486
FXUS63 KLSX 181938
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
238 PM CDT SUN MAY 18 2025
KEY MESSAGES
- THERE IS A LIMITED THREAT FOR STRONG TO SEVERE THUNDERSTORM
CHANCES TONIGHT, WITH THE BEST CHANCE ACROSS CENTRAL MISSOURI.
- THERE IS A MORE WIDESPREAD THREAT FOR SEVERE THUNDERSTORMS
MONDAY AFTERNOON AND EVENING WITH ALL HAZARDS POSSIBLE. LOCALLY
HEAVY RAINFALL IS ALSO POSSIBLE.
SHORT TERM
(THROUGH TUESDAY NIGHT)
ISSUED AT 237 PM CDT SUN MAY 18 2025
(TONIGHT INTO MONDAY MORNING)
OUR BRIEF PERIOD OF CALM IS COMING TO AN END. CONVECTION WILL KICK
OFF ACROSS KANSAS AND OKLAHOMA THIS AFTERNOON AND ORGANIZE INTO AN
MCS THAT WILL TRACK EAST ALONG A WARM FRONT. MOST DETERMINISTIC
GUIDANCE IS PLACING THE WARM FRONT ACROSS SOUTHERN MISSOURI INTO FAR
SOUTHERN ILLINOIS, WHICH WOULD BRING THE MCS THROUGH MAINLY ALONG
AND SOUTH OF I-70. HI-RES GUIDANCE HAS STARTED TO SLOW THE ONSET AND
ENDING OF THE MCS ACROSS OUR AREA, BRINGING IT INTO CENTRAL MISSOURI
AFTER MIDNIGHT AND INTO THE ST. LOUIS METRO DURING THE EARLY MORNING
HOURS NEAR SUNRISE. THUNDERSTORMS ARE EXPECTED TO BE EMBEDDED WITHIN
THE LARGER MCS, BUT HOW MANY AND HOW STRONG THEY GET REMAINS
UNCERTAIN. THE DOWNWARD TREND IN INSTABILITY HAS CONTINUED FROM LAST
NIGHT, WITH HREF GUIDANCE SHOWING 500 J/KG OF MUCAPE OR LESS ACROSS
OUR AREA OVERNIGHT, LIMITING THE STRENGTH AND COVERAGE OF THE STORMS
WITHIN THE MCS. 0-6 KM SHEAR REMAINS SUFFICIENT (40-50KTS), HOWEVER,
AND IF A THUNDERSTORM IS ABLE TO PRODUCE A ROBUST UPDRAFT, THE SHEAR
WILL BE ABLE TO ORGANIZE AND MAINTAIN IT. ANY STORMS THAT BECOME
STRONG TO SEVERE WILL BE CAPABLE MAINLY OF LARGE HAIL AND DAMAGING
WINDS. THE BEST LOCATION FOR STRONG TO SEVERE THUNDERSTORMS WILL BE
ACROSS CENTRAL MISSOURI WHERE INSTABILITY WILL BE MAXIMIZED.
THE WEAKENING INSTABILITY WILL ALSO LEND TO A DECREASING FLOOD
THREAT OVERNIGHT. WHILE THE SOUTHWARD SHIFT IN THE TRACK OF THE MCS
MOVES THE RAIN INTO A MORE SATURATED ENVIRONMENT, THE PROBABILITY
MATCHED MEAN QPF FROM THE HREF INDICATE UP TO 1.25" OVER 3 HOURS IS
THE MAXIMUM RAINFALL EXPECTED FROM THIS SYSTEM. WHILE NUISANCE
PONDING MAY DEVELOP UNDER HEAVIER THUNDERSTORMS, THE THREAT
FOR MORE SIGNIFICANT IMPACTS REMAINS LOW.
THERE IS A 40-50% CHANCE THAT ANOTHER ROUND OF SHOWERS AND A FEW
THUNDERSTORMS DEVELOPS ALONG THE NOSE OF THE LOW-LEVEL JET IN
NORTHWEST MISSOURI AND TRACKS EAST THROUGH NORTHERN MISSOURI AND
WEST-CENTRAL ILLINOIS DURING THE MORNING ON THE HEELS OF THE MCS.
NOT ALL GUIDANCE SOURCES DEPICT THIS FEATURE, THUS CONFIDENCE
REMAINS LOW IN WHETHER THIS WILL OCCUR.
(MONDAY AFTERNOON AND EVENING)
TWO SCENARIOS EXIST FOR MONDAY AFTERNOON AND EVENING, HINGING ON THE
EXISTENCE (OR LACK THEREOF) OF THE SECOND ROUND OF MORNING
PRECIPITATION DESCRIBED ABOVE.
1. SECOND ROUND EXISTS, LEADS TO LIMITED AFTERNOON THREAT: IF THE
SECOND ROUND OF SHOWERS AND THUNDERSTORMS EXISTS IT WILL REINFORCE
THE STABLE AND COOL REGION NORTH OF THE WARM FRONT. THIS AND THE
ADDITION OF AN OUTFLOW BOUNDARY WILL LIMIT THE NORTHWARD MOTION OF
THE WARM FRONT DURING THE DAY. AS A RESULT, THUNDERSTORM
DEVELOPMENT DURING THE AFTERNOON WILL BE STUNTED UNTIL A QLCS THAT
DEVELOPS ACROSS EASTERN KANSAS PUSHES EASTWARD THROUGH THE AREA
DURING THE EVENING.
2. ONLY THE FIRST ROUND EXISTS, AFTERNOON THREAT INCREASES: IF THE
SECOND ROUND OF SHOWERS AND THUNDERSTORMS DOESN'T MATERIALIZE
ACROSS NORTHERN MISSOURI AND WEST-CENTRAL ILLINOIS, THE WARM FRONT
WILL ADVANCE NORTHWARD THROUGH OUR AREA MORE EFFECTIVELY. THIS
WOULD LEAD TO A GREATER PORTION OF THE FORECAST AREA WITHIN THE
WARM SECTOR, WITH ACCESS TO 1500-2500 J/KG OF SURFACE BASED CAPE,
30-45 KTS OF 0-6 KM SHEAR, AND 20 KTS OF SOUTHERLY (IE BACKED) 0-1
KM SHEAR. IN THIS SCENARIO ISOLATED TO SCATTERED AFTERNOON
CONVECTION WITHIN THE WARM SECTOR IS EXPECTED, LEADING TO AN
INCREASED HAIL AND TORNADO THREAT. WHILE THE HAIL THREAT HAS
DECREASED SOMEWHAT SINCE YESTERDAY GIVEN THE LOWER CAPE VALUES AND
SKINNIER SOUNDINGS, IT IS STILL A FAVORABLE ENVIRONMENT FOR LARGE
HAIL. THE BACKED 0-1 KM SHEAR, MODEST INSTABILITY, LOW LCLS, AND
CURVED HODOGRAPHS ALL SUPPORT AN ENVIRONMENT CAPABLE OF STRONG
TORNADOES, PARTICULARLY ACROSS WESTERN MISSOURI AND INTO PORTIONS
OF CENTRAL MISSOURI.
REGARDLESS OF HOW THE AFTERNOON PLAYS OUT, CONVECTION WILL FIRE
ACROSS EASTERN KANSAS AND FORM IN A QLCS THAT MARCHES ACROSS
MISSOURI DURING THE AFTERNOON AND EARLY EVENING HOURS, ENTERING
ILLINOIS BY THE LATE EVENING. DAMAGING WINDS AND SHORT-LIVED
TORNADOS ARE THE MAIN CONCERNS WITH THIS SYSTEM, PARTICULARLY
CONSIDERING THE 30-40KTS OF 0-3 KM SHEAR NEARLY LINE NORMAL SHEAR.
MORE SIGNIFICANT RAINFALL IS EXPECTED WITH THE QLCS AS IT MOVES
ACROSS THE FORECAST AREA. HREF PROBABILITY MATCHED MEAN GUIDANCE
INDICATES THE POTENTIAL FOR 2-2.5 INCHES IN 3 HOURS ALONG PORTIONS
OF THE LINE, WITH UP TO 3-4 INCHES IN 3 HOURS WHERE THUNDERSTORMS
TRAIN. THIS WOULD RESULT IN MORE WIDESPREAD FLOODING OF ROADWAYS AND
SMALL CREEKS AND STREAMS. CONFIDENCE IN THIS OCCURRING OR WHERE IT
WOULD OCCUR IS LOW GIVEN THE UNCERTAINTY IN THE DISTRIBUTION AND
MOVEMENT OF CONVECTIVE ELEMENTS. THIS WILL BE A MESSY EVENT TO SAY
THE LEAST.
(TUESDAY)
TURNING TO TUESDAY, WHILE CONVECTION MAY BE ONGOING EARLY TUESDAY
MORNING ACROSS THE FORECAST AREA, INSTABILITY IS EXPECTED TO BE AT A
PREMIUM (<500 J/KG MUCAPE) AND IF THUNDERSTORMS ARE PRESENT THEY
AREN'T EXPECTED TO BE STRONG. A COLD FRONT WILL MOVE THROUGH THE
AREA DURING THE MORNING TO EARLY AFTERNOON, BRINGING ANOTHER SHOT OF
SHOWERS AND A FEW THUNDERSTORMS TO THE REGION. CONFIDENCE IN STRONG
TO SEVERE THUNDERSTORMS IS LOW DUE TO THE VERY POOR MOISTURE
CONVERGENCE ALONG THE FRONT AND WEAK INSTABILITY, AND WE ARE NOT
CURRENTLY MESSAGING THE DAY 3 SLIGHT RISK. THE SYSTEM WILL BE
OCCLUDED AS IT ROLLS THROUGH, AND SO AN ADDITIONAL SHOT OF SHOWERS
LATER IN THE DAY TUESDAY TO TUESDAY EVENING IS POSSIBLE AS THE
SYSTEM EXITS EASTWARD.
DELIA
LONG TERM
(WEDNESDAY THROUGH NEXT SUNDAY)
ISSUED AT 237 PM CDT SUN MAY 18 2025
BEHIND TUESDAY'S COLD FRONT CONDITIONS WILL BE COOLER, WITH NBM
INTERQUARTILE HIGH TEMPERATURES BELOW NORMAL THROUGH NEXT WEEKEND.
MULTIPLE CHANCES FOR SHOWERS AND THUNDERSTORMS EXIST DURING THIS
PERIOD AS WELL WITH NO ONE PERIOD DOMINATING THE CHANCES.
DELIA
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1231 PM CDT SUN MAY 18 2025
DRY AND VFR CONDITIONS WILL CONTINUE INTO THIS EVENING AHEAD OF
THE NEXT WEATHER SYSTEM THAT WILL MOVE INTO CENTRAL MISSOURI
OVERNIGHT, BRINGING SHOWERS AND THUNDERSTORMS TO THE MID-MISSOURI
TERMINALS. THE SYSTEM WILL PROGRESS EAST THROUGH THE EARLY MORNING
HOURS, IMPACTING THE ST. LOUIS METRO TERMINALS BEFORE SUNRISE.
THERE HAS BEEN A TREND TOWARDS A SLOWER ENTRANCE AND EXIT OF THIS
PRECIPITATION, BUT CONFIDENCE IN THIS IS LOW SO I'VE KEPT THE
TIMING OF THE THUNDERSTORMS AS IT FOR NOW.
MVFR CEILINGS ARE EXPECTED WITH THESE THUNDERSTORMS, AND WILL
LINGER BEHIND THE SYSTEM AS WELL. INCREASED HEATING THROUGH THE
MORNING WILL HELP THE LINGERING DECK TO LIFT AND SCATTER BY THE
AFTERNOON HOURS. ANOTHER ROUND OF THUNDERSTORMS IS EXPECTED MONDAY
AFTERNOON AND EVENING, ALTHOUGH CONFIDENCE IN WHEN AND WHERE THESE
STORMS OCCUR IS TOO LOW TO MENTION IN THE TAFS AT THIS POINT.
WINDS ARE CURRENTLY NORTHERLY TO EASTERLY, THOUGH LIGHT AND SO
COULD CHANGE DIRECTION EASILY THIS AFTERNOON. WINDS WILL BECOME
SOUTHEASTERLY AND REMAIN THERE, INCREASING IN SPEED TOMORROW
AFTERNOON.
DELIA
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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