441
FXUS63 KLSX 191953
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
253 PM CDT MON MAY 19 2025
KEY MESSAGES
- WIDESPREAD THUNDERSTORMS ARE EXPECTED THIS EVENING, SOME OF
WHICH COULD BE STRONG TO SEVERE WITH DAMAGING WINDS, LARGE HAIL,
AND A FEW TORNADOES. THERE IS ALSO A SUBSEQUENT CONDITIONAL
RISK OF LOCALLY HEAVY RAINFALL AND ISOLATED FLASH FLOODING
OVERNIGHT.
- A FEW STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE AGAIN TUESDAY
AFTERNOON/EARLY EVENING, BUT THE OVERALL RISK IS LOWER THAN
THIS EVENING.
SHORT TERM
(THROUGH LATE TUESDAY NIGHT)
ISSUED AT 252 PM CDT MON MAY 19 2025
A WARM FRONT CURRENTLY STRETCHES FROM JUST NORTH OF KANSAS CITY
THROUGH CENTRAL MO AND INTO FAR SOUTHWESTERN IL. THIS FRONT WILL
CONTINUE TO LIFT SLOWLY NORTHWARD ACROSS MORE OF THE CWA, MARKING
THE NORTHERN LIMIT OF RICHER LOW-LEVEL MOISTURE AND INSTABILITY.
WITH BOUTS OF SURFACE HEATING, SHORT-TERM MODEL GUIDANCE ADVERTISE
MLCAPE OF 2000+ J/KG EXTENDING TO NEAR THE WARM FRONT BY THIS
EVENING.
THUNDERSTORMS, INCLUDING SUPERCELLS, ARE ALREADY ONGOING
ACROSS NORTHEASTERN OK/SOUTHEASTERN KS EARLY THIS AFTERNOON, WITH
THUNDERSTORMS ONLY INCREASING IN COVERAGE ACROSS THE WESTERN HALF OF
MO IN ASSOCIATION WITH A PASSING SHORTWAVE TROUGH AND MINIMAL
CONVECTIVE INHIBITION. AS A RESULT, THUNDERSTORMS WILL LIKELY BE
GROWING UPSCALE INTO ONE OR MORE MCSS THAT TRACK NORTHEASTWARD
ACROSS THE CWA, REACHING CENTRAL MO AS EARLY AS 22Z. AHEAD OF THESE
THUNDERSTORMS, MORE ISOLATED THUNDERSTORMS ARE POSSIBLE WITHIN BROAD
LOW-LEVEL ISENTROPIC ASCENT; HOWEVER, THE STRENGTH OF THESE
THUNDERSTORMS MAY BE LIMITED EARLY BY A WEAKNESS IN MID-LEVEL WINDS
AND EFFECTIVE WIND SHEAR WITH AN AMPLIFYING, IMMEDIATELY UPSTREAM
RIDGE. THROUGH THIS EVENING, DEEP-LAYER AND EFFECTIVE WIND SHEAR
WILL INCREASE TO 35 TO 50 KT WITH SOME LOW-LEVEL HODOGRAPH
CURVATURE, SUFFICIENT FOR A MIXED MODE OF MULTICELL/QLCS AND A FEW
TRANSIENT SUPERCELLS. CONSIDERING CONVECTIVE MODE, DAMAGING WINDS,
LARGE HAIL, AND A FEW TORNADOES ALL REMAIN HAZARDS WITH SEVERE
THUNDERSTORMS. THE GREATEST THREAT IS ACROSS CENTRAL MO, DECREASING
GRADUALLY EASTWARD ACROSS THE MISSISSIPPI RIVER WITH INSTABILITY
GENERALLY DECREASING WITH TIME AND WITH NORTH/EAST EXTENT. THE
LONGEVITY OF THE SEVERE THUNDERSTORM THREAT WILL ALSO DEPEND ON HOW
QUICKLY THUNDERSTORMS OVERTURN INSTABILITY AND PROPAGATE ACROSS THE
CWA BUT THE GENERAL CONSENSUS IS FOR THE THREAT TO WANE AROUND 04 TO
05Z. WITH FAVORABLE INGREDIENTS FOR HIGH RAINFALL RATES (I.E., DEEP-
WARM CLOUD DEPTHS 10 TO 12 KFT AND ANOMALOUS PWAT OVER 1.6") AS
WELL, ISOLATED FLASH FLOODING IS POSSIBLE WHERE ANY THUNDERSTORM
TRAINING OR BACKBUILDING CAN TAKE PLACE. THE HEAVY RAINFALL/FLASH
FLOOD THREAT IS LARGELY CONDITIONAL ON A FAVORABLE INTERACTION
BETWEEN A SOUTHERLY LLJ AND THE SOUTHERN FLANK OF ANY MCS IN THE
ABSENCE OF PRE-EXISTING BOUNDARY ALIGNED WITH THE SOUTHWESTERLY DEEP-
LAYER FLOW.
WITH A MORE POTENT UPPER-LEVEL TROUGH PIVOTING ACROSS THE MID-
MISSISSIPPI RIVER VALLY TUESDAY MORNING, AT LEAST SCATTERED SHOWERS
AND THUNDERSTORMS COULD BE ONGOING, DEPENDING ON HOW MUCH
INSTABILITY IS AVAILABLE. HOWEVER, BY MIDDAY/AFTERNOON, THE AXIS OF
THE TROUGH WILL ALREADY BE LIFTING TO THE NORTHEAST, LIMITING
CONFIDENCE IN COVERAGE OF REDEVELOPING THUNDERSTORMS IN THE PRESENCE
OF A WEAK CAPPING INVERSION BENEATH A SUBTLE DRY CONVEYOR BELT AND
VEERING SURFACE WINDS AHEAD OF A WEAK COLD FRONT. THEREFORE, THE
HIGHEST HREF PROBABILITIES OF MEASURABLE RAINFALL (40 TO 60 PERCENT)
ARE ALONG/EAST OF THE MISSISSIPPI RIVER WITHIN RELATIVELY STRONGER
ASCENT. CONVERSELY, MOST SHORT-TERM MODEL GUIDANCE INDICATE THAT THE
DRY CONVEYOR BELT COMBINED WITH RESIDUAL MOISTURE AND HEATING WILL
SUPPORT AROUND 1000 J/KG OF MLCAPE DURING THE AFTERNOON WITH AROUND
40 KT OF EFFECTIVE WIND SHEAR. THEREFORE, THUNDERSTORMS MAY ORGANIZE
INTO A FEW TRANSIENT SUPERCELLS AND/OR SMALL THUNDERSTORM CLUSTERS,
SOME OF WHICH COULD BE SEVERE AND CAPABLE DAMAGING WINDS, LARGE
HAIL, AND PERHAPS A BRIEF TORNADO DURING THE AFTERNOON/EARLY EVENING.
PFAHLER
LONG TERM
(WEDNESDAY THROUGH NEXT MONDAY)
ISSUED AT 252 PM CDT MON MAY 19 2025
QUIETER, DRIER, AND MORE TRANQUIL CONDITIONS WILL PREVAIL WEDNESDAY
INTO FRIDAY AS UPPER-LEVEL CYCLONE FLOW BECOMES ESTABLISHED ACROSS
THE MID-MISSISSIPPI RIVER VALLEY IN RESPONSE TO LONGWAVE TROUGHING
OVER THE GREAT LAKES AND NORTHEAST. THIS PATTERN WILL ALSO USHER A
COOL AIRMASS (850-HPA TEMPERATURES BELOW 10TH PERCENTILE) INTO THE
REGION UPON STEADY LOW-LEVEL CAA, RESULTING IN BELOW AVERAGE
TEMPERATURES.
GLOBAL MODEL GUIDANCE ARE IN AGREEMENT THAT A RELATIVELY MORE ACTIVE
PATTERN WILL RETURN TO THE CENTRAL CONUS OVER THE WEEKEND AS UPPER-
LEVEL FLOW TRANSITIONS TO BROADLY ANTICYCLONIC/QUASI-ZONAL WITH
MULTIPLE MID-LEVEL PERTURBATIONS/SHORTWAVE TROUGHS EXCITING ROUNDS
OF SHOWERS AND THUNDERSTORMS, POSSIBLY ORGANIZED INTO MCSS THAT
TRACK NEAR A WAVERING FRONT. ALTHOUGH THERE IS UNCERTAINTY ON THE
TRACK AND FRONTAL LOCATION, THE HIGHEST PROBABILITIES OF MUCAPE OF
750+ J/KG AND 24-HOUR RAINFALL ARE TO THE SOUTHWEST OF THE CWA,
DECREASING CONFIDENCE THAT OUR CWA WILL SEE THE MOST SIGNIFICANT
IMPACTS FROM THIS PATTERN. SIMILARLY, WITH THE CWA ON THE COOL SIDE
OF THE FRONT IN THE MAJORITY OF SOLUTIONS, TEMPERATURES WILL REMAIN
BELOW AVERAGE THROUGH THE WEEKEND.
PFAHLER
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1218 PM CDT MON MAY 19 2025
SCATTERED SHOWERS AND THUNDERSTORMS WILL REACH A MINIMUM IN COVERAGE
THIS AFTERNOON ALONG WITH IMPROVEMENT FROM ANY MVFR CEILINGS TO VFR
FLIGHT CONDITIONS. HOWEVER, SHOWERS AND THUNDERSTORMS WILL INCREASE
IN COVERAGE THIS EVENING AS ONE OR MORE THUNDERSTORM CLUSTERS MOVE
NORTHEASTWARD INTO THE REGION, ACCOMPANIED BY MVFR TO IFR FLIGHT
CONDITIONS AND POSSIBLY GUSTY WINDS. THUNDERSTORMS MAY PERSIST
LONGER INTO TONIGHT THAN INDICATED IN THE CURRENT TAF, WHICH
HIGHLIGHTS THE PERIOD WITH GREATEST CHANCE OF THUNDER. LINGERING
MVFR TO IFR CEILINGS WILL LIFT AND SCATTER TUESDAY MORNING AS WINDS
VEER FROM SOUTHEASTERLY TO SOUTHWESTERLY. ADDITIONAL SHOWERS AND
THUNDERSTORMS ARE POSSIBLE ON TUESDAY, MAINLY IN SOUTHWESTERN IL
WITH MORE LIMITED COVERAGE NEAR ST. LOUIS METRO TERMINALS. FOR THIS
REASON, ONLY VCSH HAS BEEN INCLUDED AT THIS POINT.
PFAHLER
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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