820
FXUS63 KLSX 180422
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
1022 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 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1014 PM CST TUE DEC 17 2024
SHOWERS HAVE BLOSSOMED ALONG A WARM FRONT DRAPED JUST SOUTH OF THE
ST. LOUIS AND CENTRAL MISSOURI TERMINALS. RIGHT ON THE NOSE OF A
LOW-LEVEL JET, TAPPING INTO VERY WEAK INSTABILITY, A THUNDERSTORM
DID INDEED DEVELOP AND IMPACT KCPS. OTHERWISE, PRECIPITATION IS
DEVELOPING AS EXPECTED. CIGS, HOWEVER, ARE TAKING LONGER TO DROP
THAN FORECAST. WHILE MVFR CONDITIONS EXIST JUST SOUTH OF THE WARM
FRONT, LOW-END VFR CONDITIONS REMAIN IN PLACE AT THE TAF SITES.
CONDITIONS ARE STILL FORECAST TO DEGRADE, THOUGH THE MVFR ONSET
WAS PUSHED BACK A FEW HOURS INTO THE EARLY MORNING. KUIN WILL
REMAIN VFR AND LARGELY DRY TONIGHT, HOWEVER A MID-LEVEL WAVE
ACROSS IOWA IS LOOKING INCREASINGLY LIKELY TO DRAW MVFR CONDITIONS
INTO EASTERN MISSOURI AND WESTERN ILLINOIS DURING THE EARLY
AFTERNOON ON WEDNESDAY. AS SUCH, A WINDOW OF MVFR WAS ADDED AFTER
A BRIEF IMPROVEMENT IN THE LATE MORNING. WITH HIGH PRESSURE
SLOWLY MOVING IN AFTER THIS, VFR CONDITIONS SHOULD RETURN BY THE
END OF THE FORECAST PERIOD.
MRB
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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