689
FXUS63 KILX 170504
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1204 AM CDT FRI APR 17 2026
KEY MESSAGES
- THERE IS AN ENHANCED RISK (LEVEL 3 OF 5) OF SEVERE
THUNDERSTORMS NEAR AND WEST OF THE ILLINOIS RIVER FRIDAY
AFTERNOON-EVENING. A SLIGHT RISK (LEVEL 2 OF 5) EXTENDS FROM
THE IL RIVER TO A SHELBYVILLE-DANVILLE LINE. DAMAGING WINDS,
LARGE HAIL, AND TORNADOES ARE ALL POSSIBLE.
- LOW TEMPERATURES IN THE 30S COULD LEAD TO FROST DEVELOPING
BOTH SATURDAY NIGHT AND SUNDAY NIGHT. THIS COULD HARM ANY
SENSITIVE EARLY SEASON VEGETATION.
DISCUSSION
ISSUED AT 214 PM CDT THU APR 16 2026
*** REST OF TODAY ***
MOSTLY SUNNY ACROSS IL THIS AFTERNOON, SAVE FOR SOME CORRIDORS
OF SCATTERED DIURNAL CUMULUS. TEMPS REMAIN ABOVE NORMAL ONCE
AGAIN, WITH SFC TEMPS IN THE LOW/MID 70S AS OF 18Z/1PM AND THE
EXPECTATION BEING THESE WILL CLIMB INTO THE UPPER 70S THIS
AFTERNOON. IL SITS BETWEEN A FEW SFC FEATURES INCLUDING A
1006-MB SFC LOW OVER THE GREAT LAKES AND A 1022-MB SFC HIGH OVER
THE SE CONUS.
A SUBTLE SHORTWAVE LIFTING ACROSS THE OZARKS IS INTERACTING WITH
MODEST INSTABILITY (1000-2000 J/KG OF SBCAPE), WHICH HAS LED TO
SCATTERED THUNDERSTORMS DEVELOPING. EFFECTIVE SHEAR VALUES ARE UNDER
30 KTS. THIS ACTIVITY IS PROGGED TO STAY JUST SOUTH OF THE ILX CWA,
BUT FELT IT WORTH A MENTION SINCE IT WILL BE A CLOSE CALL ALONG THE
US-50 CORRIDOR. A MARGINAL RISK (LEVEL 1 OF 5) OF SEVERE STORMS WAS
ADDED FOR AREAS SOUTH OF I-64, MAINLY FOR HAIL POTENTIAL WITH THESE
STORMS. THESE STORMS SHOULD PUSH OUT OF IL BY 02-03Z/9-10PM CT.
EXPECT MOSTLY CLEAR SKIES AND MILD TEMPS TONIGHT, WITH LOWS IN THE
MID 50S (NEARLY 10-15 DEGREES ABOVE NORMAL).
*** FRIDAY SEVERE STORM POTENTIAL ***
THE BIGGEST CHANGE TO HIGHLIGHT FOR FRIDAY'S SEVERE STORMS IS A
TREND TOWARDS FASTER/EARLIER TIMING. AN UPPER TROUGH, CURRENTLY
EVIDENT IN IR SATELLITE IMAGERY OVER MONTANA, WILL RESULT IN LEE
CYCLOGENESIS TONIGHT. INTO FRI, GUIDANCE DEPICTS A SFC LOW OVER
NORTHERN MN WITH A COLD FRONT EXTENDING SOUTH-SOUTHWEST INTO
KS. THE ILX CWA WILL BE FIRMLY WITHIN THE EXPANSIVE WARM SECTOR
OF THIS SYSTEM, WHERE BREEZY SOUTH WINDS WILL ADVECT HIGHER
MOISTURE CONTENT, WITH SFC DEWPOINTS IN THE LOW/MID 60S. THE
RESULTANT INSTABILITY VALUES WILL BE HIGH, RANGING FROM
2000-3000+ J/KG (INCREASING WITH NW EXTENT).
FORECAST SOUNDINGS SHOW ONLY MINIMAL CAPPING REMAINING BY EARLY
AFTERNOON, AND THE LATEST CAMS SEEM TO BE LATCHING ONTO A PRE-
FRONTAL TROUGH NW OF THE IL RIVER AS AN INITIATING BOUNDARY.
WHILE SFC CONVERGENCE LOOKS UNINSPIRING, ONLY HAVING WEAK
CAPPING IN PLACE DOES LEND CREDENCE TO THE CAM SOLUTIONS
DEPICTING STORM DEVELOPMENT EARLIER THAN PREVIOUSLY FORECAST
(POTENTIALLY AS EARLY AS 20Z/3PM). FORECAST HODOGRAPHS APPEAR
QUITE SUPPORTIVE OF LARGE HAIL, CONDITIONAL UPON A SUPERCELLULAR
STORM MODE, WITH MUTED LOW-LEVEL SHEAR (0-1 KT SHEAR LESS THAN
15 KTS) AND A STRAIGHT, ELONGATED HODOGRAPH THROUGH THE MID-
LEVELS. HOWEVER, WITH LINEAR FORCING, WEAK CAPPING, AND RIGHT-
MOVING SUPERCELL STORM MOTIONS NEARLY PARALLEL TO THE INITIATING
BOUNDARY, THE EXPECTATION IS THAT QUICK UPSCALE GROWTH WILL
OCCUR WHICH WOULD LIMIT THE LARGE HAIL POTENTIAL TO SOME DEGREE
AND INSTEAD FAVOR A DAMAGING WIND/LINE-EMBEDDED TORNADO THREAT.
THE WINDOW FOR ANY SUPERCELLS WOULD BE AS STORMS INITIALLY FORM
DURING THE AFTERNOON NW OF THE IL RIVER. WHILE ANY SUPERCELL
WILL BE CAPABLE OF PRODUCING TORNADOES, THE SUPERCELL TORNADO
THREAT IS HIGHEST NNW OF THE ILX CWA, CLOSER TO THE SFC LOW
WHERE BACKED SFC WINDS AND HIGHER LOW-LEVEL HELICITY WILL BE
PRESENT.
BY MID-EVENING, CAMS ALMOST UNIFORMLY DEPICT A LINEAR STORM
MODE, NEARING THE IL RIVER BY 00Z/7PM. BY THAT TIME, THE LLJ
WILL BE RAMPING UP, LEADING TO A CONSIDERABLE INCREASE IN 0-1 KM
SHEAR (30+ KTS) AND STORM-RELATIVE HELICITY (300+ J/KG). THESE
CONDITIONS COULD SUPPORT STRONG LINE-EMBEDDED TORNADOES, BUT
WILL LIKELY REQUIRE LOCALIZED SURGES/BOWS WITHIN THE LINE TO
OBTAIN A FAVORABLE SHEAR VECTOR ORIENTATION FOR MESOVORT
DEVELOPMENT. THE SEVERE THREAT WILL GRADUALLY WANE INTO THE
NIGHT AS STORMS PROGRESS EAST, BUT BASED ON THE SLIGHTLY FASTER
STORM TIMING THE SLIGHT RISK (LEVEL 2 OF 5) WAS EXPANDED AS FAR
EAST AS A DANVILLE-SHELBYVILLE LINE, WITH A MARGINAL RISK
FURTHER EAST FROM THERE.
IN SUMMARY, THE THINKING IS STORM DEVELOPMENT BY MID-AFTERNOON
NW OF THE IL RIVER, WITH SUPERCELLS POSING A RISK OF ALL
HAZARDS. STORMS ARE EXPECTED TO QUICKLY GROW UPSCALE, WITH A
SQUALL LINE THEN BRINGING A RISK OF SCATTERED DAMAGING WINDS AND
EMBEDDED TORNADOES. LATEST MODEL GUIDANCE HAS THIS LINE OF
STORMS NEAR THE IL RIVER AT 00Z/7PM. STORMS ARE UNLIKELY TO
REACH AREAS EAST OF I-55 UNTIL AFTER 01-02Z/8-9PM. MONITOR
FORECAST UPDATES, AS THE SPECIFIC TIMING COULD STILL CHANGE BY A
FEW HOURS.
*** FROST/FREEZE POTENTIAL THIS WEEKEND ***
FOLLOWING FROPA ON SAT AND THE DEPARTURE OF PRECIP, THE MAIN
CONCERN WILL BE A COLDER AIRMASS OFFERING FROST/FREEZE
POTENTIAL. AN EXPANSIVE SFC HIGH WILL BE PRESENT OVER THE PLAINS
SAT NIGHT, THEN SHIFT EAST TOWARDS THE NORTHERN OHIO VALLEY SUN
NIGHT. MOSTLY CLEAR SKIES AND LIGHT WINDS SHOULD ALLOW LOWS TO
FALL INTO THE 30S. THE PROBABILITY OF FROST OR FREEZE INCREASE
WITH NORTHWARD EXTENT, BUT ANYONE WITH SENSITIVE VEGETATION WILL
NEED TO BE PREPARED TO TAKE ACTION THIS WEEKEND. FOR SATURDAY
NIGHT, THE PROBABILITY OF LOWS BELOW 36F IS 60-80% NORTH OF A
MACOMB-BLOOMINGTON LINE, DECREASING TO 20-40% ALONG AND SOUTH OF
I-72. FOR SUNDAY NIGHT, THE PROBABILITY OF TEMPS BELOW 36F IS
70-80% ALONG THE I-74 CORRIDOR, DECREASING TO 30-40% ALONG THE
I-70 CORRIDOR. THE PROBABILITY OF A FREEZE IS LOWER, BELOW 50%
AREA-WIDE BOTH NIGHTS. WHILE NOT IMPACTFUL, HIGHS WILL ALSO BE
COOLER OVER THE WEEKEND, IN THE 50S OR LOW 60S.
*** TRENDING WARMER NEXT WEEK ***
INTO NEXT WEEK, TEMPS REBOUND WITH HIGHS BACK INTO THE 70S. THE
UPPER PATTERN WILL BE CHARACTERIZED BY NW FLOW LOCALLY, WITH
UPPER DISTURBANCES PASSING BY TO OUR NORTH. ELSEWHERE, HEIGHT
RISES START TO BUILD OVER THE WESTERN PLAINS AHEAD OF A CUT-OFF
LOW OFF THE WEST COAST. WITH SOME WEAKER DISTURBANCES POSSIBLE
WITHIN THE NW FLOW REGIME, LIGHT PRECIP CHANCES CAN'T BE RULED
OUT NEXT WEEK, BUT THERE ISN'T AN OVERWHELMING SIGNAL TO LATCH
ONTO AT THIS RANGE AND THE BLENDED GUIDANCE KEPT POPS BELOW 15%
MON-WED. THE EXTENDED RANGE OUTLOOK (DAYS 8-14) CONTINUES TO
FAVOR ABOVE NORMAL PRECIP ACROSS IL (33-50% CHANCE).
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 1203 AM CDT FRI APR 17 2026
LOW PRESSURE WILL LIFT ACROSS THE UPPER MIDWEST FRIDAY AFTERNOON
THROUGH FRIDAY NIGHT WITH A TRAILING COLD FRONT SWEEPING ACROSS
CENTRAL ILLINOIS FRIDAY NIGHT. WELL AHEAD OF THE FRONT, VFR
CONDITIONS AND BREEZY SOUTH WINDS WILL PREVAIL THOROUGH THE DAY
FRIDAY, WITH GUSTS INCREASING INTO THE 20-30 KT RANGE DURING THE
AFTERNOON AND EVENING. A LINE OF THUNDERSTORMS WILL PRECEDE THE
COLD FRONT MOVING ACROSS CENTRAL ILLINOIS MID TO LATE IN THE
EVENING WITH FRONTAL PASSAGE EXPECTED NEAR THE END OR JUST
BEYOND THE CURRENT VALID PERIOD.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...MJA
DISCUSSION...ERWIN
AVIATION...DEUBELBEISS
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