643
FXUS63 KILX 260745
AFDILX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LINCOLN IL
245 AM CDT SAT APR 26 2025
KEY MESSAGES
- THERE IS A SLIGHT (15-30%) CHANCE FOR PATCHY FROST IN RURAL
AREAS EAST OF A ROUGHLY PEORIA TO TERRE HAUTE LINE TONIGHT.
THIS COULD DAMAGE NEWLY EMERGED TENDER VEGETATION IF IT IS LEFT
UNCOVERED.
- GUSTY SOUTHERLY WINDS MAY MAKE FOR DIFFICULT TRAVEL FOR HIGH
PROFILE VEHICLES MONDAY AFTERNOON AND EVENING. 30-35 MPH WIND
GUSTS WILL BE MOST COMMON, BUT THERE IS A 30-50% FOR A SPORADIC
GUST OR TWO TO SURPASS 40 MPH.
- THERE IS A 15% CHANCE FOR SEVERE WEATHER MONDAY NIGHT WEST OF A
LITCHFIELD TO HOOPESTON LINE, AND EAST OF THE IL RIVER ON
TUESDAY. THIS CORRESPONDS TO A LEVEL 2 OF 5 (SLIGHT) RISK.
DISCUSSION
ISSUED AT 231 AM CDT SAT APR 26 2025
***** SEASONABLY COOL THROUGH THE WEEKEND *****
MID LEVEL WATER VAPOR SATELLITE SHOWS AN UPPER TROUGH DRIFTING EAST-
SOUTHEAST FROM THE UPPER MIDWEST INTO THE GREAT LAKES, WHILE BROAD
ZONAL FLOW ALOFT PREVAILS FURTHER SOUTH. AT THE SURFACE, 10-15 MPH
NORTHERLY WINDS CONTINUE TO ADVECT A COOLER AND DRIER AIRMASS INTO
CENTRAL IL, WITH TEMPERATURES ALONG THE I-74 CORRIDOR DROPPING INTO
THE UPPER 40S TO LOW 50S AT 2AM. THESE WINDS WILL VEER GRADUALLY TO
A MORE EASTERLY DIRECTION AND EASE TODAY AS SURFACE HIGH PRESSURE
BUILDS INTO THE GREAT LAKES BEHIND THE AFOREMENTIONED UPPER TROUGH.
SUBSIDENCE ASSOCIATED WITH A RIDGE BUILDING INTO THE REGION WILL
RESULT IN A SUNNY AFTERNOON, THOUGH IT WILL BE COOLER COMPARED TO
THE PAST SEVERAL DAYS WITH HIGHS IN THE MID 60S. WHILE TOMORROW
AFTERNOON WILL BE GENERALLY 3-5 DEGF WARMER AS THE RIDGE AMPLIFIES
OVER THE MIDWEST, THE MORNING WILL BE QUITE CHILLY GIVEN THE DRY
AIRMASS AND LIGHT-CALM WINDS. A FEW MID TO HIGH CLOUDS MAY OFFSET
RADIATIONAL COOLING ESPECIALLY ACROSS THE SOUTHWEST CWA, BUT NBM
GIVES A 15-30% CHANCE FOR LOW TEMPERATURES LESS THAN 37 DEGF EAST OF
A ROUGHLY PEORIA TO TERRE HAUTE LINE; THIS IS APPROXIMATELY THE 2M
TEMPERATURE NEEDED FOR FROST FORMATION UNDER CONDITIONS FAVORABLE
FOR EFFICIENT RADIATIONAL COOLING.
***** BREEZY AND WARM MONDAY *****
SUNDAY NIGHT INTO MONDAY, AN UPPER TROUGH WILL LIFT OUT OF THE GREAT
BASIN AND INTO THE NORTHERN PLAINS. THE APPROACH OF A DEVELOPING LEE
CYCLONE TRACKING INTO THE UPPER MIDWEST WILL TIGHTEN THE SURFACE
PRESSURE GRADIENT ACROSS THE AREA ON MONDAY AS HIGH PRESSURE SLOWLY
SHIFTS EAST. SOUTHERLY WINDS WILL THUS INCREASE WITH GUSTS OVER 30
MPH COMMON DURING THE AFTERNOON AND EVENING. A 50-60 KT LLJ
INTENSIFIES OVER THE CWA MONDAY EVENING, THOUGH FORECAST SOUNDINGS
SUGGEST A CAPPING INVERSION WILL SHIELD THE SURFACE FROM THE
STRONGEST WINDS ALOFT OUTSIDE OF CONVECTION. NONETHELESS, IF
MIXING IS AS DEEP AS THE GFS AND NAM SUGGEST, BUFKIT MIXING
TECHNIQUES WOULD SUGGEST SOME SPORADIC GUSTS TO 40+ MPH MAY OCCUR;
THIS IS ALSO SUPPORTED BY CALIBRATED ENSEMBLE GUIDANCE, WITH NBM
GIVING A 30-60% CHANCE (HIGHEST WEST) FOR PEAK GUSTS EXCEEDING 40
MPH WEST OF ROUGHLY I-57 MONDAY AFTERNOON-EVENING. COMBINING THESE
GUSTY WINDS WITH SOIL MOISTURE RUNNING A 10-30% DEFICIT NORTH OF
ROUGHLY I-72 (2 IN SOIL MOISTURE AT SPI, FOR EXAMPLE, IS
SEASONABLY LOW AT AROUND 0.33 WFV) COULD RESULT IN BLOWING DUST
WITH SPRING PLOWING, PARTICULARLY IF WINDS WIND UP VERIFYING ON
THE HIGHER END OF GUIDANCE, BUT THIS REMAINS A LOW CONFIDENCE
FORECAST CONCERN AT THIS TIME. TEMPERATURES IN THIS STRONG WARM
AIR ADVECTION (WAA) REGIME WILL SOAR INTO THE 80S AREA-WIDE, AND
IF WE WIND UP WITH ENOUGH SUNSHINE WE WOULDN'T BE SURPRISED TO SEE
AFTERNOON TEMPERATURES CLOSER TO THE NBM 75TH PERCENTILE WHICH IS
IN THE MID 80S.
***** SEVERE WEATHER RISK LATE MONDAY INTO TUESDAY *****
THE MOST SIGNIFICANT WEATHER CONCERN REMAINS THE PROSPECT OF SEVERE
WEATHER MONDAY NIGHT AND AGAIN TUESDAY. THINKING IS STILL THAT
DURING THE DAY MONDAY THE CAPPING INVERSION AROUND 700-800MB AND
LACK OF A TRIGGER WILL KEEP US DRY. HOWEVER, THE SUBSTANTIAL
INSTABILITY (LREF MEAN IS 1500-2300 J/KG) ABOVE THAT CAP, TOGETHER
WITH 45-60 KT OF 0-6KM BULK SHEAR, IS MORE THAN ENOUGH TO SUSTAIN
STORMS ONCE THEY GET GOING. FORTUNATELY, STORMS ARE SLATED TO
DEVELOP ALONG THE COLD FRONT WELL UPSTREAM DURING THE DAY MONDAY,
AND BY THE TIME THEY REACH US WE MAY (EMPHASIS ON "MAY") BE
DECOUPLED AT THE SURFACE; THIS WOULD LIMIT THE RISK FOR TORNADOES
AND DAMAGING WINDS. HOWEVER, IF STORMS CONGEAL INTO A LINE OR LINEAR
CLUSTERS, WE MAY STILL WIND UP WITH SOME DAMAGING GUSTS AND MAINTAIN
A RISK FOR QLCS TORNADOS GIVEN THE ORIENTATION OF 0-3KM SHEAR WHICH
IS GENERALLY IN THE SAME DIRECTION AS STORM MOVEMENT (WEST TO EAST),
OR ROUGHLY PERPENDICULAR TO ANY LINEAR SEGMENTS ("LINE NORMAL"). THE
HIGHEST RISK MONDAY NIGHT REMAINS ACROSS OUR WESTERN COUNTIES WHERE
(1) KINEMATIC PARAMETERS ARE STRONGER AND (2) STORMS STAND A BETTER
CHANCE OF ARRIVING BEFORE THE SURFACE BECOMES DECOUPLED AND
INSTABILITY NOCTURNALLY WANES.
THE POSITION OF THE SURFACE COLD FRONT WILL BE CRUCIAL TO
IDENTIFYING WHERE THE SEVERE RISK IS MAXIMIZED ON TUESDAY, AS AREAS
NORTHWEST OF THE BOUNDARY WILL BE IN THE CLEAR WHILE ALONG AND EAST
OF IT SCATTERED TO NUMEROUS THUNDERSTORMS DEVELOPING DURING THE
AFTERNOON MAY QUICKLY TURN SEVERE. KINEMATIC PARAMETER FIELDS ARE
NOT QUITE AS STRONG ON TUESDAY, AND BULK SHEAR VECTORS BECOME
ORIENTED MORE PARALLEL TO THE BOUNDARY FAVORING A LINEAR STORM MODE
WITH A LOW (THOUGH STILL NOT ZERO) RISK FOR TORNADOES. HOWEVER, THE
2000-3000 J/KG OF MUCAPE ADVERTISED BY THE DETERMINISTIC ECMWF
AND GFS SUGGEST PLENTIFUL INSTABILITY TO SUSTAIN STORMS ALONG THE
FRONT. IN ADDITION, THE MORE FAVORABLE DIURNAL TIMING OF STORMS
WOULD SUGGEST A NOTABLE RISK FOR DAMAGING WIND GUSTS AT THE
SURFACE, ESPECIALLY CONSIDERING PWATS CLIMBING TO OVER 1.5 INCHES
(FAVORS PRECIP LOADING OF DOWNDRAFTS), MID LEVEL DRY AIR APPARENT
ON FORECAST SOUNDINGS, AND STEEP LOW LEVEL LAPSE RATES. NOW, WHERE
PRECISELY THAT COLD FRONT IS SITUATED TUESDAY AFTERNOON IS THE
QUESTION ANSWERED DIFFERENTLY BY INDIVIDUAL MODELS AND THEIR
RESPECTIVE ENSEMBLES. FOR EXAMPLE, THE GFS HOLDS IT NEAR I-72,
WHILE THE ECMWF STALLS THE BOUNDARY CLOSER TO I-70. WE'LL CONTINUE
TO MONITOR AND MENTION NEW INFORMATION AS WE SEE IT.
***** REST OF THE WORK WEEK *****
IT LOOKS INCREASINGLY LIKELY THAT ANOTHER SYSTEM WILL PUSH THAT
BOUNDARY BACK NORTH AND PROVIDE ADDITIONAL RAIN CHANCES SOMETIME
LATER IN THE WEEK, THOUGH INDIVIDUAL MODELS VARY ON PRECISELY WHEN.
TEMPERATURES WILL TREND NEAR TO SLIGHTLY BELOW NORMAL WEDNESDAY AND
THURSDAY GIVEN THE LREF MEAN HOLDS THAT FRONT NEAR/SOUTH OF CENTRAL
IL, BUT A TIGHT GRADIENT IN TEMPERATURES (AND PRECIPITATION CHANCES)
IS EXPECTED TO EVENTUALLY COME INTO THE FORECAST AS IT BECOMES
APPARENT WHERE THAT FRONT WILL SET UP - TEMPERATURES RUNNING MUCH
WARMER (COOLER) SOUTH (NORTH) OF THE BOUNDARY.
BUMGARDNER
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1210 AM CDT SAT APR 26 2025
PATCHY LOW STRATUS IS IN PLACE OVER A GOOD PORTION OF CENTRAL
ILLINOIS LATE TONIGHT, RESULTING IN MVFR CEILINGS AT MOST
AIRFIELDS. SOME HOLES IN THE STRATUS COULD ALLOW SITES TO BRIEFLY BOUNCE
TO VFR AT TIMES, BUT CEILINGS SHOULD PREDOMINATELY BE MVFR
OVERNIGHT. CLOUDS SHOULD CLEAR BY MID TO LATE MORNING AS STRONG
SURFACE HIGH PRESSURE MOVES INTO THE WESTERN GREAT LAKES REGION.
NORTH-NORTHEAST WINDS WILL VEER TO THE EAST BY SATURDAY EVENING
WITH SPEEDS LOOKING TO GENERALLY REMAIN BELOW 15 KTS.
NMA
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
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