521
FXUS63 KLSX 171040
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
440 AM CST TUE DEC 17 2024
KEY MESSAGES
- THERE WILL BE CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS
TONIGHT WITH THE BEST CHANCE (50-70%) OVER SOUTHEAST MISSOURI
INTO SOUTHWEST ILLINOIS.
- TEMPERATURES WILL TREND COOLER THROUGH THE END OF THE WEEK.
SHORT TERM
(THROUGH LATE WEDNESDAY AFTERNOON)
ISSUED AT 335 AM CST TUE DEC 17 2024
THE LATEST SURFACE ANALYSIS IS SHOWING HIGH PRESSURE CENTERED OVER
WESTERN MISSOURI WITH A COLD FRONT EXTENDING FROM THE WESTERN GREAT
LAKES ACROSS IOWA INTO THE NORTHERN PLAINS. MOST OF THE AREA WAS
CLEAR, THOUGH HIGH CLOUDS ARE BEGINNING TO STREAM INTO THE NORTHWEST
MISSOURI AHEAD OF AN UPPER TROUGH CURRENTLY OVER THE NORTHERN
ROCKIES. THE HREF HAS THE UPPER TROUGH MOVING TOWARD THE AREA LATER
TODAY AND THIS EVENING WITH A 35 KNOT LOW LEVEL JET PICKING UP OUT
OF THE SOUTHWEST BY LATE THIS EVENING. THE COMBINATION OF ASCENT
AND LOW LEVEL MOISTURE CONVERGENCE WILL GENERATE SCATTERED SHOWERS
ACROSS THE AREA BEGINNING THIS EVENING THAT WILL CONTINUE INTO THE
OVERNIGHT HOURS WITH THE HIGHEST CHANCES (50-70%) OVER SOUTHEAST
MISSOURI INTO SOUTHWEST ILLINOIS. THERE WILL ALSO BE SLIGHT CHANCE
FOR THUNDERSTORMS TONIGHT OVER SOUTHEAST MISSOURI AS THE NAM/ECMWF
ARE BOTH SHOWING SMALL AMOUNTS OF MUCAPE (<500 J/KG). THIS SYSTEM
WILL HAVE LESS MOISTURE TO WORK WITH THAN SUNDAY NIGHT'S SYSTEM WITH
PWATS ONLY IN THE 0.6-0.8" RANGE WHICH IS REFLECTED BY BOTH THE
LOWER POPS AND FORECAST QFP AMOUNTS. BOTH THE NBM AND THE HREF LPMM
ARE ONLY SHOWING QFP AMOUNTS OF UNDER A TENTH OF A INCH. SNOW
CHANCES OVER THE NORTH LOOK DOUBTFUL AS THE PRECIPITATION WILL BE
MOVING OUT OVER NORTHEAST MISSOURI AND WEST CENTRAL BEFORE IT WILL
BE COLD ENOUGH FOR A CHANGEOVER. NONE OF THE HREF MEMBER ARE
SHOWING ANY SNOW AT UIN OR IRK. WEDNESDAY WILL BE DRY AS SUBSIDENCE
SETS IN THE WAKE OF THE EXITING TROUGH.
THE SURFACE HIGH WILL MOVE OFF THE THE EAST CAUSING WINDS TO TURN
OUT OF THE SOUTHEAST TODAY. HIGHS TODAY WILL NOT BE AS WARM AS
THEY WERE YESTERDAY, BUT WILL STILL BE MAINLY IN THE 50S. LOW
PRESSURE WILL MOVE ACROSS THE AREA TONIGHT AND WILL BRING THE FRONT
THROUGH THE AREA. HIGHS WILL BE 5 TO 10 DEGREES COOLER ON WEDNESDAY
WITH COLD AIR ADVECTION BEHIND THE FRONT.
BRITT
LONG TERM
(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 335 AM CST TUE DEC 17 2024
THE NEXT TROUGH WILL MOVE ACROSS THE UPPER MIDWEST INTO THE GREAT
LAKES THURSDAY AND THURSDAY NIGHT. AVAILABLE MODEL GUIDANCE REMAINS
CONSISTENT WITH KEEPING THE CWA DRY WITH LESS THAN 10% OF THE LREF
MEMBERS SHOWING ANY PRECIPITATION WITH THIS SYSTEM. ANOTHER TROUGH
WILL MOVE THROUGH THE MIDWEST ON SATURDAY, BUT THE DETERMINISTIC
GUIDANCE IS NOT PRODUCING ANY QPF IN THE CWA AND ONCE AGAIN, MOST OF
THE LREF MEMBERS KEEP THE CWA DRY. IT IS NOT UNTIL NEXT WEEK THAT
THE UPPER FLOW BECOMES QUASI-ZONAL AND TROUGH ENTERS THE MIDWEST
THAT WE WILL HAVE A CHANCE FOR PRECIPITATION BY MONDAY. THE LREF
AND THE NBM DOES SUPPORT SOME SNOW MIXING IN WITH THE RAIN ON MONDAY
MORNING, BUT THE QPF AMOUNTS ARE LIGHT WITH THIS SYSTEM.
HIGHS ON WEDNESDAY WILL MAINLY BE IN THE 40S. THE TROUGH ON
THURSDAY NIGHT WILL BRING A FRONT ON THURSDAY NIGHT WILL BRING EVEN
COLDER AIR INTO THE REGION WITH HIGHS FRIDAY AND SATURDAY MAINLY IN
THE 30S. THERE WILL BE SOME MODERATION IN TEMPERATURES BY SUNDAY
INTO MONDAY AS THE SURFACE FLOW TURNS BACK OUT OF THE SOUTHWEST AND
HIGHS CLIMB BACK INTO THE 40S.
BRITT
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 433 AM CST TUE DEC 17 2024
DRY AND VFR CONDITIONS ARE EXPECTED THROUGH 00Z. THEN MVFR
CEILINGS WILL MOVE INTO THE CENTRAL MISSOURI AND ST. LOUIS AREA
AIRPORTS WITH CEILINGS BETWEEN 2000-3000 FEET AGL. THERE WILL ALSO
BE SCATTERED SHOWERS DEVELOPING ACROSS THE AREA AFFECTING UIN AND
THE ST. LOUIS AREA AIPORTS DURING THE LATE EVENING AND EARLY
OVERNIGHT HOURS. THESE SHOWERS WILL ALSO BRING VISIBILITY
RESTRICTIONS AND CEILINGS BELOW 2000 FEET AGL. WINDS DURING THE
PERIOD ARE EXPECTED TO STAY BELOW 10 KNOTS, BUT A COLD FRONT WILL
MOVE THROUGH THE AREA CAUSING WINDS TO SHIFT OUT OF THE NORTH
AFTHER 06Z TONIGHT.
BRITT
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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