395
FXUS63 KILX 201933
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
233 PM CDT TUE MAY 20 2025
KEY MESSAGES
- SEVERE THUNDERSTORMS CAPABLE OF ALL HAZARDS (TORNADOES, LARGE
HAIL, DAMAGING WINDS, AND LOCALLY HEAVY RAINFALL) WILL PROGRESS
WEST TO EAST ACROSS ILLINOIS THIS AFTERNOON, EXITING INTO
INDIANA DURING THE EVENING. AS OF 2PM, A TORNADO WATCH WAS IN
EFFECT FOR MOST AREAS ALONG AND NORTH OF I-70.
- A PROLONGED PERIOD OF BELOW NORMAL TEMPERATURES IS EXPECTED
BEGINNING WEDNESDAY AND LASTING INTO NEXT WEEK. DURING THIS
PERIOD, HIGH TEMPERATURES WILL STRUGGLE TO REACH 70 DEGREES.
- SOME LIGHT SHOWERS ARE POSSIBLE WEDNESDAY (20-30%) AND THURSDAY
(20%), THEN A BETTER CHANCE FOR RAIN ARRIVES OVER THE WEEKEND
(40- 60%). AT THIS TIME, THE SEVERE THUNDERSTORM/FLASH FLOODING
POTENTIAL APPEARS LOW.
DISCUSSION
ISSUED AT 225 PM CDT TUE MAY 20 2025
*** THROUGH TONIGHT ***
A TORNADO WATCH HAS BEEN ISSUED FOR MUCH OF THE CWA UNTIL 8PM/01Z
(THOUGH THE THREAT WILL BE ENDING FROM WEST TO EAST DURING THE
LATE AFTERNOON/EVENING), AS AN APPROACHING MCV HAS SPAWNED AN
ARCING BAND OF CONVECTION. A WARM FRONT WAS ALSO DRAPED JUST NORTH
OF THE I-74 CORRIDOR AS OF 19Z/2PM, LEAVING THE MAJORITY OF THE
ILX CWA IN THE WARM SECTOR. WITHIN THE WARM SECTOR, TEMPS HAVE
CLIMBED INTO THE MID OR UPPER 70S, WHICH IS NEAR OR ABOVE WHAT
MODEL GUIDANCE SUGGESTED THIS MORNING. RAP- BASED MESOA FIELDS
SUGGEST SBCAPE VALUES HAVE CLIMBED ABOVE 1500 J/KG. IT SEEMS THE
FACTORS SUPPORTING LARGE HAIL (STEEP MID- LEVEL LAPSE RATES OF 8
DEGC/KM IN THE 500-700MB LAYER PER THE 18Z ILX SOUNDING; WIDE CAPE
IN THE HAIL GROWTH ZONE) ARE WINNING OUT OVER SOME OF THE
POTENTIAL MITIGATING FACTORS, AS SOME OF THE STORMS HAVE ALREADY
PRODUCED 2" HAIL IN MORGAN COUNTY. BASED ON THE KILX VAD, LOW-
LEVEL WINDS ARE FAIRLY UNIDIRECTIONAL, RESULTING IN 0-1KM SRH LESS
THAN 100 J/KG AT LINCOLN AS OF THIS WRITING. HOWEVER, KILX IS
STILL FAIRLY REMOVED FROM THE INFLUENCE OF THE MCV, WHICH WILL ACT
TO LOCALLY BACK THE SFC WINDS, AND THUS ITS REASONABLE THAT
MODERATE SRH VALUES OF OVER 100 J/KG ARE PRESENT NEAR THE ARCING
BAND OF STORMS. WHILE DEEP LAYER SHEAR VECTORS APPEAR RATHER
ORTHOGONAL TO THE ARCING CONVECTION, THE ROBUST FORCING HAS LED TO
CONVECTIVE CLUSTERS, RATHER THAN DISCRETE CELLS. ALL OF THIS
ACTIVITY WILL PROGRESS EAST THROUGH THE EVENING, POSING A RISK OF
ALL SEVERE HAZARDS, AND INSTABILITY COULD RISE FURTHER ACROSS
EASTERN IL BEFORE STORMS MOVE THROUGH THIS EVENING. STORMS SHOULD
REACH THE IL/IN BETWEEN 6-8PM, AND IT DOES NOT APPEAR THAT THERE
WILL BE A LLJ ONSET THIS EVENING, SO NO OBVIOUS INCREASE IN THE
TORNADO POTENTIAL IN THAT REGARD.
WE WILL BE MONITORING FOR THE DEVELOPMENT OF ANY FLASH FLOODING
GIVEN THAT OVERNIGHT RAINFALL TOTALS RANGED GENERALLY FROM 0.75-
2.00". PWAT VALUES ARE AROUND 1.3", NOT QUITE AS HIGH AS WHAT WAS
IN PLACE DURING THE OVERNIGHT HOURS. STORM MOTIONS ARE FAIRLY
PROGRESSIVE IN THE ILX CWA (20-35 MPH TO THE NORTHEAST), AND THESE
MOTIONS SHOULD HELP LIMIT THE FLOODING POTENTIAL UNLESS TRAINING
OCCURS.
WINDS THIS EVENING WILL SWING AROUND TO WESTERLY, AND SOME
LINGERING SHOWERS (LITTLE TO NO THUNDER) ARE POSSIBLE (20-30%
CHANCE) MAINLY NORTH OF I-72. LOWS FALL INTO THE LOW 50S.
*** WEDNESDAY AND BEYOND ***
MUCH OF THE LONG TERM FORECAST PERIOD WILL BE CHARACTERIZED BY
UPPER LEVEL TROUGHING OVER THE EASTERN GREAT LAKES/NEW ENGLAND.
THIS WILL TRANSLATE TO SEVERAL DAYS OF COOLER THAN NORMAL
TEMPERATURES LOCALLY WITH HIGHS GENERALLY IN THE 60S EACH DAY
THROUGH THE WEEKEND. SOME LIGHT SHOWERS/DRIZZLE ARE POSSIBLE
(20-30%) WED/THURS, MAINLY NORTH OF I-74. IT WILL BE BREEZY
THROUGH THE END OF THE WORK WEEK AS A SFC LOW SLOWLY LIFTS
NORTHEAST OVER THE EASTERN GREAT LAKES, BUT WINDS SPEEDS SHOULD
TREND LOWER EACH DAY AFTER WEDNESDAY (WHEN GUSTS OF UP TO 30 MPH
ARE FORECAST). OVERALL, SIGNIFICANT WEATHER IMPACTS APPEAR
UNLIKELY THROUGH THE END OF THE WEEK. FORECAST LOWS SHOULD STAY
WARM ENOUGH (MID 40S) TO AVOID ANY FROST ISSUES DURING THIS COOL
SPELL. PRECIP CHANCES RETURN/INCREASE LATE IN THE WEEKEND,
ALTHOUGH GUIDANCE HAS BEEN INCONSISTENT IN THE EVOLUTION OF THE
ASSOCIATED SYSTEM. FOR NOW, THE BLENDED GUIDANCE HAS A 40-60%
CHANCE OF RAIN SAT-SUN. EVEN INTO NEXT WEEK, THE DETERMINISTIC NBM
KEEPS FORECAST HIGHS NEAR 70F, BELOW NORMAL FOR THIS TIME OF
YEAR.
ERWIN
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1227 PM CDT TUE MAY 20 2025
A WARM FRONT IS NEAR THE I-74 CORRIDOR, WITH IFR CEILINGS NORTH OF
THE FRONT AND MVFR/VFR CEILINGS TO THE SOUTH. A SFC LOW WILL TRACK
ACROSS THE AREA THIS AFTERNOON RESULTING IN SCATTERED
SHOWERS/STORMS SHIFTING FROM WEST TO EAST. THESE SHOULD DEPART TO
THE EAST OF KCMI BY 23Z. SCATTERED LIGHT SHOWERS COULD CONTINUE
INTO THE EVENING, BUT THE THREAT OF THUNDER SHOULD END AFTER 23Z,
OR 00Z AT THE LATEST. OVERNIGHT ANOTHER PUSH OF MVFR, OR PERHAPS
IFR, CEILINGS ARRIVES FROM THE NORTH. WINDS WILL HAVE A SOUTHERLY
COMPONENT THIS AFTERNOON, THEN SHIFT TO WESTERLY TONIGHT AND
BECOME BREEZY INTO THE DAYTIME HOURS ON WEDNESDAY.
ERWIN
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
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