957
FXUS63 KILX 270638
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
138 AM CDT MON APR 27 2026
KEY MESSAGES
- MULTIPLE ROUNDS OF THUNDERSTORMS ARE EXPECTED TODAY. THERE IS
AN ENHANCED RISK (LEVEL 3 OF 5) OF SEVERE STORMS, WITH THE
MAIN CONCERN BEING DURING THE AFTERNOON AND EVENING. STORMS
WILL BE CAPABLE OF PRODUCING TORNADOES, DAMAGING WINDS, LARGE
HAIL, AND FLASH FLOODING.
- WINDY CONDITIONS ARE EXPECTED TODAY, WITH SOUTHERLY GUSTS OF
30-40 MPH. THIS COULD LEAD TO BLOWING DUST IN AREAS THAT DO
NOT RECEIVE RAINFALL THIS MORNING.
- MORE SHOWERS AND STORMS ARE LIKELY TUESDAY EVENING, WITH THE
BEST CHANCE BEING SOUTH OF I-70 (80-90%). SEVERE STORMS ARE
NOT EXPECTED.
DISCUSSION
ISSUED AT 130 AM CDT MON APR 27 2026
*** TODAY ***
THE FOCUS REMAINS ON TODAY'S FORECAST, A CHALLENGING ONE
INVOLVING MULTIPLE ROUNDS OF CONVECTION, POTENTIAL FOR SEVERE
STORMS AND HEAVY RAINFALL, AND STRONG SYNOPTIC WINDS THAT COULD
LEAD TO BLOWING DUST. WE'VE BEEN HIGHLIGHTING THE IMPACT OF
MORNING STORMS ON TODAY'S FORECAST, WITH MORE MORNING STORMS
REDUCING THE SEVERE STORM AND BLOWING DUST CHANCES RELATIVE TO A
SCENARIO WITH FEWER MORNING STORMS. THE FORECAST HAS TRENDED
TOWARDS HIGHER STORM COVERAGE ACROSS CENTRAL IL THIS MORNING.
* MONDAY MORNING STORM CHANCES *
AT 04Z MON/11PM SUN, SFC ANALYSIS INDICATED A SUB-1000MB SFC LOW
NEAR THE OK PANHANDLE, WITH A SECONDARY SFC LOW (1004 MB) NEAR
THE WESTERN MN/IA BORDER. UPPER LEVEL FIELDS REVEAL A
NEGATIVELY-TILTED SHORTWAVE EMERGING OVER THE CENTRAL PLAINS,
EMBEDDED WITHIN A BROADER REGION OF LARGE SCALE TROUGHING OVER
THE NORTHWESTERN 1/4 OF THE CONUS. UPSTREAM OF IL, THERE WERE
TWO AREAS OF ONGOING CONVECTION AS OF 0430Z, ONE IN THE FORM OF
SCATTERED STORMS PRIMARILY SOUTH OF THE I-70 CORRIDOR IN MO AND
THE OTHER DEVELOPING NEAR THE I-70 CORRIDOR IN KS. THERE WAS
ALSO A SWATH OF LIGHT RAIN NEARING THE MS RIVER CORRIDOR,
TRACKING EAST IN TIME.
IN PREVIOUS DAYS, THE THINKING WAS THE EVOLUTION OF THE
CONVECTION ACROSS MO WAS GOING TO BE OUR PRIMARY CHANCE FOR
STORMS LOCALLY INTO THE EARLY PORTIONS OF MONDAY MORNING, BUT
THE 00Z CAM SUITE ALMOST UNIVERSALLY SUGGESTS THE STORMS
DEVELOPING OVER CENTRAL KS WILL PROVIDE THE BETTER CHANCE. THIS
ALSO MEANS THAT OUR LOCAL STORM CHANCES WILL ARRIVE LATER INTO
MONDAY MORNING THAN PREVIOUSLY FORECAST, WHICH, IF THAT
VERIFIES, WILL HAVE IMPLICATIONS ON INSTABILITY THIS AFTERNOON.
A WOFS RUN FOCUSED ON CNTRL KS HAS A STRONG PAINTBALL SIGNAL
(CONSISTENT SIGNAL ACROSS INDIVIDUAL MEMBERS) FOR AN MCS TO BE
LOCATED OVER NORTH/CNTRL MO AT 09Z/4AM MON. INDIVIDUAL MEMBERS
OF BOTH THE 00Z HREF AND REFS SHOW THIS ACTIVITY SPILLING INTO
IL FROM THE WEST BETWEEN SUNRISE AND MIDDAY, BUT THESE MODELS DO
APPEAR A TAD SLOWER THAN WHAT IS DEPICTED BY WOFS. ULTIMATELY,
CONFIDENCE HAS INCREASED THAT WE WILL BE DEALING WITH EXTENSIVE
CLOUD COVER AND AREAS OF PRECIP ACROSS CNTRL IL THIS MORNING.
SURFACE- BASED INSTABILITY AHEAD OF THIS MCS SHOULD BE LIMITED,
BUT AT LEAST MINOR ELEVATED INSTABILITY AND A STRONGLY SHEARED
ENVIRONMENT ARE EXPECTED. TOWARDS LATE MORNING, SW FLOW
ADVECTING THE EML PLUME NORTHWARD COULD RESULT IN AN UPTICK IN
MUCAPE/STORM INTENSITY. THE MAIN CONCERN WITH THE MORNING
ACTIVITY WOULD BE ISOLATED INSTANCES OF LARGE HAIL OR STRONG
THUNDERSTORM WIND GUSTS. BASED ON THE CURRENT CAM DEPICTION OF
THESE MORNING STORMS, IT APPEARS PROBABLE THAT AN OUTFLOW
BOUNDARY OR EFFECTIVE FRONT WILL BE ESTABLISHED TO THE SOUTH OF
THE STORMS. GUIDANCE FAVORS THIS OCCURRING SOMEWHERE NEAR OR
BETWEEN THE I-72 AND I-70 CORRIDORS, BUT WHERE IT EXACTLY IT
OCCURS IS LOW CONFIDENCE.
* AFTERNOON/EVENING SEVERE STORM OUTLOOK *
SEVERE STORMS ARE STILL EXPECTED THIS AFTERNOON AND EVENING, BUT
WHERE, HOW INTENSE, AND THE ASSOCIATED HAZARDS TYPES WILL ALL
DEPEND ON THE PLACEMENT OF THE EFFECTIVE FRONT AND THE DEGREE OF
ATMOSPHERIC RECOVERY AFTER THE MORNING CONVECTION. DYNAMIC WIND
FIELDS ARE EXPECTED IN RESPONSE TO THE NEGATIVELY TILTED
TROUGH, WITH CLOCKWISE CURVED HODOGRAPHS AND 850MB WIND FIELDS
INCREASING OVER 60 KTS BY THIS AFTERNOON, SO WIND SHEAR WILL BE
STRONG AREA- WIDE. CONTINUED ADVECTION OF THE EML PLUME SHOULD
ALSO RESULT IN MODERATE TO HIGH MUCAPES BUILDING AHEAD OF A COLD
FRONT ENCROACHING FROM THE WEST DURING THE LATE
AFTERNOON/EVENING. THIS SHOULD SET THE STAGE FOR AT LEAST
SCATTERED SEVERE STORMS (LARGE HAIL/DAMAGING WINDS) ALONG THE
COLD FRONT, ALTHOUGH THE AMOUNT OF SFC INSTABILITY REMAINS A
MAJOR POINT OF UNCERTAINTY. STRONG LINEAR FORCING, PLENTIFUL
SYNOPTIC SCALE ASCENT, AND SHEAR VECTOR CROSSING ANGLES LESS
THAN 45 DEGREES FAVOR A LINEAR/QUASI-LINEAR STORM MODE ALONG THE
COLD FRONT.
AS NOTED ABOVE, THE MORNING CONVECTION FAVORS AN OUTFLOW
BOUNDARY BEING DRAPED SOMEWHERE ACROSS THE ILX CWA EARLY THIS
AFTERNOON. CAMS HAVE CAUGHT ON TO THIS, AND SHOW LOW SURFACE-
BASED INSTABILITY NORTH OF THIS FEATURE. MY INCLINATION IS THAT
MANY OF THESE CAMS MAY NOT BE AGGRESSIVE ENOUGH IN THE SOUTHWARD
PLACEMENT OF THIS BOUNDARY, BUT PERHAPS STRONG SYNOPTIC
SOUTHERLY FLOW HELPS KEEP THE COLD OUTFLOW FROM SURGING AWAY
FROM THE STORMS, AND REINFORCES A MORE NORTHWARD PLACEMENT OF
THAT BOUNDARY. AT ANY RATE, THERE IS SKEPTICISM THAT ENOUGH
RECOVERY WILL OCCUR NORTH OF THIS FEATURE TO SUPPORT SIGNIFICANT
SURFACE-BASED SEVERE HAZARDS, WHILE AREAS NEAR/SOUTH OF THIS
FEATURE WILL FACE A SIGNIFICANT ALL-HAZARDS SEVERE THREAT DURING
THE AFTERNOON/EVENING. FORECAST SOUNDINGS FROM NEAR AND SOUTH
OF THE EFFECTIVE FRONT SHOW STRONG INSTABILITY, SATURATED LOW
LEVELS (CLOUD BASES/LCLS BELOW 500M), AND ROBUST 0-1 KM SHEAR
(40 KTS) AND HELICITY (300+ J/KG), WITH THE HELICITY MAXIMIZED
NEAR THE EFFECTIVE FRONT. THIS ENVIRONMENT WOULD POSE A
SIGNIFICANT RISK OF TORNADOES. UNFORTUNATELY, THE DELINEATING
LINE BETWEEN THESE TWO REGIMES MAY NOT BECOME CLEAR UNTIL EARLY
AFTERNOON.
IN TERMS OF TIMING, CAMS SUGGEST THE FRONT AND ASSOCIATED STORMS
REACH THE IL RIVER BETWEEN 23-00Z (6-7 PM), I-55 BETWEEN 00-01Z
(7-8 PM), AND I-57 BETWEEN 01-02Z (8-9 PM). THAT TIMING ALSO
HIGHLIGHTS A FAST STORM MOTION (OVER 50 MPH), RESULTING IN
LIMITED SHELTERING TIME IN THE EVENT OF QUICK LINE-EMBEDDED
TORNADIC DEVELOPMENT. REMAIN WEATHER AWARE TODAY, AND CONTINUE
TO CHECK FOR FORECAST UPDATES AS THE RELEVANT BOUNDARY PLACEMENT
COMES INTO BETTER FOCUS.
AN ENHANCED RISK (LEVEL 3 OF 5) REMAINS IN PLACE FOR THE ENTIRE
ILX COVERAGE AREA, BUT AREAS JUST NORTH OF OUR CWA WERE LOWERED
TO A SLIGHT RISK (LEVEL 2 OF 5). CURRENT INDICATIONS BASED ON
THE LATEST CAMS ARE THAT THE TORNADO THREAT AREA IS HIGHEST
OVER THE SOUTHERN HALF OF OUR FORECAST AREA. THE ADJUSTMENT TO
SPC'S TORNADO CONDITIONAL INTENSITY LEVELS ALIGN WITH OUR
THINKING, WITH THE CIG2 AREA NOW FOCUSED ACROSS THE SOUTHERN
HALF OF THE STATE OF IL.
* HYDROLOGIC CONSIDERATIONS *
ENSEMBLE MEMBERS DEPICT PWAT VALUES INCREASING TO 1.4 TO 1.6"
ACROSS THE WARM SECTOR TODAY, WHICH IS CONSISTENT WITH UPSTREAM
VALUES CURRENTLY NOTED IN THE RAP-BASED OBJECTIVE ANALYSIS.
SUCH VALUES ARE NEAR THE MAX OF THE ILX OBSERVED SOUNDING
CLIMATOLOGY FOR LATE APRIL. HREF LPMM CONTINUES TO OUTPUT
LOCALIZED RAINFALL AMOUNTS OF 1.5 TO 3". THIS COULD LEAD TO A
FEW INSTANCES OF FLASH FLOODING. THE EVENING STORMS ALONG THE
COLD FRONT WILL BE FAST MOVING, SO THE GREATEST CONCERN WILL BE
ACROSS AREAS WHERE ANY MORNING CONVECTION TRAINS.
* SYNOPTIC WINDS & BLOWING DUST POTENTIAL *
BREEZY SOUTHERLY WINDS ARE EXPECTED AS THE PRESSURE GRADIENT
TIGHTENS IN RESPONSE TO THE SFC LOW TRACKING NORTHWEST OF OUR
AREA. HOWEVER, WITH GREATER CLOUD COVER AND PRECIP COVERAGE
DURING THE MORNING, THE EXPECTATION IS THAT BOUNDARY LAYER
MIXING WILL BE LESS ROBUST THAN PREVIOUSLY FORECAST, WHICH WOULD
LIMIT THE EXTENT OF ADVISORY LEVEL (45+ MPH) WIND GUSTS.
BETWEEN INCREASING RAIN CHANCES THIS MORNING AND LOWER WIND
GUSTS, THE BLOWING DUST CONCERN IS DEFINITELY LOWER THAN
PREVIOUSLY THOUGHT, ALTHOUGH LIKE EVERYTHING ELSE IN THE
FORECAST THE POTENTIAL IS NOT ZERO, AND IT HINGES ON THE
EVOLUTION OF THESE MORNING STORMS.
*** REST OF THE WEEK ***
FOLLOWING THE COLD FROPA TONIGHT, EXPECT COOLER CONDITIONS THE
REST OF THE WEEK, WITH HIGHS GENERALLY IN THE 60S THROUGH SAT.
THE BAROCLINIC ZONE IS EXPECTED TO BE JUST SOUTH OF THE ILX CWA
INTO TUES AS ANOTHER WAVE SWINGS TOWARDS THE REGION TUES PM.
POPS INCREASE WITH SOUTHEAST EXTENT TUES EVE, FROM 30% ALONG THE
IL RIVER VALLEY TO OVER 80% SOUTH OF I-70. DESPITE CONTINUED
STRONG WIND SHEAR, THE SFC FRONT BEING SOUTH OF OUR CWA WILL
RESULT IN NO SURFACE-BASED INSTABILITY, AND THE ELEVATED
INSTABILITY IS LOW (LESS THAN 500 J/KG), THUS SEVERE STORMS ARE
NOT EXPECTED. IN TERMS OF RAINFALL AMOUNTS, THE NBM SUGGESTS A
50-70% CHANCE OF A HALF INCH OF RAIN SOUTH OF I-70, DECREASING
TO JUST A 20% CHANCE OF OVER A HALF INCH OF RAIN ALONG AND NORTH
OF I-72/DANVILLE.
DURING THE LATTER HALF OF THE WORK WEEK, UPPER TROUGHING SHIFTS
TO THE EASTERN US/CANADA, WITH AN EMBEDDED SHORTWAVE DIGGING
TOWARDS CNTRL IL THURS EVE. AN ASSOCIATED COLD FRONT COULD OFFER
A CHANCE FOR LIGHT PRECIP (15%), ALTHOUGH LIMITED MOISTURE
RETURN AHEAD OF THIS SYSTEM SUGGESTS PWATS WILL BE LESS THAN
0.5". AS A RESULT OF THIS FRONT, FRI/FRI NIGHT APPEAR LIKE THE
COOLEST PERIOD IN THE FORECAST, WITH HIGHS IN THE UPPER 50S/LOW
60S AND LOWS IN THE UPPER 30S. WE WILL NEED TO KEEP AN EYE ON
THE FROST POTENTIAL FRIDAY NIGHT, BUT FOR NOW GUIDANCE HAS THE
PROBABILITY OF LOWS BELOW 36F LESS THAN 30%.
AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 1224 AM CDT MON APR 27 2026
EVOLUTION OF THUNDER CHANCES AT THE TERMINALS WILL BE A
SIGNIFICANT CHALLENGE THROUGH THE PERIOD, PRIMARILY FOCUSED
BETWEEN 12Z AND 02Z. THERE LOOKS TO BE A COUPLE DIFFERENT
PERIODS OF FOCUS, FIRST FROM 15-19Z AND THEN WITH A COLD
FRONT FROM ABOUT 22-02Z. OF THESE, THE LATTER PERIODS ARE MOST
LIKELY TO HAVE WINDS CLOSE TO SEVERE CRITERIA, ACCOMPANIED BY
MVFR OR IFR CONDITIONS IN THE HEAVIEST STORMS. CEILINGS IMPROVE
FROM WEST TO EAST DURING THE EVENING, AS A CLEARING SLOT WORKS
ITS WAY THROUGH CENTRAL ILLINOIS.
WINDS WILL BE PICKING UP OVERNIGHT, WITH FREQUENT GUSTS 30-35
KNOTS DURING THE AFTERNOON. A GRADUAL TREND FROM SOUTHEAST TO
SOUTHWEST IS EXPECTED THROUGH THE COURSE OF THE DAY.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...ERWIN
DISCUSSION...ERWIN
AVIATION...GEELHART
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