827
FXUS63 KLSX 170539
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
1239 AM CDT FRI APR 17 2026
KEY MESSAGES
- THE THREAT OF ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS
WILL CONTINUE ACROSS SOUTHEASTERN MISSOURI THROUGH EARLY THIS
EVENING. A STORM OR TWO WILL BE CAPABLE OF PRIMARILY LARGE HAIL.
- WIDESPREAD THUNDERSTORMS ARE EXPECTED FRIDAY AFTERNOON AND EVENING
ALONG A COLD FRONT. SEVERAL THUNDERSTORMS WILL BE CAPABLE OF
DAMAGING WIND GUSTS, WITH LARGE HAIL AND TORNADOES BEING
SECONDARY THREATS.
SHORT TERM
(THROUGH LATE FRIDAY NIGHT)
ISSUED AT 217 PM CDT THU APR 16 2026
THUNDERSTORMS HAVE FORMED ACROSS SOUTHEASTERN MISSOURI THIS
AFTERNOON ROUGHLY AT THE NOSE OF A WING OF WARM AIR ADVECTION.
SUBTLE FORCING FROM THIS ADVECTION PAIRED WITH LIFT FROM THE AXIS OF
A WEAK SHORTWAVE ALOFT WILL LEAD TO A LOW THREAT (20-40% CHANCE) FOR
SHOWERS AND THUNDERSTORMS CENTERED ON SOUTHEASTERN MISSOURI THROUGH
EARLY THIS EVENING. INSTABILITY IN THIS PART OF THE AREA CONTINUES
TO BUILD, WITH SPC MESOANALYSIS SHOWING 2,000-2,500 J/KG OF MLCAPE
PRESENT ALONG AND SOUTH OF I-70. CONTINUING WARM AIR ADVECTION
THROUGH THIS EVENING WILL SUSTAIN THIS INSTABILITY AND ADVECT IT
SLIGHTLY EAST-NORTHEASTWARD THROUGH THIS EVENING. DEEP-LAYER SHEAR
IS PROGGED TO REMAIN AROUND 30 KTS, FAVORING MULTICELLS WITH BRIEF
SUPERCELLULAR STRUCTURES. THIS ENVIRONMENT FAVORS LARGE HAIL AS THE
PRIMARY THREAT, WITH DCAPE RIGHT AROUND 1,000 J/KG LEADING TO
DAMAGING WIND GUSTS BEING A SECONDARY THREAT. WEAK LOW-LEVEL SHEAR
AND MEAGER SRH ARE EXPECTED TO MITIGATE A THREAT OF TORNADOES.
WEAKENING LAPSE RATES AND A STRENGTHENING CAP LATER THIS EVENING (8-
9PM) WILL END THE THREAT OF CONVECTION.
TOMORROW, AN UPPER-LEVEL TROUGH WILL EJECT OUT INTO THE GREAT
PLAINS, ENHANCING SOUTHWESTERLY FLOW OVER THE MIDDLE MISSISSIPPI
VALLEY. AT THE SURFACE, A LOW WILL DEEPEN OVER THE CENTRAL PLAINS
AND MOVE INTO THE UPPER MIDWEST, SWEEPING A COLD FRONT ACROSS THE
PLAINS AND MIDWEST. AHEAD OF THIS FRONT DURING THE AFTERNOON OVER
THE MIDDLE MISSISSIPPI VALLEY, GUIDANCE CONTINUES TO POINT TO A VERY
UNSTABLE AIRMASS CHARACTERIZED BY 3,000-4,000 J/KG OF SBCAPE. THE
APPROACHING TROUGH AND A LOW-LEVEL JET RAMPING UP OVER THE REGION
WILL INCREASE DEEP-LAYER SHEAR THROUGH THE DAY, WITH GENERALLY 30-40
KTS FORECAST AMONG HI-RES GUIDANCE.
WHILE MODEL SOUNDINGS SHOW CAPPING THROUGH MUCH OF THE AFTERNOON,
THE APPROACHING FRONT PAIRED WITH LIFT VIA A LEADING SHORTWAVE AND
JET STREAK COUPLING WILL SPAWN UPDRAFTS ACROSS WESTERN AND NORTHERN
MISSOURI DURING THE MID TO LATE AFTERNOON ALONG AND AHEAD OF THE
FRONT. GIVEN THE AMOUNT OF SHEAR AND INSTABILITY, A MULTICELLULAR
AND SUPERCELLULAR STORM MODES ARE ANTICIPATED. THE DEGREE OF FORCING
WILL LEAD TO NUMEROUS UPDRAFTS FORMING IN CLOSE PROXIMITY, FAVORING
STORM INTERACTION AND UPSCALE GROWTH INTO A CONVECTIVE LINE QUICKLY.
WHILE STORMS ARE DISCRETE, THE LARGE HAIL THREAT WILL BE GREATEST,
WITH THE STRONGEST UPDRAFTS CAPABLE OF HAIL UP TO AROUND 2.5" IN
DIAMETER. RELATIVE TO OUR CWA, THIS THREAT IS GREATEST ACROSS FAR
NORTHEASTERN MISSOURI WHERE A MINORITY OF GUIDANCE PRODUCES DISCRETE
CONVECTION PRIOR TO UPSCALE GROWTH.
CONFIDENCE IS HIGH THAT STORMS WILL GROW UPSCALE INTO A SQUALL LINE
PRIOR TO ENTERING THE REST OF THE CWA. STEEP LOW-LEVEL LAPSE RATES
FAVOR A DAMAGING WIND THREAT WITH BOTH DISCRETE STORMS AND BOWING
SEGMENTS WITHIN THE SQUALL LINE. WITH GUIDANCE CONSENSUS FAVORING 20-
25 KTS OF 0-1 KM SHEAR AND A LITTLE OVER 150 M2/S2 OF SRH WITHIN THE
SAME LAYER, THERE IS A LOW TORNADO THREAT WITH EITHER STORM MODE.
BULK 0-3 KM SHEAR OF 30-35 KTS WILL FAVOR MESOVORTEX DEVELOPMENT
WITHIN THE SQUALL LINE, THOUGH GUIDANCE DIFFERS ON THE ORIENTATION
OF THE VECTOR. A MORE WEST-EAST ORIENTATION WOULD FAVOR A GREATER
QLCS TORNADO THREAT, WHILE A SOUTHWEST-NORTHEAST ORIENTATION LIMITS
THE THREAT TO THE NORTHERN PERIPHERY OF BOWING SEGMENTS.
THE THREATS ARE EXPECTED TO PEAK LATE AFTERNOON INTO THE EARLY
EVENING ACROSS CENTRAL AND NORTHEASTERN MISSOURI. AS THE LINE MOVES
FURTHER EASTWARD, DIMINISHING INSTABILITY WILL LEAD TO A WEAKENING
TREND DURING THE LATE EVENING AND OVERNIGHT HOURS. THE AFOREMENTIONED
ROBUST FORCING WILL CONTINUE OVERNIGHT, LEADING TO AN EXPANSIVE AREA
OF STRATIFORM RAINFALL THAT WILL CONTINUE THROUGH EARLY SATURDAY
MORNING.
ELMORE
LONG TERM
(SATURDAY THROUGH NEXT THURSDAY)
ISSUED AT 217 PM CDT THU APR 16 2026
EARLY SATURDAY, THE AFOREMENTIONED TROUGH WILL CONTINUE TO EDGE
EASTWARD THROUGH THE MIDWEST PER GUIDANCE CONSENSUS, PUSHING
FRIDAY'S FRONT DEEPER INTO THE OHIO VALLEY. WITH UPPER-LEVEL FLOW
NOT BECOMING NORTHWESTERLY UNTIL SUNDAY AND THE CORE OF THE POST-
FRONTAL AIRMASS REMAINING NORTH OF THE CWA, WE WILL MISS OUT ON THE
COLDEST TEMPERATURES. HOWEVER, THE MAJORITY OF ENSEMBLE GUIDANCE
FAVORS VALUES BELOW CLIMATOLOGY THROUGH THE WEEKEND, WITH A LOW
CHANCE FOR FROST FOR PORTIONS OF THE AREA SATURDAY NIGHT AND SUNDAY
MORNING.
RIDGING QUICKLY BUILDS INTO THE REGION MONDAY PER BOTH ENSEMBLE
CLUSTERS AND DETERMINISTIC MODELS, WITH SOUTHWESTERLY LOW-LEVEL FLOW
RETURNING TO THE MIDDLE MISSISSIPPI VALLEY. GUIDANCE SUPPORTS THIS
PATTERN CONTINUING THROUGH MIDWEEK, CORRESPONDING WITH TEMPERATURES
GRADUALLY WARMING TO AND THEN ABOVE NORMAL BY WEDNESDAY-THURSDAY.
ELMORE
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1232 AM CDT FRI APR 17 2026
THE PRIMARY CONCERN WITH THIS TAF PERIOD IS THE ARRIVAL OF
THUNDERSTORMS LATE TOMORROW AFTERNOON THROUGH TOMORROW EVENING
AND OVERNIGHT. DRY VFR CONDITIONS ARE EXPECTED TONIGHT THROUGH
MOST OF TOMORROW AFTERNOON, ALBEIT WITH GUSTY SOUTH WINDS
DEVELOPING BY LATE MORNING. A FEW SCATTERED SHOWERS AND STORMS MAY
DEVELOP BY MID AFTERNOON, MAINLY AT COU/JEF, CONFIDENCE IS LOWER
THAT THIS EARLY DEVELOPMENT WILL MATERIALIZE. HOWEVER, HIGH
CONFIDENCE EXISTS THAT A LINE OF THUNDERSTORMS WILL IMPACT ALL
TERMINALS LATE IN THE PERIOD, FIRST AT UIN/COU/JEF LATE AFTERNOON
THROUGH THE EVENING. STORMS DURING THIS PERIOD MAY PRODUCE VERY
STRONG WIND GUSTS, HEAVY RAIN AND FREQUENT LIGHTNING, WITH A LOWER
PROBABILITY OF LARGE HAIL AND A TORNADO.
THIS LINE IS EXPECTED TO WEAKEN AS IT MOVES FURTHER EAST, BUT AT A
MINIMUM ST. LOUIS AREA TERMINALS WILL BE IMPACTED BY A PERIOD OF
STEADY RAIN WITH AT LEAST A REASONABLE POTENTIAL FOR LIGHTNING AND
BURSTS OF HEAVIER RAIN AND/OR GUSTY AND ERRATIC WINDS VERY LATE IN
THE EVENING AND OVERNIGHT.
FINALLY, A COLD FRONT WILL SWITCH WINDS TO THE NORTHWEST AS STORMS
END, AND POTENTIALLY BRINGING A PERIOD OF LOWER CEILINGS TO MVFR
LEVELS, OR PERHAPS BRIEFLY LOWER.
BRC
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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