342
FXUS63 KILX 250211
AFDILX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LINCOLN IL
911 PM CDT THU APR 24 2025
KEY MESSAGES
- SCATTERED SHOWERS AND STORMS WILL DEVELOP ON FRIDAY, WITH THE
GREATEST COVERAGE BEING ALONG A COLD FRONT FRIDAY AFTERNOON AND
EARLY EVENING. DURING THAT TIME, THERE IS A 60-70% CHANCE OF
PRECIP ALONG AND EAST OF I-55.
- ASIDE FROM A BRIEF COOLDOWN ON SATURDAY, WHEN HIGHS WILL ONLY BE
IN THE 60S, TEMPERATURES WILL GENERALLY BE WARM. HIGHS EARLY
NEXT WEEK ARE FORECAST TO BE IN THE LOW TO MID 80S.
- THERE IS A 40-60% CHANCE OF STORMS LATE MONDAY THROUGH TUESDAY
AS A COLD FRONT MOVES ACROSS THE REGION. SOME OF THESE STORMS
COULD BE SEVERE (15% CHANCE).
UPDATE
ISSUED AT 911 PM CDT THU APR 24 2025
UPDATES MADE TO POPS THIS EVENING FOR ISOLATED SHOWERS AND
THUNDERSTORMS IN SOUTHEAST IL AND NW IL AS SHORTWAVES IN THE OHIO
VALLEY REGION AND IA VICINITY IMPACT THESE AREAS. OTHERWISE,
OVERNIGHT, WE SHOULD SEE THE IA SHORTWAVE EDGE CLOSER, PROMOTING
INCREASING SHOWER/THUNDERSTORM ACTIVITY OVERNIGHT, AND LOWS
REACHING AROUND 60.
37
DISCUSSION
ISSUED AT 126 PM CDT THU APR 24 2025
*** THROUGH THIS WEEKEND ***
IT'S BEEN A WARM SPRING DAY ACROSS CENTRAL IL, WITH TEMPS CLIMBING
INTO THE UPPER 70S AND LOW 80S AS OF 1PM/18Z. A QUASI- STATIONARY
COLD FRONT EXTENDS FROM NEAR LINCOLN, NE ACROSS SOUTHERN IA AND
INTO NORTHERN IL. CAMS DEPICT A LAKE-ENHANCED SURGE PUSHING SE
THIS EVENING, AND IT COULD REACH AS FAR SOUTH AS I-74 LATE IN THE
EVENING (CLOSER TO 11PM/MIDNIGHT). THE ONLY NOTICEABLE IMPACT
WOULD BE A SHIFT TO NORTHEASTERLY WINDS (AS OPPOSED TO SOUTHERLY)
AND A MINOR TEMPERATURE REDUCTION OF A FEW DEGREES COMPARED TO
AREAS FURTHER SOUTH.
A WEAK SHORTWAVE LIFTING SLOWLY NORTHEAST FROM THE CENTRAL PLAINS
WILL AID SCATTERED SHOWER/STORM DEVELOPMENT ON FRI. IT WILL ALSO
INDUCE AN AREA OF BROAD, WEAK SFC LOW PRESSURE (MSLP ~ 1012 MB) THAT
HELPS PULL THAT AFOREMENTIONED QUASI-STATIONARY COLD FRONT ACROSS
OUR AREA. THE PRESENCE OF THIS FRONT AND THE UPPER LEVEL FORCING
SHOULD LEAD TO AN UPTICK IN SHOWER/STORM COVERAGE NEAR/AHEAD OF
THE FRONT (60-70% CHANCE OF PRECIP EAST OF I-55 FRIDAY PM). SOME
OF THE MORE BULLISH CAMS DEPICT MODERATE INSTABILITY (OVER 1000
J/KG OF SBCAPE), WHICH COULD SUPPORT AN ISOLATED STRONGER UPDRAFT
CAPABLE OF A LOCALIZED HAIL OR WIND THREAT, BUT WITH BULK SHEAR
LESS THAN 25 KNOTS AN ORGANIZED SEVERE WX THREAT APPEARS UNLIKELY.
PRECIP ACTIVITY SHOULD EXIT TO THE E/SE OF THE ILX CWA BY ABOUT
03Z (10 PM). NORTHERLY WINDS COULD BE A LITTLE BREEZY FOLLOWING
THE FRONTAL PASSAGE, WITH GUSTS GENERALLY 20-25 MPH.
FOLLOWING THE FRONTAL PASSAGE, SFC HIGH PRESSURE BUILDS IN TO THE
UPPER MIDWEST ON SATURDAY. LOCALLY, IT WILL BE COOLER WITH HIGHS
ONLY IN THE 60S. THE COOL DOWN WILL BE SHORT-LIVED, HOWEVER, AS THAT
SFC HIGH TRANSLATES EAST AND USHERS IN A RETURN OF SOUTHERLY FLOW BY
SUNDAY. HIGHS SHOULD RETURN TO THE 70S ON SUN, AND THEN INTO THE LOW
80S ON MON.
*** NEXT WEEK ***
AN AMPLIFIED TROUGH EJECTS ONTO THE PLAINS EARLY NEXT WEEK, AND THE
ASSOCIATED SFC LOW IS EXPECTED TO TRACK FROM THE CENTRAL PLAINS TO
THE UPPER MIDWEST. A COLD FRONT IS PROGGED TO MOVE ACROSS THE ILX
CWA SOMETIME LATE MON INTO TUES, POSING A RISK OF SEVERE STORMS AS
IT DOES. DURING THE DAYTIME HOURS, GUIDANCE SHOWS MODERATE-TO-HIGH
INSTABILITY DEVELOPING IN THE WARM SECTOR AHEAD OF THE FRONT (SBCAPE
OVER 2000 J/KG). THE BIG QUESTION FOR OUR SEVERE RISK LOCALLY IS THE
DIURNAL TIMING OF THE FRONT/STORMS. CURRENT GUIDANCE SUGGESTS STORMS
PUSHING INTO OUR NORTHWEST CWA LATE MON EVE, PERHAPS WEAKENING AS
THEY DO, AND THEN RENEWED DEVELOPMENT ACROSS THE SOUTHERN HALF OF
THE CWA ON TUES AS THE SYSTEM PROGRESSES. THE EXACT TIMING IS LIKELY
TO BE REFINED IN THE COMING DAYS.
THERE ARE SOME QUESTIONS ABOUT THE SEVERE THREAT INTO TUES AS THE
UPPER LOW STARTS TO LIFT AWAY FROM THE REGION, WEAKENING BOTH THE
LARGE SCALE ASCENT AND THE MID-LEVEL FLOW (WEAKER SHEAR). AN INITIAL
LOOK AT FORECAST SOUNDINGS/HODOGRAPHS FROM THE GFS FOR TUES SHOW
MODERATELY STEEP MID-LEVEL LAPSE RATES WITH UNIDIRECTIONAL LOW-LEVEL
WIND PROFILES. GIVEN THE EXPECTED FRONTAL FORCING AND A SHEAR VECTOR
CROSSING ANGLE OF LESS THAN 45DEG, CLUSTERS OR QUASI-LINEAR STORM
SEGMENTS APPEAR MORE LIKELY THAN DISCRETE CELLS. COLLECTIVELY, THESE
FEATURES SUGGEST HAIL/WIND THREATS WOULD BE THE MAIN CONCERNS ON
TUES. CONVERSELY, FOR THE NW PORTIONS OF THE ILX CWA LATE MON EVE,
THE CLOSER PROXIMITY TO THE SFC LOW WILL RESULT IN BETTER TURNING OF
THE LOW-LEVEL WINDS, MEANING ALL HAZARDS (HAIL/WIND/TORNADOES) WOULD
CONDITIONALLY BE SUPPORTED SHOULD SURFACE-BASED STORMS OCCUR. IN
SUMMARY, THERE IS A CHANCE (15%) FOR SEVERE STORMS ALONG A COLD
FRONT LATE MON NIGHT THROUGH TUES, WITH THE SVR CHANCES BEING HIGHER
IN AREAS WHERE STORMS OCCUR DURING THE AFTERNOON/EARLY EVENING.
AFTER THAT FRONT MOVES THROUGH, MUCH OF THE AREA SHOULD SEE A BREAK
FROM PRECIP AS SFC HIGH PRESSURE NOSES IN ONCE AGAIN. WILL HAVE TO
MONITOR THE SOUTHERN PARTS OF THE CWA, AS THE FRONT STALLS ACROSS
THE TN VALLEY, PERHAPS CLOSE ENOUGH TO KEEP LINGERING PRECIP AROUND.
THE BLENDED POPS SEEM TOO BROAD, KEEPING 15-30% CHANCES ACROSS THE
NORTHERN HALF OF THE ILX CWA THROUGH WED, PERHAPS OWING TO TIMING
DIFFERENCES. I EXPECT THESE POPS TO DECLINE AS WE GET CLOSER,
ASSUMING THE CURRENT FORECAST REMAINS ON TRACK. LATER IN THE WEEK
(THURS-FRI), ANOTHER SHORTWAVE LIFTS ACROSS THE SOUTHERN PLAINS,
TUGGING THAT FRONTAL ZONE AND ASSOCIATED PRECIP CHANCES (30-60%)
NORTHWARD BACK INTO THE ILX CWA.
ERWIN
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 622 PM CDT THU APR 24 2025
SCATTERED SHOWERS AND THUNDERSTORMS LOOK TO DEVELOP EARLY FRIDAY
MORNING, CONTINUING MUCH OF THE DAY, AS A COLD FRONT AND UPPER
LEVEL WAVE GRADUALLY WORK ACROSS THE AREA. THUNDERSTORMS LOOK TO
BE MOST PREVALENT NEAR/EAST OF I-55 DUE TO PROXIMITY OF BETTER
LIFT DURING BETTER DIURNAL HEATING, HOWEVER THUNDERSTORMS CAN'T BE
RULED OUT AFTER AROUND 10-12Z THROUGH THE END OF THE PERIOD.
GENERALLY VFR CONDITIONS ARE EXPECTED, HOWEVER STRONGER STORMS
COULD SEE LOCALIZED MVFR CIGS, AND MVFR OR WORSE VSBY. WINDS
GENERALLY LIGHT SOUTHERLY OVERNIGHT, SHIFTING TO NW BEHIND THE
FRONT AFTER 18Z-22Z, HOWEVER WILL NEED TO WATCH POTENTIAL FOR
WINDS SHIFTING TO LIGHT NE FOR A TIME LATE THIS EVENING AS A LAKE
MICHIGAN BREEZE ATTEMPTS TO PROPAGATE INTO THE KBMI AREA, PERHAPS
KCMI AS WELL.
37
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
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