870
FXUS63 KILX 201858
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
158 PM CDT SUN APR 20 2025
KEY MESSAGES
- THERE IS A LEVEL 2 OF 5 (SLIGHT) RISK FOR SEVERE WEATHER THIS
EVENING INTO TONIGHT. THE GREATEST RISK APPEARS TO BE FROM
DAMAGING WINDS, THOUGH TORNADOES AND HAIL ARE POSSIBLE AS WELL,
MAINLY WEST OF A JACKSONVILLE TO ALTONA LINE. MOST FAVORABLE
TIMING WOULD BE 6PM TO MIDNIGHT.
- THE RISK FOR FLOODING IS LOW (LESS THAN 10%), BUT THERE MAY BE
SOME LOCALIZED PONDING OF WATER IN TYPICAL POOR-DRAINAGE URBAN
AREAS.
- CHANCES FOR SHOWERS AND STORMS RETURN TOWARDS MIDWEEK. AT THIS
TIME, THE CHANCE FOR SEVERE WEATHER APPEARS LOW (LESS THAN 5%).
DISCUSSION
ISSUED AT 155 PM CDT SUN APR 20 2025
***** SEVERE WEATHER RISK THIS EVENING-TONIGHT *****
ALL ATTENTION REMAINS ON THE DEVELOPING UPSTREAM CONVECTION THIS
AFTERNOON. A COMPACT LOW PRESSURE SYSTEM IS FORECAST TO LIFT INTO
IOWA AND DRAG ITS ATTENDANT COLD FRONT ACROSS THE ILX CWA BETWEEN
ROUGHLY 9PM AND 3AM TONIGHT. ALONG AND AHEAD OF THAT FRONT, A LINE
OF INTENSE THUNDERSTORMS HAS ALREADY DEVELOPED UPSTREAM; THESE
STORMS WILL BE ON A WEAKENING TREND AS THEY ARRIVE IN THE PRAIRIE
STATE AROUND 7PM OWING TO LOSS OF DIURNALLY-DRIVEN SURFACE BASED
INSTABILITY, BUT STILL POSE SOME RISK FOR DAMAGING WIND GUSTS. THE
RISK WILL BE HIGHEST WEST OF A ROUGHLY JACKSONVILLE TO ALTONA LINE
WHERE EVEN A QLCS TORNADO ISN'T OUT OF THE QUESTION GIVEN (IF YOU
BELIEVE THE RAP) OVER 100 J/KG OF 0-3 CAPE AND ~30 KT OF 0-3KM LINE-
NORMAL BULK SHEAR. HOWEVER, AS THE STORMS MORE DRAMATICALLY WEAKEN
THE RISK FROM DAMAGING WINDS WILL BE A BIT MORE SPORADIC AND
CONDITIONAL ON WHETHER THE STRONGEST DOWNDRAFTS CAN PUNCH THROUGH
THE BUILDING NOCTURNAL TEMPERATURE INVERSION TO MIX THE STRONG LLJ
WINDS DOWN TO THE SURFACE.
THAT BEING SAID, THERE IS ONE CELL IN CENTRAL/NORTHEAST MO THAT IS
CURRENTLY LIFTING NORTH-NORTHEAST TOWARDS THE FAR WESTERN PORTION OF
THE ILX CWA. IF IT STAYS ON ITS CURRENT TRAJECTORY, IT MAY CLIP
WESTERN SCHUYLER COUNTY IN JUST A COUPLE HOURS...BUT IT WILL BE
CLOSE. WE'LL KEEP AN EYE ON THAT CELL AND ANY OTHERS THAT MAY
ATTEMPT TO FORM IN THE WARM SECTOR AHEAD OF THE MAIN LINE OF STORMS.
***** FLOODING RISK TOO? *****
AT THIS TIME YESTERDAY, A FEW OF THE CAMS SHOWED ONE OR TWO HP
SUPERCELLS FORMING AHEAD OF THE MAIN LINE ACROSS OUR WEST. THOSE
WOULD HAVE POSED A FLASH FLOODING RISK FROM >1.5"/H RAIN RATES, BUT
AT THIS TIME NONE OF THE CAMS ARE SHOWING STORMS UNTIL THE STRONGLY
FORCED LINE ARRIVES MID-LATE THIS EVENING. GIVEN THE ORIENTATION OF
SHEAR ALONG THE LINE OF STORMS, MEAN STORM MOTION WILL BE 50-60 MPH
TOWARDS THE NORTH-NORTHEAST, WHILE THE COLLECTIVE QLCS WILL BE
SLIDING TOWARDS THE EAST AROUND 30-40 MPH...WHICH COULD MAKE FOR
SOME MINOR TRAINING OF STORMS. HOWEVER, WITH THE LATER ARRIVAL TIME
OF STORMS AND HENCE WEAKER INSTABILITY OVER OUR AREA, THINKING THEY
WON'T BE PRODUCING HEAVY ENOUGH RAIN RATES TO CAUSE FLOODING; IN
FACT, WE MAY NOT HAVE A WHOLE LOT OF THUNDER AT ALL WITH THIS LINE.
NONETHELESS, THE RISK IS NONZERO ESPECIALLY IN URBAN AREAS WHERE
SURFACES ARE HYDROPHOBIC, SO WE'LL KEEP ONE EYE ON THAT AS WELL.
***** GUSTY WINDS TONIGHT INTO MONDAY *****
IT'S PROBABLY SUPERFLUOUS TO MENTION THE GUSTY WEST-SOUTHWESTERLY
GRADIENT WINDS TONIGHT INTO MONDAY AFTER SUCH A WINDY SPRING AND IN
LIGHT OF POSSIBLE CONVECTIVE GUSTS OVER 60 MPH TONIGHT, BUT JUST SO
NO ONE'S CAUGHT OFF GUARD: BUFKIT MIXING TECHNIQUE ADVERTISES
POTENTIAL FOR SOME CONTINUED SPORADIC 35-45 MPH GUSTS BEHIND THE
COLD FRONT TONIGHT INTO TOMORROW MORNING. WE'RE NOT ENTIRELY
CONVINCED MIXING WILL BE DEEPLY ENOUGH FOR THAT, BUT CERTAINLY
TOMORROW WILL BE BREEZY ESPECIALLY ALONG THE I-74 CORRIDOR - IN
CLOSER PROXIMITY TO THE DEPARTING SURFACE LOW.
***** THUNDERSTORM CHANCES RETURN MIDWEEK *****
BEHIND THE COLD FRONT, CONDITIONS WILL TURN DRIER ON MONDAY AND
SHOULD REMAIN TOO DRY TO SUPPORT MORE PRECIP UNTIL PERHAPS TUESDAY
AFTERNOON OR EVENING WHEN AN ILL-DEFINED MID LEVEL DISTURBANCE MAY
SPARK A COUPLE SHOWERS AND STORMS NORTH OF ROUGHLY A MACOMB TO
GIBSON CITY LINE. A LACK OF APPRECIABLE WIND SHEAR AND WEAK
INSTABILITY SUGGEST A LOW (LESS THAN 5%) RISK FOR ORGANIZED SEVERE
WEATHER, THOUGH THE INVERTED V TO AROUND 800-850 MB ON GFS FORECAST
SOUNDINGS SUGGESTS THERE COULD BE SOME LOCALIZED GUSTY OUTFLOWS.
THE DETERMINISTIC ECMWF SUGGESTS ANOTHER ROUND OF DIURNALLY DRIVEN,
GARDEN VARIETY THUNDERSTORMS MAY FORM AGAIN IN A WEAKLY SHEARED
ENVIRONMENT WEDNESDAY AFTERNOON-EVENING ONCE MORE ACROSS OUR
NORTHERN COUNTIES, BUT CONFIDENCE IS LOW IN THIS WAVE OF POSSIBLE
SHOWERS, WITH LREF PRECIP PROBABILITIES ONLY AROUND 20-30%.
PRECIP CHANCES INCREASE THURSDAY INTO FRIDAY AS A MORE PRONOUNCED
WAVE FEATURING AN ATTENDANT SURFACE LOW AND COLD FRONT LIFTS THROUGH
THE REGION. PRECISE TIMING REMAINS UNCLEAR, BUT HIGHEST PRECIP
CHANCES ARE CURRENTLY FORECAST FOR FRIDAY AT 50-70%. A THIS TIME,
GLOBAL MODELS ARE EACH CONSISTENTLY ADVERTISING AN ILL-DEFINED
SURFACE LOW WHICH SUGGESTS ANEMIC KINEMATIC FIELDS AND HENCE A LOW
SEVERE WEATHER RISK.
BUMGARDNER
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1241 PM CDT SUN APR 20 2025
AS STORMS LIFT NORTH AND OUT OF CENTRAL IL EARLY THIS AFTERNOON,
OUR MAIN FORECAST CONCERN BECOMES PESKY BKN CEILINGS BETWEEN FL020
AND FL040 WHICH STRADDLES THE MVFR FLIGHT CATEGORY. HREF SUGGESTS
PROBABILITIES DECREASE FROM SOUTH TO NORTH AS THE WARM FRONT
LIFTS NORTHWARD THROUGH THE AREA OVER THE NEXT SEVERAL HOURS.
THE NEXT CONCERN IS A LINE OF SHOWERS AND EMBEDDED THUNDERSTORMS
WHICH WILL BRING GUSTY WINDS AS IT SWEEPS WEST TO EAST ACROSS THE
TERMINALS BETWEEN ROUGHLY 01Z AND 06Z. FOR THIS A PROB30 GROUP WAS
USED TO MENTION THE THUNDER POTENTIAL, AS WELL AS ERRATIC WIND
GUSTS TO 40-45 KT. AHEAD OF THOSE STORMS, A SHORT PERIOD OF LLWS
IS EXPECTED AS A STRENGTHENING LLJ INCREASES EAST-SOUTHEAST WINDS
TO 50 KT AROUND FL020.
BEHIND THAT LINE OF STORMS AND THEIR ASSOCIATED COLD FRONT, A DRY
SLOT MAY BRING A BRIEF END TO THE LOW CLOUDS, BUT GUIDANCE
ADVERTISES HIGH CONFIDENCE (70%+ CHANCE) IN MVFR OR LOWER CEILINGS
AS WRAP AROUND MOISTURE ENTERS THE PICTURE A FEW HOURS LATER. IN
ADDITION, WINDS BEHIND THE FRONT WILL SWITCH AROUND TO
SOUTHWESTERLY AND MAY CONTINUE TO GUST OVER 25 KT THROUGH THE
NIGHT AND INTO MONDAY MORNING.
BUMGARDNER
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
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