108
FXUS63 KILX 181840
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
140 PM CDT SUN MAY 18 2025
KEY MESSAGES
- A BACK DOOR COLD FRONT WILL MOVE IN LATE THIS EVENING. THIS WILL
RESULT IN A SHIFT TO BREEZY EAST-NORTHEASTERLY WINDS (GUSTS
20-25 MPH) BETWEEN 10 PM AND 1 AM.
- AN UNSETTLED PATTERN WILL RESULT IN SEVERAL CHANCES FOR SHOWERS
AND STORMS FROM EARLY MONDAY MORNING THROUGH WEDNESDAY, SOME OF
WHICH COULD BE SEVERE MONDAY AFTERNOON/NIGHT AND TUESDAY
AFTERNOON. TOTAL RAINFALL AMOUNTS COULD EXCEED 2" (30-60%
CHANCE).
DISCUSSION
ISSUED AT 134 PM CDT SUN MAY 18 2025
AT THE START OF THE PERIOD, AN UPPER TROUGH WAS EVIDENT OVER THE
INTERMOUNTAIN WEST WITH LEE CYCLOGENESIS UNDERWAY EAST OF THE
ROCKIES. THE RESULTANT SFC LOW WILL BE SLOW MOVING OVER THE COMING
DAYS, AND AS IT BEGINS TO INFLUENCE OUR WEATHER LOCALLY IT WILL
RESULT IN SEVERAL ROUNDS OF SHOWERS/STORMS, SOME OF WHICH COULD
BE SEVERE OR PRODUCE HEAVY RAINFALL. AS NOTED YESTERDAY, THE
POTENTIAL SEVERE HAZARDS WILL BE DRIVEN IN LARGE PART BY THE
LOCATION OF A WARM FRONT.
*** TONIGHT ***
FOR TONIGHT, GUIDANCE HAS CONSISTENTLY SHOWN A BACKDOOR COLD
FRONT/SYNOPTICALLY ENHANCED LAKE BREEZE PUSHING IN FROM NE IL THIS
EVENING. THE MOST NOTICEABLE IMPACT OF THIS FEATURE WILL BE A
SHIFT TO BREEZY ENE WINDS (GUSTS TO 25 MPH) REACHING THE I-74
CORRIDOR AROUND 10 PM, THEN LOCATIONS TO THE SOUTH IN THE
SUBSEQUENT HOURS. THE LESS NOTICEABLE IMPACT OF THIS FEATURE IS
THE ROLE IT COULD PLAY IN KEEPING THE WARM FRONT WELL SOUTH OF THE
ILX CWA TONIGHT. STORMS ARE LIKELY TO FIRE ACROSS THE CENTRAL
PLAINS THIS AFTERNOON, WITH ADDITIONAL DEVELOPMENT ACROSS E KS/MO
DURING THE LATE EVENING AS LLJ FORCING RAMPS UP. THIS DEVELOPMENT
COULD PROVIDE A ROUND OF PRECIP TO THE ILX CWA OVERNIGHT INTO
EARLY MON AM, ALTHOUGH IT'S WORTH NOTING THAT MOST GUIDANCE HAS
SHIFTED THE TRACK OF THIS WEAKENING CONVECTIVE COMPLEX SOUTHWARD
COMPARED TO PREVIOUS FORECASTS. IT DOES SEEM LIKE WHATEVER
CONVECTIVE COMPLEX MOVES OUR WAY OVERNIGHT WILL BE ENCOUNTERING
SOME DRY AIR, AS AMBIENT PWAT VALUES ARE JUST 0.50- 0.75". PRECIP
CHANCES DURING THIS PERIOD WILL BE HIGHER WITH SOUTH EXTENT, WITH
THE LATEST FORECAST INDICATING A 50-60% CHANCE SOUTH OF I-72 AND A
40-50% CHANCE TO THE NORTH, THOUGH IT'S WORTH NOTING THAT BOTH OF
THOSE ARE LOWER THAN PREVIOUS FORECASTS AND THE POPS MAY NEED TO
BE LOWERED FURTHER IF THE LATEST CAM TRENDS HOLD. MOST MODELS SHOW
LITTLE IN THE WAY OF ELEVATED INSTABILITY ACROSS OUR AREA
TONIGHT. THE ONE EXCEPTION IS THE NAM, ALTHOUGH THIS MODEL IS ALSO
AN OUTLIER IN TERMS OF THE PRECIP TRACK. THE THINKING IS THE
SEVERE RISK IS QUITE LOW TONIGHT DUE TO THE LIMITED INSTABILITY.
*** MONDAY - MONDAY NIGHT ***
INTO THE DAY ON MON, THE SFC LOW IS FORECAST TO BE POSITIONED OVER
THE CNTRL PLAINS, WITH THE WARM FRONT EXTENDING SE TOWARDS ST.
LOUIS, MO. WHILE SOME SCATTERED SHOWERS/SHOWERS CAN'T BE RULED
OUT DURING THE LATE MORNING/AFTERNOON MON (AFTER THE INITIAL
EARLY MORNING WAVE IS GONE), THE THINKING IS THAT COVERAGE WILL BE
QUITE LIMITED OWING IN PART TO SUBSIDENCE/LIMITED FORCING IN THE
WAKE OF THE MORNING WAVE. MODELS SHOW MARGINAL ELEVATED
INSTABILITY PRESENT, SO IF STORMS DO FORM THEY COULD PERHAPS POSE
A SMALL HAIL THREAT, BUT WITH THE SFC FRONT STILL FIRMLY SOUTH OF
THE AREA SFC-BASED STORMS ARE NOT EXPECTED.
SCATTERED CONVECTIVE DEVELOPMENT APPEARS LIKELY ACROSS THE EASTERN
PLAINS MON AFTERNOON INTO THE EVENING, WITH COVERAGE INCREASING
FURTHER AS UPSCALE GROWTH AND LLJ FORCING RETURN. THESE WIDESPREAD
SHOWER AND STORMS WILL PUSH INTO THE ILX CWA FROM THE WEST LATE
MON EVE INTO THE OVERNIGHT HOURS (>90% CHANCE OF RAIN). MODELS
DEPICT THE WARM FRONT ADVECTING NORTHWARD DURING THIS TIME FRAME,
THOUGH HOW FAR NORTH WILL REMAIN A POINT OF UNCERTAINTY UNTIL WE
HAVE A BETTER HANDLE ON HOW THE PREVIOUS ROUNDS OF CONVECTION
UNFOLD. SOUTHERN COUNTIES OF ILX CWA HAVE THE BEST CHANCE OF BEING
NEAR THE FRONT, WHERE THERE COULD BE A NARROW CORRIDOR SUPPORTIVE
OF SFC- BASED SEVERE STORMS CAPABLE OF ALL HAZARDS. DEEP LAYER
SHEAR VECTORS ARE ORIENTED ALMOST PERPENDICULAR TO THIS FRONTAL
ZONE, HOWEVER, SUGGESTING VERY BRIEF RESIDENCE TIME FOR ANY
INDIVIDUAL STORMS TO BECOME SFC-BASED. NORTH OF THE FRONT,
INSTABILITY PROGS ARE VARIABLE, BUT THERE COULD BE SUFFICIENT
INSTABILITY TO SUPPORT SEVERE HAIL (MUCAPES UP TO 1500 J/KG IN THE
SW PORTIONS OF THE CWA, DECREASING TO THE NORTH).
THE METEOROLOGICAL FACTORS FOR HEAVY RAINFALL NOTED IN PREVIOUS
DISCUSSIONS LARGELY REMAIN ON TRACK: ANOMALOUS PWAT VALUES OVER
1.5", DEEP WARM CLOUD LAYER (>10 KFT), AND RELATIVELY SKINNY CAPE
PROFILES (AROUND 1000 J/KG OR LESS) WILL ALL SUPPORT HIGH RAINFALL
RATES, BUT STRONG WIND FIELDS WILL KEEP INDIVIDUAL CELLS
PROGRESSIVE. STILL, THE SOUTHERLY LLJ WILL BE DRIVING AIR
CONTAINING RICH MOISTURE TO OVERRUN THE WARM FRONT. CAMS DEPICT A
FAIRLY LARGE SWATH OF 1.5-3" OF RAINFALL MON NIGHT (NORTH OF I-70
AND EAST OF IL RIVER). 6-HR FLASH FLOOD GUIDANCE VALUES CURRENTLY
RANGE FROM 2.25 - 4" ACROSS THESE AREAS. THOSE VALUES COULD
DIMINISH IF WE DO SEE APPRECIABLE RAINFALL LATE SUN NIGHT-EARLY
MON AM, WHICH WOULD INCREASE THE FF POTENTIAL, HOWEVER, AS NOTED
ABOVE PRECIP CHANCES ARE ON A DOWNWARD TREND FOR THE LATE SUN-
EARLY MON TIME PERIOD.
*** TUESDAY - TUESDAY NIGHT ***
NOTED YESTERDAY THAT TUES APPEARED TO HAVE THE BEST POTENTIAL FOR
SEVERE STORMS IN THE ILX CWA. WHILE TUES STILL APPEARS TO BE THE
DAY WHERE WE ARE MOST LIKELY TO SEE THE WARM FRONT LIFT NORTH INTO
OUR AREA, THE WIDESPREAD PRECIP MON NIGHT INTO TUES AM NOW LEAVE
QUESTIONS ABOUT WHETHER SUFFICIENT ATMOSPHERIC RECOVERY WILL OCCUR
BEFORE THE WARM SECTOR SHIFT EAST OF THE AREA. WILL STILL NEED TO
MONITOR THE SEVERE STORM POTENTIAL, BUT THE INSTABILITY PROGS DID
TREND QUITE A BIT LOWER COMPARED TO PREVIOUS CYCLES. IF SEVERE
STORMS WERE TO OCCUR, GUIDANCE STILL SUGGESTS THE THREAT WOULD
PRIMARILY BE NEAR AND SOUTH/EAST OF I-72/DANVILLE DURING TUES
AFTERNOON.
*** REST OF THE WEEK ***
THE SFC LOW WILL STEADILY SHIFT EAST INTO WED, REACHING PA BY WED
MORNING. IL WILL REMAIN IN THE CYCLONIC FLOW REGIME, WITH BREEZY
NW WINDS ACTING TO USHER IN A COOLER AIR MASS (850 MB TEMPS IN THE
LOW SINGLE DIGITS DEGC). THE RESULT WILL BE A SEASONABLY COOL
TODAY, WITH HIGHS STRUGGLING TO REACH THE 60S. SOME LINGERING
LIGHT PRECIP IS POSSIBLE (20-30% CHANCE), MAINLY NEAR/NORTH OF THE
I-74 CORRIDOR. TEMPS REMAIN ON THE COOL SIDE THROUGH THE LATTER
HALF OF THE WORK WEEK, ALTHOUGH THEY GRADUALLY WARM EACH DAY.
MOSTLY DRY CONDITIONS SHOULD PREVAIL THURS-FRI AS WEAK SFC HIGH
PRESSURE APPROACHES THE REGION.
ERWIN
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1251 PM CDT SUN MAY 18 2025
VFR CONDITIONS WILL PREVAIL AT ALL TAF SITES NEXT 24HRS. CLEAR
SKIES OR WHICH CIRRUS WILL COVER EACH SITE UNTIL LATE TONIGHT. A
FRONTAL SYSTEM WILL BRING SHOWERS TO WESTER CENTRAL ILLINOIS LATE
TONIGHT THROUGH EARLY MORNING. ALL SITES WILL HAVE PROB30 FOR
SHOWERS WITH CIGS LOWERING TO MID LEVELS, THEN LOWER WITH THE
TEMPO GROUP. SPI AND DEC WILL SEE PREDOMINATE SHOWERS IN THE
MORNING HOURS. WINDS WILL BE LIGHT OUT OF THE NORTHWEST AS A HIGH
PRESSURE RIDGE MOVES ACROSS THE SITES THIS EVENING. EASTERN WINDS
ARRIVE THIS EVENING INTO THE OVERNIGHT HOURS AND TOMORROW, WITH
HIGHEST WIND SPEEDS OF 20-22KTS AT ALL SITES.
AUTEN
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
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