498
FXUS63 KILX 172323
AFDILX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE LINCOLN IL
623 PM CDT SAT MAY 17 2025
KEY MESSAGES
- UNSETTLED WEATHER RETURNS LATE SUNDAY NIGHT THROUGH WEDNESDAY,
WITH SEVERAL ROUNDS OF SHOWERS AND STORMS EXPECTED DURING THAT
PERIOD. SOME OF THE STORMS COULD BE SEVERE ON MONDAY AND
TUESDAY, AND LOCALLY HEAVY RAINFALL IN EXCESS OF 2" IS ALSO
POSSIBLE (30-50% CHANCE).
DISCUSSION
ISSUED AT 231 PM CDT SAT MAY 17 2025
AN UPPER LOW WAS EVIDENT IN SATELLITE IMAGERY NORTHEAST OF THE
GREAT LAKES. CENTRAL IL REMAINS IN THE CYCLONIC FLOW REGIME
ASSOCIATED WITH THIS LOW PRESSURE SYSTEM, WITH BREEZY WESTERLY
WINDS GUSTING UP TO 35 MPH. THESE GUSTS ARE RIGHT AROUND THE
THRESHOLD AT WHICH WE SEE BLOWING DUST DEVELOP, AND WE RECEIVED
REPORTS OF LOCALIZED BLOWING DUST REDUCING VIS ALONG I-74 BETWEEN
BLOOMINGTON AND CHAMPAIGN BETWEEN NOON AND 130PM. NO OTHER REPORTS
HAVE BEEN RECEIVED AS OF THIS WRITING. A BLOWING DUST ADVISORY
WAS ISSUED FOR MOST AREAS EAST OF THE IL RIVER AND NORTH OF I-70.
THE COUNTIES INCLUDED IN THE ADVISORY WERE BASED ON THE COUNTIES
WHERE TILE DRAINAGE IS MOST PREVALENT, WHICH OUR LOCAL RESEARCH
HAS IDENTIFIED AS BEING A FACTOR THAT CAN INCREASE THE BLOWING
DUST POTENTIAL. WIND GUSTS SHOULD DIMINISH INTO THIS EVENING (AND
THUS THE THREAT OF BLOWING DUST WILL AS WELL).
THE REMAINDER OF THE WEEKEND SHOULD BE PLEASANT ACROSS THE REGION
AS A WEAK SFC HIGH PRESSURE SHIFTS THROUGH, RESULTING IN LIGHT
WINDS AND MOSTLY CLEAR SKIES ON SUN. TEMPS TONIGHT WILL BE ON THE
COOL SIDE, WITH LOWS RANGING FROM THE MID 40S IN THE NORTH TO MID
50S IN THE SOUTH. TYPICAL LOWS FOR THIS TIME OF YEAR ARE IN THE
LOW/MID 50S. HIGHS SHOULD BE SEASONABLE ON SUNDAY, IN THE MID 70S.
LATE SUN EVE, CAMS SUGGEST A BACK DOOR COLD FRONT EMANATING FROM
NE IL PUSHING SOUTHWEST ACROSS THE ILX CWA. CURRENT TIMING
SUGGESTS THIS OCCURS BETWEEN 9PM SUN AND 1AM MON, BUT THAT COULD
BE ADJUSTED SLIGHTLY IN SUBSEQUENT FORECASTS. THE MAIN IMPACT WITH
THIS FRONT WOULD BE A SHIFT FROM LIGHT WINDS TO NORTHEASTERLY
WINDS THAT COULD GUST 20-25 MPH.
*** MONDAY - TUESDAY SEVERE STORM POTENTIAL ***
ATTENTION THEN TURNS TO A SLOW-MOVING, LONG WAVE TROUGH THAT IS
SET TO EMERGE ONTO THE CENTRAL PLAINS SUN-MON. THIS SYSTEM WILL
RESULT IN AN UNSETTLED PATTERN LOCALLY, WITH MULTIPLE ROUNDS OF
STORMS POSSIBLE MON-TUES INCLUDING A CHANCE FOR BOTH SEVERE STORMS
AND LOCALLY HEAVY RAINFALL. THE SEVERE STORM HAZARDS WILL BE
MODULATED IN LARGE PART BY THE POSITION OF A WARM FRONT.
THE FIRST CHANCE FOR PRECIP IS DURING THE PRE-DAWN HOURS OF MON
AM. AT THIS TIME, THE WARM FRONT IS LIKELY TO BE POSITIONED SOUTH
OF THE ILX CWA. BETWEEN UPSCALE GROWTH OF CONVECTION ACROSS THE
PLAINS AS WELL AS LLJ FORCING INTO THE WARM FRONT, MOST MODELS
BRING PRECIP INTO THE ILX CWA BY 2-3 AM MON. THERE IS A BROAD
SPREAD IN THE MODELS IN TERMS OF HOW MUCH ELEVATED INSTABILITY IS
PRESENT AT THAT TIME, RANGING FROM LESS THAN 1000 J/KG TO UPWARDS
OF 2000 J/KG DEPENDING ON THE GUIDANCE SOURCE, BUT GIVEN THE
SYNOPTIC PLACEMENT OF THIS PRECIP THE THINKING IS IF A SEVERE
THREAT EXISTS IT WOULD PRIMARILY BE FOR HAIL. THERE MAY ALSO BE A
MARGINAL THREAT FOR STRONG WIND GUSTS DEPENDING ON HOW ORGANIZED
THE INCOMING CONVECTION IS. EFF INFLOW LAYER SHEAR OF 50+ KNOTS
COULD BE SUFFICIENT FOR THESE STORMS TO MAINTAIN AN ORGANIZED
STRUCTURE CAPABLE OF THOSE STRONGER WIND GUSTS. THE MAIN TAKEAWAY
IS TO EXPECT SCATTERED SHOWERS AND STORMS VERY EARLY MONDAY
MORNING, WITH THE HIGHEST CHANCES ACROSS THE SOUTHERN HALF OF THE
ILX CWA.
AS WE PROGRESS THROUGH THIS EVENT, THE REPEATED ROUNDS OF
CONVECTION LEAVE UNCERTAINTY AS TO WHERE THE WARM FRONT WILL BE
POSITIONED. THERE IS GOOD CONSISTENCY IN THE STORM EVOLUTION EARLY
MON AM, AND I SUSPECT THOSE STORMS COULD REINFORCE THE WARM FRONT
FURTHER TO THE SOUTH. THUS I LEAN MORE TOWARDS THE 17.12Z
DETERMINISTIC NAM SOLUTION WHICH HAS THE WARM FRONT FURTHER SOUTH
(SOUTH OF THE ILX CWA DURING THE DAY MON) COMPARED TO THE GFS
SOLUTION. GUIDANCE HAS A RELATIVE LULL IN PRECIP ACTIVITY DURING
THE DAY MON, BEFORE BECOMING MORE WIDESPREAD INTO THE EVENING AS
THE LLJ FORCING RETURNS. WHILE PRECIP COVERAGE IS LESS CERTAIN
DURING THE DAY MON, GUIDANCE SHOWS A PLUME OF STEEP MID-LEVEL
LAPSE RATES ADVECTING INTO THE AREA, INCREASING THE POTENTIAL FOR
LARGE HAIL WITH ANY STORMS THAT DO FORM. IF WE ARE CORRECT IN
FAVORING THE SOUTHERN SOLUTION FOR THE WARM FRONT PLACEMENT, HAIL
WOULD CONTINUE TO BE THE PRIMARY HAZARD INTO MON NIGHT. WILL NOTE
THAT THE FRONTAL PLACEMENT WILL STILL NEED TO BE MONITORED CLOSELY
AS THE ENVIRONMENT APPEARS QUITE FAVORABLE FOR TORNADOES ACROSS
THE WARM SECTOR MON NIGHT. THE PRECIP TIMING TRENDS OUTLINED ABOVE
SEEM TO BE WELL REFLECTED IN THE LATEST NBM POPS: 60-80% CHANCE
MON AM, 20-50% CHANCE MON AFTERNOON, THEN A GREATER THAN 90%
CHANCE INTO MON NIGHT.
ON TUES, THE SFC LOW IS EXPECTED TO TRACK ACROSS THE ILX CWA. THIS
WOULD BRING THE WARM FRONT FURTHER NORTH, AND PROVIDE A WINDOW
WHERE PORTIONS OF THE ILX CWA ARE IN THE WARM SECTOR (BEST CHANCE
BEING EAST OF I-55/SOUTH OF I-74). WITHIN THIS AREA, A VOLATILE
ENVIRONMENT WITH STRONG INSTABILITY (POTENTIALLY OVER 3000 J/KG OF
MUCAPE), STRONG DEEP LAYER SHEAR OVER 50 KNOTS, TWO FRONTS (WARM
FRONT AND COLD FRONT) AND A TRIPLE POINT COULD SUPPORT SEVERE
STORMS CAPABLE OF ALL HAZARDS ACROSS EAST-CENTRAL IL TUES
AFTERNOON, ASSUMING SUFFICIENT ATMOSPHERIC RECOVERY OCCURS AFTER
ANY EARLIER STORMS. THE PLACEMENT OF THE SPC DAY 4 SEVERE
THUNDERSTORM OUTLOOK STILL LOOKS WELL ALIGNED WITH TODAY'S 12Z
MODEL GUIDANCE, BUT PROBABILITIES MAY INCREASE IN LATER OUTLOOKS
IF CURRENT GUIDANCE HOLDS.
*** MONDAY - TUESDAY HEAVY RAIN POTENTIAL ***
THE OTHER CONCERN WITH THIS SYSTEM IS THE POTENTIAL FOR LOCALLY
HEAVY RAINFALL. GUIDANCE DEPICTS PWAT VALUES BETWEEN 1.25-1.75",
WHICH IS AROUND THE 95TH PERCENTILE OF CLIMATOLOGY. FORECAST
SOUNDINGS FROM THE NAM SUGGEST A WARM CLOUD LAYER DEPTH (CLOUD
BASE TO FREEZING LEVEL) OF 10-12 KFT FOR MUCH OF THE PERIOD FROM
EARLY MON AM THROUGH TUES AM. WARM CLOUD LAYER VALUES ABOVE 10KFT
SUGGEST EFFICIENT RAINFALL RATES. THE ONE LIMITING FACTOR COULD BE
THE KINEMATICS (SEE THE HIGH DEEP LAYER SHEAR VALUES REFERENCED
ABOVE). THE RESIDENCE TIME OF ANY INDIVIDUAL CELL WILL NOT BE TOO
LONG AT ANY ONE LOCATION, SO IT WOULD TAKE MULTIPLE ROUNDS OF
STORMS OVER THE SAME AREA, OR PERHAPS TRAINING STORMS, TO DRIVE
HIGHER RAINFALL TOTALS. CURRENTLY, THE NBM HAS A 70-90% CHANCE OF
TOTAL RAINFALL EXCEEDING 1" ACROSS MOST OF THE ILX CWA, AND A
30-50% CHANCE OF 2" OF RAIN. AS CAMS START TO ENCOMPASS THE FULL
EVENT, WE'LL GET A BETTER IDEA OF WHAT KIND OF LOCALIZED, HIGHER
END RAINFALL AMOUNTS COULD OCCUR. WPC HAS ISSUED A SLIGHT RISK OF
EXCESSIVE RAINFALL FOR THE SOUTHWEST CWA ON MONDAY, WHILE THE
ENTIRE AREA IS ENCOMPASSED IN A SLIGHT RISK FOR DAY 4.
*** REST OF THE WEEK ***
AS THE SFC LOW SLIDES EAST BY WED, BREEZY NORTHERLY FLOW WILL
PERSIST ACROSS IL THROUGH THE DAY, WITH FORECAST SOUNDINGS
SUGGESTING MOSTLY CLOUDY SKIES AND PERHAPS SOME LIGHT SHOWERS.
TEMPS WILL BE SEASONABLY COOL, WITH HIGHS BARELY CLIMBING INTO THE
LOW 60S.
THE REST OF THE WEEK FEATURES A WEAK, BROAD SFC HIGH NUDGING INTO
THE REGION, WHICH SHOULD RESULT IN GRADUALLY WEAKENING WIND SPEEDS
AND MOSTLY DRY CONDITIONS DURING THE DAY THURSDAY-FRIDAY (LESS
THAN 20% CHANCE PRECIP).
ERWIN
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 623 PM CDT SAT MAY 17 2025
VFR CONDITIONS WILL PREVAIL THROUGH THE ENTIRE 00Z TAF PERIOD. SCT
DIURNAL CU AT AROUND 6000FT WILL DRIFT OVER THE I-72 TERMINALS
OVER THE NEXT HOUR OR TWO BEFORE DISSIPATING AFTER SUNSET.
WESTERLY WINDS WILL CONTINUE TO GUST TO AROUND 20KT AT ALL SITES
THROUGH ABOUT 01Z/02Z, THEN WILL BECOME W/NW AND DECREASE TO LESS
THAN 10KT. WINDS WILL VEER TO N AT AROUND 10KT ON SATURDAY UNDER
A MOSTLY CLEAR SKY.
BARNES
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
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