846
FXUS63 KLSX 201720
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
ISSUED BY NATIONAL WEATHER SERVICE LINCOLN IL
1220 PM CDT TUE MAY 20 2025
KEY MESSAGES
- THERE IS A CHANCE FOR ONE MORE ROUND OF SEVERE THUNDERSTORMS
THIS AFTERNOON INTO EARLY EVENING PRIMARILY ACROSS PARTS OF
SOUTHEAST AND EAST CENTRAL MISSOURI AS WELL AS SOUTHWEST AND
SOUTH CENTRAL ILLINOIS.
- COOLER AND MUCH LESS ACTIVE WEATHER IS EXPECTED FOR THE
REMAINDER OF THE FORECAST INTO EARLY NEXT WEEK.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 1219 PM CDT TUE MAY 20 2025
(THROUGH LATE TONIGHT)
ISSUED AT 305 AM CDT TUE MAY 20 2025
THE LONG WAVE TROUGH OVER THE GREAT PLAINS IS BECOMING NEGATIVELY
TILTED AND WILL LIFT INTO THE UPPER MIDWEST TODAY. THE SURFACE
LOW WILL MOVE FROM EASTERN KANSAS/NEBRASKA INTO IOWA BY THIS
AFTERNOON, AND THE ASSOCIATED COLD FRONT WILL SWEEP THROUGH
MISSOURI BY LATE AFTERNOON/EARLY EVENING, AND THEN THROUGH
ILLINOIS BY MIDNIGHT. SHORT RANGE GUIDANCE BUILDS INSTABILITY BACK
UP AHEAD OF THE FRONT TODAY, WITH MLCAPE AS HIGH AS 2000-2200
J/KG AND 0-6KM SHEAR OF 40- 50KTS ACROSS EAST CENTRAL AND
SOUTHEAST MISSOURI INTO SOUTHWEST AND SOUTH CENTRAL ILLINOIS.
FORECAST SOUNDINGS SHOW A WEAK CAP THAT ERODES IN SOME MODELS BUT
STAYS FIRM IN OTHERS. CONVERGENCE ALONG THE FRONT STILL DOESN'T
LOOK THAT STRONG, BUT SEVERAL SHORT RANGE MODELS DEVELOP
CONVECTION AHEAD OF THE FRONT DURING THE MID-LATE AFTERNOON
PRIMARILY IN ILLINOIS. HODOGRAPHS DO NOT SHOW MUCH CURVATURE, BUT
THE STRENGTH OF THE SHEAR AND INSTABILITY SUGGEST SUPERCELLS WILL
BE THE INITIAL CONVECTIVE MODE. STRAIGHT HODOGRAPHS WILL ENCOURAGE
SPLITS, SO DEPENDING ON THE COVERAGE THERE COULD BE MERGERS AND
UPSCALE GROWTH, HOWEVER THAT MAY NOT OCCUR UNTIL THE STORMS HAVE
EXITED OUR FORECAST AREA DURING THE EARLY EVENING.
CARNEY
LONG TERM /THURSDAY THROUGH MONDAY/
ISSUED AT 1219 PM CDT TUE MAY 20 2025
(WEDNESDAY THROUGH MONDAY)
ISSUED AT 305 AM CDT TUE MAY 20 2025
THE WEATHER FOR WEDNESDAY THROUGH NEXT MONDAY LOOKS MUCH MORE BENIGN
THAN WHAT WE'VE BEEN EXPERIENCING FOR THE PAST SEVERAL DAYS. A HIGH
AMPLITUDE PATTERN DOMINATED BY A LONG WAVE TROUGH OVER EASTERN NORTH
AMERICA AND A RIDGE OVER MUCH OF THE CENTRAL AND WESTERN PORTION OF
THE CONTINENT. MEDIUM RANGE GUIDANCE KEEPS OUR FORECAST AREA IN
NORTHWEST FLOW FOR MOST OF THE PERIOD. AT LEAST TWO OR THREE SHORT
WAVES PASS OVER THE AREA, ONE FRIDAY, AND ANOTHER TWO SATURDAY INTO
SUNDAY. THESE WAVES FORCE CYCLOGENESIS OVER THE PLAINS AND TURN THE
LOW LEVEL FLOW BACK TO THE SOUTH ACROSS THE LOWER AND MID
MISSISSIPPI VALLEY PRODUCING MODERATE TO STRONG LOW LEVEL MOISTURE
CONVERGENCE. THE DETERMINISTIC GFS AND ECMWF PRINT OUT SEVERAL
INCHES OF PRECIPITATION ACROSS PARTS OF MISSOURI INTO SOUTHERN
ILLINOIS. HOWEVER, THE LREF AND NBM FOCUS MORE ON SOUTHWEST
MISSOURI INTO THE LOWER MISSISSIPPI VALLEY. THE 75TH AND 90TH
PERCENTILES DO PAINT A BROAD SWATH OF 2+ INCH QPF ALONG AND SOUTH OF
I-70 THOUGH, SO THERE COULD BE SOME WATER ISSUES TO DEAL WITH THIS
WEEKEND. THE GOOD NEWS IS THAT OUR FORECAST AREA STAYS ON THE COOL
SIDE OF THE SURFACE BOUNDARY. VERY LITTLE INSTABILITY WILL BE
AVAILABLE, AND WHILE THERE MAY BE THUNDERSTORMS AT TIMES, THE STORMS
SHOULD NOT BE SEVERE. TEMPERATURES WILL RUN COOL THROUGH THE PERIOD
WITH HIGHS MAINLY IN THE MID 60S TO AROUND 70 AND LOWS IN THE MID
40S TO LOW AND MID 50S.
CARNEY
AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 1220 PM CDT TUE MAY 20 2025
A MESOSCALE COMPLEX SPINNING OVER NORTHEAST MISSOURI EARLY THIS
AFTERNOON WILL BE THE FOCUS FOR ANY THUNDERSTORMS THAT DEVELOP OVER
THE NEXT FEW HOURS. THE COLD FRONT HAS ALREADY MOVED THROUGH WESTERN
AIRFIELDS (KCOU, KJEF), KEEPING ANY STORM ACTIVITY EAST OF THEM
THROUGH THE TAF PERIOD. STORM TIMING FOR LOCATIONS FURTHER EAST WILL
BE HIGHEST BETWEEN 18-20Z, WHICH IS WHEN TEMPO GROUPS HAVE BEEN
ADDED. THE COLD FRONT WILL CONTINUE TO SPREAD EAST THIS AFTERNOON,
SHIFTING WINDS TO THE WEST BEHIND IT. WINDS WILL STAY BREEZY THROUGH
THE OVERNIGHT HOURS THEN BECOME GUSTY BY WEDNESDAY MORNING AS THEY
VEER TO THE NORTHWEST ON THE BACKSIDE OF THE SURFACE LOW.
POCKETS OF MVFR CEILINGS WILL BE MOST COMMON WITHIN THE VICINITY OF
THE MESOSCALE COMPLEX AND WITH THUNDERSTORM ACTIVITY THIS AFTERNOON.
THERE IS ABOUT A 40-50% CHANCE THAT CEILINGS WILL DROP BACK BELOW 3K
FT IN WEST-CENTRAL IL AFTER 06Z TONIGHT. ELECTED NOT TO ADD A
PREVAILING GROUP FOR THIS AT KUIN AS OF NOW, BUT THIS MAY BE NEEDED
IN FUTURE TAF UPDATES.
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
SHORT TERM...
LONG TERM...
AVIATION...WFO ILX
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