615
FXUS63 KILX 130817
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
317 AM CDT MON APR 13 2026
KEY MESSAGES
- THE STRETCH OF WARM WEATHER IS EXPECTED TO LAST THROUGH
FRIDAY, WITH DAILY TEMPERATURES CLIMBING NEAR 80 DEGREES, AND
AT TIMES, THE MID-80S. BREEZY WINDS, OCCASIONALLY REACHING
25-35 MPH, WILL ACCOMPANY THIS WARM PERIOD.
- THIS WEEK WILL BE RIDDLED WITH THUNDERSTORM POTENTIAL.
TUESDAY, WEDNESDAY, AND FRIDAY CURRENTLY EXHIBIT THE HIGHEST
PROBABILITY (15-30%) OF SEVERE WEATHER.
- THERE IS ALSO POTENTIAL FOR SUBSTANTIAL ACCUMULATIVE RAINFALL
THROUGHOUT THE WEEK, WITH OUR MULTI- MODEL ENSEMBLE
PREDICTING A MEDIUM (40-60%) CHANCE OF EXCEEDING 2 INCHES
THROUGH SATURDAY IN AREAS NORTH OF INTERSTATE 72.
DISCUSSION
ISSUED AT 257 AM CDT MON APR 13 2026
PATTERN RECOGNITION
A STRONG PATTERN OF LOW-LEVEL WARM AIR ADVECTION WILL USHER IN
A WEEK OF WEATHER MORE TYPICAL OF EARLY JUNE THAN MID- APRIL,
CHARACTERIZED BY HOT AND HUMID CONDITIONS. HIGH TEMPERATURES
WILL GENERALLY REACH NEAR 80 DEGREES, AND AT TIMES, THE MID-80S.
THIS PATTERN IS DRIVEN BY AN ACTIVE UPPER- LEVEL FLOW, WITH TWO
VIGOROUS TROUGHS MOVING INLAND FROM THE WEST COAST OVER THE
NEXT SEVEN DAYS. WITH PERSISTENT TROUGHING OVER THE WESTERN U.S.
AND A CONTINUOUS NORTHWARD SURGE OF GULF MOISTURE UP THE
MISSISSIPPI VALLEY, INTERMITTENT PERIODS OF THUNDERSTORM
ACTIVITY ARE FAVORED.
HOWEVER, SIGNIFICANT FORECAST UNCERTAINTY REMAINS REGARDING THE
EXACT TIMING AND LOCATION OF THESE STORMS. VIGILANCE WILL BE
NECESSARY NOT ONLY FOR SEVERE WEATHER BUT ALSO FOR LOCALIZED
FLOODING AS SUCCESSIVE CONVECTIVE EVENTS MAY COMPOUND THROUGHOUT
THE WEEK.
MONDAY
ATMOSPHERIC INSTABILITY WILL INCREASE ACROSS THE REGION TODAY
DUE TO THE ADVECTION OF A ROBUST ELEVATED MIXED LAYER (EML)
ACROSS THE CENTRAL PLAINS TOWARD THE UPPER- MISSISSIPPI VALLEY.
THIS WILL OCCUR ATOP A VEERING LOW-LEVEL JET AXIS EXTENDING
ROUGHLY FROM CENTRAL OKLAHOMA TO SOUTHEAST WISCONSIN.
WARM AND HUMID SURFACE CONDITIONS ARE ANTICIPATED, WITH SURFACE
TEMPERATURES NEAR 80 F AND DEWPOINTS IN THE 60S. THIS BOUNDARY
LAYER ENVIRONMENT IS EXPECTED TO BOOST SURFACE-BASED CAPE TO
APPROXIMATELY 2000 J/KG, PARTICULARLY IN AREAS NEAR AND WEST OF
INTERSTATE 55.
DESPITE THE HIGH CAPE, THE OVERALL THREAT FOR THUNDERSTORMS
APPEARS LOW. RESIDUAL SUBSIDENCE AND A MARGINAL INCREASE IN MID-
LEVEL HEIGHT TENDENCIES BEHIND LAST NIGHT'S SHORTWAVE TROUGH
ARE EXPECTED TO MAINTAIN A STRONG AND PERSISTENT CAP, AS
INDICATED BY VARIOUS MODEL SOUNDINGS. GIVEN THE ABSENCE OF A
ROBUST FORCING MECHANISM, THE MOST LIKELY SCENARIO IS NO
THUNDERSTORM ACTIVITY TODAY.
ONLY THE 00Z HRRR AND ARW MODELS BREAK THE CAP, SUGGESTING
ISOLATED DEVELOPMENT NORTH OF A MACOMB TO BLOOMINGTON LINE,
PRIMARILY ACROSS NORTHERN ILLINOIS BETWEEN NOON AND 4PM. THIS
AREA IS CLOSER TO THE LOW-LEVEL JET AXIS AND IN THE VICINITY OF
THE EML/BETTER LAPSE RATES. THE CHANCE OF STORMS IS LOW
(20-40%), BUT IF THE CAP ERODES IN THIS LOCALIZED AREA, THE
FAVORABLE CAPE/SHEAR PARAMETER SPACE WOULD SUPPORT SUPERCELLS OR
MULTICELL CLUSTERS CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING
THUNDERSTORM WINDS.
TUESDAY
THE POTENTIAL FOR SEVERE CONVECTION ON TUESDAY IS CONDITIONAL,
STEMMING FROM MODERATE INSTABILITY. THIS INSTABILITY IS
SUPPORTED BY SURFACE TEMPERATURES NEAR 85 F, DEWPOINTS IN THE
60S, AND FAVORABLE MID-LEVEL LAPSE RATES, ALL OF WHICH WILL
ALIGN WITH AN INTENSIFYING MID-LEVEL JET.
HOWEVER, THE SYNOPTIC FORCING REMAINS SOMEWHAT NEBULOUS. THE
MAIN SURFACE FRONT APPEARS NORTH OF OUR FORECAST AREA; THE
POSITION OF ANY CONVECTIVE OUTFLOWS ARE CURRENTLY UNKNOWN; AND
THERE IS NO STRONG SHORTWAVE LIFTING ACROSS THE REGION.
MESOSCALE SOUNDINGS SHOW A "LOADED GUN" PROFILE, BUT THE TRIGGER
MECHANISM FOR STORM INITIATION REMAINS UNCLEAR INTO THE
AFTERNOON AND EARLY EVENING HOURS.
CONSEQUENTLY, SIGNIFICANT UNCERTAINTY EXISTS REGARDING THE
TIMING AND LOCATION OF STORM DEVELOPMENT, AND CAMS ARE
STRUGGLING TO ACCURATELY DEPICT THE INITIATION AND EVOLUTION OF
STORMS ON TUESDAY.
GLOBAL MODELS ARE INDICATING THE HIGHER PROBABILITY OF
WIDESPREAD CONVECTION LATE TUESDAY NIGHT INTO WEDNESDAY MORNING.
THIS ACTIVITY IS TIED TO A STRENGTHENING LOW-LEVEL JET AND AN
INITIAL SHORTWAVE DISTURBANCE EJECTING AHEAD OF A MORE POTENT
TROUGH TRACKING ACROSS THE LEE OF THE ROCKIES. WHILE THE EXACT
PATH OF THIS LEADING WAVE IS STILL UNCERTAIN, THE FAVORABLE
CAPE/SHEAR ENVIRONMENT IS EXPECTED TO SUPPORT ELEVATED
SUPERCELLS AND MULTICELL CLUSTERS OVER CENTRAL OR NORTHERN
ILLINOIS. POTENTIAL HAZARDS INCLUDE LARGE HAIL, ISOLATED
DOWNBURST WINDS, AND LOCALIZED HEAVY RAINFALL.
WEDNESDAY & THURSDAY
THE FORECAST FOR WEDNESDAY IS ALSO CONDITIONAL, LARGELY
DEPENDENT ON THE PERSISTENCE AND LOCATION OF CONVECTIVE
OUTFLOW/DEBRIS FROM THE PRECEDING NIGHT. THE ECMWF SUGGESTS THIS
DEBRIS MAY LINGER OVER OUR AREA THROUGH WEDNESDAY MORNING,
PRECEDING THE MAIN UPPER TROUGH. IN CONTRAST, THE GFS PLACES THE
DEBRIS FURTHER NORTH, CLOSER TO THE SURFACE FRONT. IF OUR AREA
IS LARGELY CLEAR BY WEDNESDAY MORNING, THERE IS A RISK OF SEVERE
WEATHER AND LOCALIZED FLASH FLOODING IN THE AFTERNOON. HOWEVER,
IF CONVECTIVE DEBRIS COVERS THE AREA, THE RISKS OF SEVERE
WEATHER AND FLASH FLOODING WILL BE SIGNIFICANTLY REDUCED.
REGARDLESS OF THE WEDNESDAY OUTCOME, THURSDAY LOOKS TO BE A
REGION-WIDE BREAK FROM PRECIPITATION DUE TO SYNOPTIC-SCALE
SUBSIDENCE MOVING IN BEHIND THE DEPARTING UPPER TROUGH.
THIS WEEKEND
THUNDERSTORM ACTIVITY IS THEN EXPECTED TO RETURN OVER THE
WEEKEND, SPECIFICALLY FRIDAY NIGHT INTO SATURDAY. THIS IS
ASSOCIATED WITH A COMPACT SHORTWAVE TROUGH LIFTING ACROSS THE
MID- MISSISSIPPI VALLEY AHEAD OF A PIVOTING, MORE VIGOROUS
TROUGH AND ITS ACCOMPANYING COLD FRONT. THE CAPE/SHEAR PARAMETER
SPACE ONCE AGAIN APPEARS VOLATILE ENOUGH TO SUPPORT AN
ORGANIZED SEVERE CONVECTIVE RISK, EVEN THOUGH THE FRONT APPEARS
TO PASS DURING A DIURNALLY UNFAVORABLE TIME.
FOLLOWING THE COLD FRONTAL PASSAGE, TEMPERATURES WILL COOL
SIGNIFICANTLY FROM SATURDAY NIGHT THROUGH MONDAY AS THE WARM,
MOIST AIR MASS FROM THE PREVIOUS WEEK IS FLUSHED OUT. THE LATEST
NBM DETERMINISTIC GUIDANCE SUPPORTS SUNDAY AFTERNOON HIGH
TEMPERATURES NEAR 60 DEGREES, WITH OVERNIGHT LOWS AROUND 40
DEGREES. FROST POTENTIAL IS NON-ZERO DURING THIS TIME, AND WILL
NEED TO BE MONITORED WITH SUBSEQUENT UPDATES.
AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 1156 PM CDT SUN APR 12 2026
MVFR CEILINGS WILL BUILD IN FROM THE NORTHWEST THROUGH 12Z,
AFFECTING THE CENTRAL IL TERMINALS THROUGH MIDDAY. THESE
CEILINGS ARE FORECAST TO DIURNALLY RISE ABOVE THE MVFR THRESHOLD
DURING THE EARLY AFTERNOON. SOUTHWEST WINDS WILL CONTINUE TO BE
GUSTY THROUGH THE PERIOD, NEAR 25 KT AT TIMES.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...25
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