914
FXUS63 KLSX 172331
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
531 PM CST TUE DEC 17 2024
KEY MESSAGES
- LIGHT RAINFALL IS EXPECTED ACROSS MUCH OF THE AREA TONIGHT, ENDING
BY SUNRISE WEDNESDAY MORNING.
- TEMPERATURES WILL TREND COLDER THROUGH SATURDAY BEFORE WARMING
GRADUALLY NEXT WEEK.
SHORT TERM
(THROUGH LATE WEDNESDAY NIGHT)
ISSUED AT 230 PM CST TUE DEC 17 2024
AFTERNOON WATER VAPOR IMAGERY SHOWS A TROUGH DIGGING EQUATORWARD
OVER THE HIGH PLAINS. AHEAD OF THIS TROUGH MOVING EASTWARD THIS
EVENING AND TONIGHT, SURFACE HIGH PRESSURE HAS SHIFTED EASTWARD OUT
OF THE AREA DEEPER INTO THE OHIO VALLEY. BETWEEN THAT AND A
DEEPENING SURFACE LOW OVER THE CENTRAL PLAINS, LOW-LEVEL FLOW HAS
BECOME SOUTHERLY, ADVECTING WARM, MOIST AIR INTO THE MIDDLE
MISSISSIPPI VALLEY. THIS HAS RESULTED IN TEMPERATURES WARMING INTO
THE MID-50S FOR MOST LOCATIONS AND THE INCREASING CLOUD COVER FROM
SOUTHWEST TO NORTHEAST THIS AFTERNOON PER VISIBLE SATELLITE.
AS THE LOW DEEPENS FURTHER AND MOVES TOWARD THE MIDDLE MISSISSIPPI
VALLEY, WARM AIR ADVECTION WILL ONLY INCREASE ACROSS THE REGION
AMONG WEAK FORCING, CAUSING WIDELY SCATTERED LIGHT RAIN TO DEVELOP
THIS EVENING, WITH THE FIRST HINTS OF THIS ACTIVITY SHOWING UP ON
RADAR ACROSS SOUTHWESTERN MISSOURI. THE CENTER OF THE LOW WILL SLIP
THROUGH SOUTHERN PORTIONS OF THE CWA TONIGHT, DRAGGING A COLD FRONT
WITH IT. AS BOTH THE LOW AND FRONT ENTER THE OHIO VALLEY, FORCING
ALOFT VIA THE TROUGH AND A JET STREAK WILL AMPLIFY LIFT AND PRODUCE
MORE WIDESPREAD RAINFALL ACROSS FAR SOUTHEASTERN MISSOURI AND
SOUTHWESTERN ILLINOIS JUST SOUTHEAST OF THE CWA. RAINFALL IS
EXPECTED TO END ACROSS THE CWA BY AROUND DAYBREAK WEDNESDAY, WITH
THE 12Z HREF PROBABILITY OF 0.01" OF ACCUMULATION TOPPING OUT AT 90%
BUT FALLING OF QUICKLY WITH INCREASING ACCUMULATION THRESHOLDS. SO
WHILE CONFIDENCE IS HIGH THAT MOST LOCATIONS WILL SEE RAIN, A
SOAKING RAIN IS NOT EXPECTED.
IN THE WAKE OF TONIGHT'S SYSTEM, DEEP NORTHWESTERLY FLOW WILL SETTLE
INTO THE REGION, PUSHING TEMPERATURES DOWN CLOSER TO CLIMATOLOGICAL
NORMALS. THIS NORTHWESTERLY FLOW WILL ALSO USHER IN DRIER AIR, WITH
CLOUDS GRADUALLY CLEARING FROM NORTH TO SOUTH THROUGH THE DAY.
ELMORE
LONG TERM
(THURSDAY THROUGH NEXT TUESDAY)
ISSUED AT 230 PM CST TUE DEC 17 2024
AN AMPLIFYING SHORTWAVE WILL BE DIVING SOUTHEASTWARD THROUGH THE
MIDWEST ON THURSDAY PER GUIDANCE CONSENSUS. A MAJORITY OF ENSEMBLE
MEMBERS FAVOR ITS ASSOCIATED SURFACE LOW AND PRECIPITATION SHIELD
PASSING JUST NORTH OF THE CWA, WITH ENSEMBLE-BASED PROBABILITIES OF
0.01" OF QPF TOPPING OUT AT 25% ACROSS FAR NORTHEASTERN PORTIONS OF
THE CWA THURSDAY EVENING. GIVEN THE EXPECTED TRAJECTORY OF THE
SURFACE LOW, THE CWA WILL BE WITHIN THE WARM SECTOR FOR MUCH OF THE
DAY, WITH SOUTHERLY FLOW HELPING BOOST TEMPERATURES ABOVE WHAT IS
FORECAST FOR WEDNESDAY. WHILE THERE IS STILL ABOUT 5-7 DEGREES
BETWEEN THE 25TH AND 75TH PERCENTILE AMONG ENSEMBLE GUIDANCE,
MEMBERSHIP IS CLUSTERED AROUND HIGHS IN THE MID 40S FOR MUCH OF THE
CWA.
A COLD FRONT WILL ACCOMPANY THE AFOREMENTIONED SURFACE LOW, PUSHING
TEMPERATURES DOWN TO AT OR JUST BELOW CLIMATOLOGICAL NORMALS FOR
FRIDAY, WHICH IS SET TO BE THE COLDEST DAY OF THE FORECAST PERIOD.
DEEP NORTHWESTERLY FLOW WILL PERSIST OVER THE REGION THROUGH
SATURDAY, KEEPING TEMPERATURES AT OR BELOW SEASONAL NORMALS.
ENSEMBLE CLUSTERS AND DETERMINISTIC GUIDANCE CONTINUE TO SUPPORT
UPPER-LEVEL RIDGING BUILDING INTO THE REGION STARTING SUNDAY INTO
EARLY NEXT WEEK, CAUSING TEMPERATURES TO GRADUALLY REBOUND.
ELMORE
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 506 PM CST TUE DEC 17 2024
CIGS ARE GRADUALLY LOWERING FROM SOUTH TO NORTH AS WEAK SOUTHERLY
LOW-LEVEL WINDS ADVECT MOISTURE INTO THE REGION. A FEW LIGHT
SHOWERS ARE CURRENTLY EVIDENT ON RADAR EMBEDDED IN THE STRATUS,
AND THEIR COVERAGE IS EXPECTED TO BROADEN WITH TIME THIS EVENING
IMPACTING THE ST. LOUIS TERMINALS AND KUIN THROUGH THE NIGHT. IT
WILL NOT BE RAINING CONSTANTLY, AND VISIBILITIES SHOULD NOT
DEGRADE TOO MUCH. HOWEVER, CIGS WILL LOWER TO MVFR CATEGORIES
(PERHAPS FUEL-ALTERNATE LEVELS INTERMITTENTLY) AT ALL TERMINALS
EXCEPT FOR KUIN. AN ISOLATED THUNDERSTORM OR TWO ARE POSSIBLE, BUT
WILL STAY FAR SOUTH OF THE TAF SITES.
AS THE SURFACE LOW THAT IS THE CAUSE OF OUR SENSIBLE WEATHER
TRACKS EAST WEDNESDAY MORNING, WINDS WILL SHIFT OUT OF THE NORTH
AND CIGS WILL GRADUALLY IMPROVE TO VFR CONDITIONS BY THE EARLY
AFTERNOON. THERE REMAINS A LOW THREAT FOR BRIEF MVFR CONDITIONS
IN THE EARLY AFTERNOON AS A WEAK COLD FRONT POOLS SOME LOW-LEVEL
MOISTURE ACROSS CENTRAL AND EASTERN MISSOURI, BUT CONFIDENCE IN
THIS CAUSING IMPACTFUL CIGS IS STILL VERY LOW AND WAS KEPT OUT OF
THE TAFS.
MRB
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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