203
FXUS63 KLSX 250642
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
142 AM CDT THU JUN 25 2026
KEY MESSAGES
- SHOWERS AND THUNDERSTORMS CAPABLE OF HEAVY RAINFALL ARE
EXPECTED THIS AFTERNOON INTO TOMORROW MORNING. A FLASH FLOOD
WATCH REMAINS IN EFFECT FOR MUCH OF THE AREA.
- A FEW THUNDERSTORMS THIS AFTERNOON MAY BECOME STRONG ENOUGH TO
PRODUCE DAMAGING WINDS.
- POTENTIALLY DANGEROUS HEAT AND HUMIDITY WILL BUILD INTO THE
REGION STARTING SUNDAY AND CONTINUE THROUGH NEXT WEEK.
SHORT TERM /THROUGH SATURDAY/
ISSUED AT 126 AM CDT THU JUN 25 2026
A WEAK COLD FRONT HAS DROPPED INTO THE MID MISSISSIPPI VALLEY
AND WILL SLOWLY OOZE SOUTH TODAY BENEATH QUASI-ZONAL FLOW ALOFT.
MOST OF THE CAMS BELIEVE THAT THIS FRONT WILL CONTINUE TO PROVIDE
ENOUGH FORCING TO SQUEEZE OUT ISOLATED TO WIDELY SCATTERED
THUNDERSTORMS. WITH AN ATMOSPHERE CHARACTERIZED BY 1000-2000
J/KG OF MLCAPE AND 25-35 KTS OF DEEP LAYER WIND SHEAR, A FEW OF
THESE STORMS MAY BECOME ORGANIZED ENOUGH TO PRODUCE DAMAGING
WINDS.
THIS EVENING AND OVERNIGHT, A SHORTWAVE CURRENTLY OVER THE
INTERMOUNTAIN WEST WILL APPROACH THE REGION. THIS DISTURBANCE
WILL SPUR LOW LEVEL CYCLOGENESIS OVER THE CENTRAL PLAINS, WHICH
IN TURN WILL ESTABLISH A LOW LEVEL JET FROM EASTERN TEXAS
THROUGH MISSOURI. THE RESULTANT DEEP MOIST CONVECTION AT THE
INTERFACE OF THE LOW LEVEL JET AND THE STALLED FRONT WILL
INITIATE WIDESPREAD CONVECTION ALONG THE FRONT. GIVEN
PRECIPITABLE WATER APPROACHING 2", WARM CLOUD DEPTHS AROUND
10,000', MODEST INSTABILITY AND WIND SHEAR, AND THE POTENTIAL
FOR TRAINING STORMS ALONG THE FRONT, THIS IS A CLASSIC SETUP
FOR VERY HEAVY RAINFALL AND FLASH FLOODING.
INDEED, BOTH THE 18Z REFS AND 00Z HREF LPMM SHOW A STRIPE OF
3-5" OF QPF ACROSS THE SOUTHERN HALF OF MISSOURI, THOUGH BOTH
MODELS HAVE PUSHED THE HEAVY RAIN A BIT FURTHER SOUTH THAN
PREVIOUS RUNS. I SUSPECT THE FORECAST FOR THE HEAVIEST RAIN WILL
CONTINUE TO WAVER SOMEWHAT DUE TO THE LOW PREDICTABILITY OF THE
FRONTAL POSITIONING. WHEREVER THE HEAVY RAIN DOES FALL, IT WILL
BE ENOUGH TO GENERATE AT LEAST ISOLATED FLASH FLOODING. IF THE
RAIN OVERACHIEVES, OR IF IT IMPACTS AN AREAS SUSCEPTIBLE TO
FLASH FLOODING (URBAN/SUBURBAN AREAS), THE FLOODING COULD BE
MORE WIDESPREAD OR IMPACTFUL.
AFTER SUNRISE ON FRIDAY MORNING, THE SHORTWAVE WILL DEPART TO THE
EAST AND THE LOW LEVEL JET WILL DISSIPATE, RESULTING IN A RAPID
DECREASE IN THUNDERSTORM COVERAGE. NEVERTHELESS, THE STALLED FRONT
WILL REMAIN ACROSS THE REGION AND SEVERAL OF THE ABOVE FACTORS
SUPPORTIVE OF HEAVY RAINFALL WILL STILL BE IN PLACE. SO WHILE
THUNDERSTORM COVERAGE IS EXPECTED TO BE LESS ON FRIDAY, THE THREAT
FOR FLASH FLOODING MAY EXTEND INTO AT LEAST THE AFTERNOON. AN
EXTENSION OF THE WATCH MAY BE NEEDED ONCE MODELS COME INTO BETTER
CONSENSUS ON WHERE THIS ADDITIONAL CONVECTION WILL OCCUR.
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
ISSUED AT 126 AM CDT THU JUN 25 2026
UPPER LEVEL RIDGING WILL BEGIN TO BUILD INTO THE REGION ON FRIDAY,
AND WILL CONTINUE TO AMPLIFY THROUGH THE WEEKEND. THIS HELP PUSH THE
ABOVE FRONT TO THE NORTH THROUGH THE REGION, WHICH MAY RESULT IN ONE
MORE ROUND OF CONVECTION ON SATURDAY BEFORE DEPARTING THE MID
MISSISSIPPI VALLEY. BEHIND THE FRONT, DEEP, PERSISTENT WARM AIR
ADVECTION WILL PUSH 850MB TEMPS INTO THE MID 20S C BENEATH 500MB
HEIGHTS IN EXCESS OF 590 DAM. THESE VALUES ARE TYPICALLY ASSOCIATED
WITH HEAT WAVES, AND THE LATEST GUIDANCE IS INDEED COMING IN QUITE
HOT FROM SUNDAY THROUGH THE MIDDLE OF NEXT WEEK. MODEL GUIDANCE
IS CONSPICUOUSLY DEVOID OF THROUGH MUCH OF THAT PERIOD,
INCREASING CONFIDENCE THAT WE WILL SEE OUT FIRST SIGNIFICANT
HEAT EPISODE OF THE YEAR.
AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 1227 AM CDT THU JUN 25 2026
THERE WILL BE MULTIPLE ROUNDS OF THUNDERSTORMS THROUGHOUT THE
TAF PERIOD ASSOCIATED WITH A COLD FRONT SAGGING THROUGH THE
REGION. THIS FIRST ROUND HAS ALREADY STARTED WITH
ISOLATED/SCATTERED STORMS IN THE VICINITY OF KUIN. THESE STORMS
WILL PERSIST ON AND OFF THROUGH THE DAY AS THE FRONT OOZES TO
THE SOUTH, AND SHOULD BE NEAR ALL OF THE OTHER TERMINALS BY THE
LATE MORNING OR AFTERNOON. I'VE ADDED A PROB30 GROUP FOR THOSE
TAFS WHEN I THINK THE STORMS ARE THE MOST LIKELY, BUT THEY ARE
POSSIBLE PRETTY MUCH AT ANY POINT THROUGH THE DAY.
MORE WIDESPREAD THUNDERSTORMS ARE EXPECTED TO DEVELOP SOMETIME THIS
EVENING AND SHOULD PERSIST THROUGH MUCH OF THE NIGHT. AGAIN,
IT'S DIFFICULT TO PINPOINT EXACTLY WHEN THE STORMS WILL IMPACT
EACH TERMINAL, BUT I'VE INCLUDED A PERIOD OF PREVAILING
THUNDERSTORMS WHEN THEY APPEAR TO BE THE MOST LIKELY. THE
EXCEPTION TO THIS IS AT KCPS AND KSUS WHERE I EXPECT THE MOST
WIDESPREAD STORMS TO HOLD OFF UNTIL AFTER 06Z.
THE OTHER CONCERN IS THE POTENTIAL FOR MVFR CIGS WITH THE ONSET
OF THE MORE WIDESPREAD STORMS. I'VE KEPT THIS OUT OF THE TAFS
FOR NOW, BUT MAY NEED TO BE INCLUDED IN SUBSEQUENT FORECASTS.
LSX WATCHES/WARNINGS/ADVISORIES
MO...FLOOD WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH FRIDAY
MORNING FOR MOZ036-041-042-047>052-059>065-072>075-084-
085-099.
IL...FLOOD WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH FRIDAY
MORNING FOR ILZ058>060-064-065-069-070-074-079-097>102.
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...BSH
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