTHERN GREAT PLAINS INTO CENTRAL ILLINOIS BY
SATURDAY. FOLLOWING DAYTIME HIGHS NEAR 90F TODAY, TEMPERATURES
ARE EXPECTED TO REACH THE LOW 90S ON SATURDAY. WITH DEW POINTS
REMAINING IN THE LOW TO MID-70S, PEAK HEAT INDICES ARE PROJECTED
BETWEEN 100-105F SATURDAY AFTERNOON. HREF PROBABILITIES FOR
EXCEEDING 105F HEAT INDICES ARE 30-50% ALONG AND WEST OF I-55,
WITH LOWER PROBABILITIES TO THE EAST. AT THIS JUNCTURE,
CONFIDENCE IN REACHING HEAT ADVISORY CRITERIA IS INSUFFICIENT
FOR HEADLINES, THOUGH TRENDS WILL BE CLOSELY MONITORED SHOULD
HEAT POTENTIAL INCREASE.
CONVECTIVE OUTLOOK...
FOR THIS AFTERNOON AND EVENING, MODERATE INSTABILITY WITH
MLCAPE VALUES NEAR 2000 J/KG IS PRESENT. IN THE ABSENCE OF
STRONG LARGE-SCALE FORCING AND GIVEN WEAK DEEP-LAYER SHEAR
(<15KT), THE SEVERE THREAT REMAINS LOW. ISOLATED TO WIDELY
SCATTERED THUNDERSTORMS ARE POSSIBLE DURING PEAK HEATING. SLOW
STORM MOTIONS (LESS THAN 15 MPH) PRESENT A RISK FOR LOCALIZED
HEAVY RAIN, WITH HREF LPMM GUIDANCE HIGHLIGHTING POTENTIAL
POCKETS OF RAINFALL EXCEEDING 2 INCHES.
ON SATURDAY, A ROBUST SHORTWAVE TROUGH IS EXPECTED TO DIG
ACROSS THE GREAT LAKES, DRIVING A COLD FRONT SOUTH THROUGH
NORTHERN AND CENTRAL ILLINOIS. THIS BOUNDARY WILL INTERACT WITH
STRONG INSTABILITY, WITH MLCAPE PROGGED TO EXCEED 3000 J/KG.
WHILE DEEP-LAYER SHEAR REMAINS MARGINAL (25KT), THE FRONTAL
TIMING APPEARS FAVORABLE FOR PEAK DIURNAL HEATING, SUPPORTING
THE POTENTIAL FOR STRONGER STORM DEVELOPMENT SATURDAY AFTERNOON
AND EVENING. GUIDANCE HAS SLOWED SLIGHTLY REGARDING FRONTAL
ARRIVAL, AND THE SEVERE THREAT APPEARS MORE FOCUSED NORTH OF
SPRINGFIELD TO PARIS LINE A RESULT.
EXTENDED FORECAST...
THE COLD FRONT WILL SETTLE ALONG THE OHIO VALLEY SUNDAY, AS
HIGH PRESSURE BUILDS ACROSS THE GREAT LAKES IN ITS WAKE. THIS
TRANSITION WILL PROVIDE A BRIEF WINDOW OF NEAR-NORMAL
CONDITIONS, WITH HIGHS IN THE MID-80S AND SLIGHTLY LOWER
HUMIDITY LEVELS AS DEW POINTS DIP INTO THE UPPER 60S TO LOWER
70S. THE BOUNDARY IS EXPECTED TO LIFT BACK NORTH ACROSS THE
REGION ON MONDAY, SERVING AS A FOCUS FOR ADDITIONAL STORMS.
WHILE PLACEMENT UNCERTAINTY REMAINS, A STRENGTHENING LOW-LEVEL
JET MONDAY EVENING SHOULD AID IN INCREASING STORM COVERAGE, WITH
SHEAR AND INSTABILITY PARAMETERS APPEARING SUPPORTIVE OF SEVERE
WEATHER POTENTIAL. A TRAILING COLD FRONT WILL PUSH ACROSS
CENTRAL ILLINOIS MONDAY NIGHT INTO TUESDAY MORNING; WHILE
DIURNAL TIMING IS LESS FAVORABLE FOR MUCH OF THE AREA, WE WILL
MONITOR FOR POTENTIAL REDEVELOPMENT ALONG THE FRONT IN
SOUTHEASTERN COUNTIES ON TUESDAY. BY MID-WEEK, A STRONGER
CANADIAN HIGH-PRESSURE SYSTEM WILL BUILD SOUTH ACROSS THE
NORTHERN GREAT PLAINS AND UPPER MIDWEST, USHERING IN DRIER,
SLIGHTLY BELOW-NORMAL CONDITIONS FOR THE LATTER HALF OF THE
WEEK.
WILDFIRE SMOKE...
CANADIAN AND UPPER MIDWEST WILDFIRE ACTIVITY CONTINUES TO
PRODUCE A SIGNIFICANT SMOKE PLUME ACROSS THE GREAT LAKES INTO
THE MID-ATLANTIC COAST. CURRENT HRRR NEAR-SURFACE SMOKE GUIDANCE
INDICATES THE SOUTHERN EDGE OF THIS PLUME WILL SHIFT NORTH AWAY
FROM THE LOCAL AREA TODAY. BEHIND SATURDAY'S COLD FRONT, THE
ENVIRONMENT WILL BECOME MORE FAVORABLE FOR SMOKE ADVECTION INTO
CENTRAL ILLINOIS. REFS NEAR-SURFACE SMOKE GUIDANCE SUGGESTS
SMOKE MAY BEGIN TO SPREAD ACROSS THE REGION FROM THE NORTH AFTER
MIDNIGHT SATURDAY NIGHT, POTENTIALLY COVERING MOST OF CENTRAL
ILLINOIS BY LATE SUNDAY MORNING OR EARLY AFTERNOON, ALBEIT AT
CONCENTRATIONS MUCH LOWER THAN WE ARE CURRENTLY OBSERVING TO OUR
NORTH TODAY.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 1222 PM CDT FRI JUL 17 2026
ISOLATED TO WIDELY SCATTERED SHOWERS AND STORMS ARE EXPECTED
THIS AFTERNOON AND EVENING, THOUGH LOW COVERAGE AND CONFIDENCE
OF IMPACTS ON STATION PRECLUDES MORE THAN A PROB30. LIGHT
SOUTHWEST WINDS LESS THAN 10 KT TODAY AND TONIGHT WILL VEER TO
WESTERLY SATURDAY AND INCREASE INTO THE 10-12 KT RANGE. OUTSIDE
OF PRECIP, VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...DEUBELBEISS
DISCUSSION...DEUBELBEISS
AVIATION...DEUBELBEISS
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