786
FXUS63 KLSX 190850
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
350 AM CDT MON MAY 19 2025
KEY MESSAGES
- THUNDERSTORMS ARE EXPECTED TODAY AND TONIGHT. SOME OF THE STORMS
COULD BE SEVERE LATE THIS AFTERNOON AND TONIGHT WITH LARGE
HAIL, DAMAGING WINDS, AND A FEW TORNADOES. THE GREATEST THREAT
FOR SEVERE STORMS IS ACROSS CENTRAL AND NORTHEAST MISSOURI.
LOCALLY HEAVY RAINFALL IS ALSO POSSIBLE.
- THERE IS ANOTHER CHANCE FOR SEVERE THUNDERSTORMS ON TUESDAY
AFTERNOON.
SHORT TERM
(THROUGH LATE TUESDAY AFTERNOON)
ISSUED AT 346 AM CDT MON MAY 19 2025
THE LONG WAVE TROUGH OVER THE ROCKIES IS FORECAST TO BECOME
NEGATIVELY TILTED TODAY, AND LIFT NORTHEAST THROUGH THE PLAINS INTO
THE MIDWEST BY TUESDAY. THE LOW LEVEL REFLECTION WILL CONTINUE TO
PRODUCE A LOW LEVEL JET OVER THE EASTERN PLAINS INTO THE MID
MISSISSIPPI VALLEY TODAY AND TONIGHT AS IT MOVES SLOWLY THROUGH KANSAS
AND NEBRASKA AND MOVES INTO IOWA BY EARLY TUESDAY. CURRENT THINKING
IS THIS MORNING'S CONVECTION WILL CONTINUE LIFTING NORTHEAST WHILE
WEAKENING AS THE LOW LEVEL JET BACKS MORE TO THE SOUTH IN RESPONSE
TO THE MOVEMENT OF THE LOW. SHOULD SEE A RELATIVE MINIMUM OF PRECIP
WITH ONLY ISOLATED TO WIDELY SCATTERED SHOWERS FROM LATE MORNING
INTO AT LEAST MID AFTERNOON. WITH A MINIMUM OF PRECIPITATION, THE
AMOUNT OF CLOUD COVER OVER THE AREA TODAY WILL BE HIGHLY IMPACTFUL
TO HOW UNSTABLE THE ATMOSPHERE CAN GET THIS AFTERNOON. TO THAT END,
AM UNSURE HOW MUCH CLOUD COVER THERE WILL BE TODAY AS SATELLITE
IMAGERY IS SHOWING CLEARING OVER SOUTHWEST MISSOURI, HOWEVER ANOTHER
AREA OF CLOUDS IS DEVELOPING OVER NORTHWEST ARKANSAS AND IS
EXPANDING TO THE NORTH. LATEST GUIDANCE KEEPS US MOSTLY CLOUDY, BUT
STILL DEVELOPS UP TO AROUND 2000 J/KG MLCAPE BY 00Z THIS EVENING. IF
THERE'S MORE SUNSHINE, THIS INSTABILITY FORECAST COULD BE WOEFULLY
UNDERDONE. CAMS SHOW STORMS DEVELOPING OVER EASTERN KANSAS OR
WESTERN MISSOURI AND MOVING INTO CENTRAL MISSOURI BETWEEN 23-01Z. 0-
6KM SHEAR IS INITIALLY ONLY AROUND 25KTS, BUT INCREASES INCREASES TO
40-50KTS AS THE LOW LEVEL JET STRENGTHENS DURING THE EVENING. COULD
SEE SOME DISCRETE STORMS INITIALLY WITH ALL SEVERE THREATS POSSIBLE,
BUT 0-3KM SHEAR LOOKS LIKE IT WILL BE NEARLY PARALLEL TO STORM
MOTIONS SO EXPECT STORMS TO GROW UPSCALE INTO AN MCS FAIRLY QUICKLY.
THE RAP AND GFS DECREASE INSTABILITY QUICKLY DURING THE EVENING WITH
MUCAPE ONLY AROUND 1000 J/KG BY MID TO LATE EVENING. THE SEVERE
THREAT SHOULD THEREFORE DECREASE AFTER THE FIRST ROUND OF STORMS
MOVES THROUGH. LOCALLY HEAVY RAINFALL WILL THEN BECOME THE PRIMARY
THREAT FOR THE REST OF THE NIGHT.
THE COLD FRONT ASSOCIATED WITH THIS SYSTEM WILL THEN MOVE THROUGH
THE AREA ON TUESDAY. CONVERGENCE ALONG THE FRONT STILL DOESN'T LOOK
PARTICULARLY STRONG, AND FORECAST SOUNDINGS SHOW A SMALL CAP.
HOWEVER MLCAPE INCREASES TO NEAR 2000 J/KG AHEAD OF THE FRONT DURING
THE AFTERNOON AND DEEP LAYER SHEAR WILL BETWEEN 30-40KTS, SO IF
CONVECTION CAN DEVELOP THERE WILL BE THE POTENTIAL FOR STRONG TO
SEVERE STORMS. STEEP MID LEVEL LAPSE RATES LEND TO LARGE HAIL BEING
THE PRIMARY THREAT, WITH DAMAGING WIND SECONDARY. THUNDERSTORM
THREAT WILL END WITH THE FROPA, WHICH SHOULD BE THROUGH OUR SOUTH
CENTRAL ILLINOIS COUNTIES BY 00Z WEDNESDAY OR SHORTLY THEREAFTER.
CARNEY
LONG TERM
(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 346 AM CDT MON MAY 19 2025
THE SYSTEM MOVES OVER THE GREAT LAKES BY WEDNESDAY AND RIDGE
BUILDS OVER THE ROCKIES. THIS WILL PRODUCE DEEP NORTHWEST FLOW
OVER THE MID MISSISSIPPI VALLEY FOR WEDNESDAY THROUGH FRIDAY
RESULTING IN RELATIVELY QUIET AND COOL WEATHER. LOWS BOTTOM OUT
IN THE MID 40S ON THURSDAY MORNING, AND HIGHS WILL RUN 10-20
DEGREES BELOW NORMAL THROUGH THE PERIOD, MAINLY IN THE 60S TO NEAR
70. THE NORTHWEST FLOW WILL CARRY A FEW VORTICITY MAXIMA ACROSS
THE THE AREA, SO SOME ISOLATED SHOWERS WILL BE POSSIBLE. ANY RAIN
THAT DEVELOPS SHOULD BE VERY LIGHT AS INSTABILITY WILL BE
INSUFFICIENT FOR DEEP CONVECTION.
NEXT WEEKEND IS BEGINNING TO LOOK MORE ACTIVE, THOUGH THERE'S LITTLE
CONSENSUS IN THE MEDIUM RANGE MODELS. THE GFS SHOWS A SHORT WAVE
MOVING ACROSS THE NORTHERN ROCKIES FRIDAY AND ROUNDING THE TOP OF
THE RIDGE FRIDAY NIGHT/SATURDAY MORNING. THIS FORCES LOW LEVEL
CYCLOGENESIS OVER THE CENTRAL PLAINS AND A 40-60KT LOW LEVEL JET
DEVELOPS BY 06Z SATURDAY ACROSS OKLAHOMA AND KANSAS RESULTING IN
STRONG LOW LEVEL MOISTURE CONVERGENCE AND THE APPARENT DEVELOPMENT
OF AN MCS WHICH MOVES SOUTHEAST FROM NEBRASKA ACROSS MISSOURI INTO
SOUTHWEST ILLINOIS. A LOOK AT THE NBM AND LREF PRECIPITATION
FORECASTS SHOWS MUCH LESS QPF THAN THE DETERMINISTIC GFS, AND THE
HIGHEST AMOUNTS ARE FARTHER TO THE SOUTHWEST ACROSS KANSAS,
OKLAHOMA, AND FAR SOUTHWEST MISSOURI. EVEN THE 75TH PERCENTILE ON
BOTH ENSEMBLES SHOWS LITTLE QPF OVER OUR FORECAST AREA. THE
CONCENTRATED NATURE OF THE MOISTURE CONVERGENCE AND QPF LOOKS VERY
MUCH LIKE GRID-SCALE CONVECTIVE FEEDBACK, SO I DOUBT THE FORECAST
WILL PAN OUT EXACTLY LIKE THE DETERMINISTIC GFS IS DEPICTING.
HOWEVER, THE ENSEMBLES DO SHIFT THE PATTERN SLOWLY EASTWARD OVER THE
WEEKEND SO THERE IS POTENTIAL FOR WARM ADVECTION AND PRECIPITATION.
CARNEY
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1108 PM CDT SUN MAY 18 2025
TRENDS OVER THE LAST SEVERAL HOURS NOT ONLY SHOW A CONTINUED DELAY
IN SHOWERS AND THUNDERSTORMS TONIGHT INTO EARLY MONDAY MORNING. IR
SATELLITE SHOWS COLDER CLOUD TOPS WARMING AS THEY TRACK NORTHEAST
INTO SECTIONS OF CENTRAL AND NORTHERN MISSOURI, INDICATING THAT
THE POTENTIAL FOR STRONGER STORMS IS LESSING WITH EASTWARD TRAVEL.
TERMINALS MAY NOT ENTIRELY AVOID THUNDERSTORMS, BUT TRENDS DO NOT
LOOK SUPPORTIVE FOR SEVERE WEATHER TONIGHT INTO EARLY MONDAY. THE
MAIN QUESTION THEN WILL BE WHETHER MVFR CLOUD COVER MATERIALIZES
AND TO WHAT EXTENT AND DURATION. IT'S MORE LIKELY THAT MVFR TRACKS
ALONG AND AHEAD OF THE WARM FRONT AS IT LIFTS NORTHWARD WITH
WEAKENING ACTIVITY, THEN BEGINS TO LIFT AND SCATTER BACK TO VFR
MONDAY LATE MORNING INTO THE AFTERNOON.
WITH THE INITIAL ROUND OF CONVECTION WEAKENING TONIGHT, THIS LEADS
TO CONCERNS FOR MONDAY AFTERNOON AND EVENING. SHOULD TONIGHT'S
TRENDS CONTINUE, THE LACK OF COVERAGE AND PRECIPITATION WOULD
ALLOW FOR QUICKER RECOVERY OF INSTABILITY WITHIN THE WARM SECTOR
MONDAY. YET ANOTHER DISTURBANCE APPROACHES LATE MONDAY AFTERNOON,
POTENTIALLY TAPPING INTO BETTER INSTABILITY AND RESULTING IN
STRONG TO SEVERE THUNDERSTORM DEVELOP OVER THE EAST PLAINS INTO
WESTERN MISSOURI. THIS ACTIVITY WOULD THEN MOVE INTO CENTRAL MO BY
LATE AFTERNOON/EVENING, CONTINUING EAST INTO THE LATE EVENING.
GIVEN THE UNCERTAINTY IN THE EVOLUTION OF THIS SYSTEM, TAFS
COVERED THE POTENTIAL WITH SHRA, LEAVING ROOM FOR BETTER DETAIL
AND TIMING FOR TSRA POTENTIAL LATE IN THE PERIOD. THUNDERSTORMS
WILL LIKELY RESULT IN MVFR/IFR CONDITIONS FOR TERMINALS TAKING
DIRECT IMPACT WITH LOCALIZE LIFR CONDITIONS IN STRONGER STORMS.
MAPLES
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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