853
FXUS63 KLSX 202017
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
217 PM CST FRI DEC 20 2024
KEY MESSAGES
- SEASONABLY COLD WEATHER WILL CONTINUE THROUGH EARLY SUNDAY, WITH
A WARM-UP TO ABOVE NORMAL TEMPERATURES COMMENCING ON SUNDAY AND
PERSISTING THROUGH MUCH OF NEXT WEEK.
- AN ACTIVE WEATHER PATTERN WILL RESULT IN MULTIPLE RAIN CHANCES
THROUGHOUT NEXT WEEK INCLUDING CHRISTMAS EVE AND CHRISTMAS
MORNING.
SHORT TERM
(THROUGH LATE SATURDAY NIGHT)
ISSUED AT 202 PM CST FRI DEC 20 2024
A RELATIVELY AMPLIFIED FLOW REGIME WILL CONTINUE OVER MUCH OF THE
CONUS THROUGH SATURDAY WITH A SLOWLY PROGRESSIVE LONGWAVE TROF
CENTERED THROUGH THE EASTERN U.S.. AS THIS TROF NUDGES EASTWARD
TONIGHT, A SHORT-WAVE WILL DIVE SOUTHEASTWARD FROM THE NORTHERN
ROCKIES AND TRAVERSE THE MIDDLE MISSISSIPPI VALLEY EARLY ON
SATURDAY MORNING. OTHER THAN WEAK LARGE SCALE FORCING, THERE IS A
LACK OF COHERENT FRONTOGENETICAL FORCING AND AMPLE MOISTURE WHICH
MIGHT REFLECT A LIGHT SNOW THREAT. STRATUS WILL CLEAR NON
UNIFORMLY TONIGHT WITH THE CLEARING LARGELY INITIATING TO THE E/NE
AND CLEARING WESTWARD, AND CLOUDS REMAINING OVER THE WESTERN CWA
INTO THE EARLY SATURDAY MORNING. THE AFOREMENTIONED WEAK MID-LEVEL
FORCING AND MID-LEVEL MOISTURE MOVING ATOP RESIDUAL LOWER STRATUS
POISED IN THE WESTERN CWA COULD EEK OUT A FEW FLURRIES IN THIS
AREA. OTHERWISE ATTENDANT WITH PROGRESSION OF THE UPPER TROF, A
LARGE SURFACE HIGH WILL SETTLE INTO THE MISSISSIPPI VALLEY TONIGHT
AND DOMINATE THE REGION ON SATURDAY. TEMPERATURES ON SATURDAY
WON'T BE AS COLD AS TODAY OWING TO A LACK OF CLOUDS/MORE SUN AND
NEUTRAL TEMPERATURE ADVECTION. THE AFOREMENTIONED SURFACE HIGH
WILL SLOWLY RETREAT EASTWARD ON SATURDAY NIGHT WITH THE ONSET OF
WEAK WAA ALOFT AND SURFACE WINDS VEERING TO SOUTHEASTERLY.
GLASS
LONG TERM
(SUNDAY THROUGH NEXT FRIDAY)
ISSUED AT 202 PM CST FRI DEC 20 2024
THE PATTERN ACROSS THE CONUS BECOMES EVEN MORE PROGRESSIVE
HEADING THROUGH SUNDAY-SUNDAY NIGHT WITH MID-UPPER LEVEL HEIGHT
RISES AND A RETURN TO MORE OF A ZONAL COMPONENT. THIS WILL ALLOW A
MORE PROMINENT LOW-LEVEL WAA REGIME TO ENSUE ON SUNDAY, HOWEVER
SOUTHEASTERLY SURFACE WINDS AND SHALLOW MIXING (AOB 2KFT) WILL
LIMIT WHAT OTHERWISE MIGHT BE A MORE SUBSTANTIAL WARM-UP GIVEN THE
SOUTHWEST FLOW ABOVE THE BOUNDARY LAYER. TEMPERATURES WILL BE
WARMER WITH HIGHS REBOUNDING INTO THE 40S, NEAR TO 5+ DEGREES
ABOVE NORMAL.
MONDAY THROUGH NEXT WEEK WILL BE AN ACTIVE PERIOD FEATURING MULTIPLE
RAIN CHANCES. THE INITIAL THREAT OF RAIN WILL EVOLVE ON MONDAY
AFTERNOON AND ESPECIALLY MONDAY NIGHT AND OCCUR IN THE WAKE OF A
SHORTWAVE TROF PASSAGE TO OUR NORTH AND AHEAD OF THE ASSOCIATED
ADVANCING COLD FRONT. THE PRIMARY REGION IS ACROSS THE SOUTHERN HALF
OF THE CWA, ESPECIALLY SE MO AND SRN IL, LARGELY DUE TO LOW-LEVEL
WAA AND LOW-LEVEL MOISTURE CONVERGENCE AND TRANSPORT.
DETAILS IN SPECIFICS DIMINISH TUESDAY THROUGH FRIDAY IN THIS ACTIVE
REGIME WITH A SERIES OF UPPER LOWS/TROFS TRAVERSING THE LOW/MID
MISSISSIPPI VALLEY REGION, THE FIRST CENTERED AROUND
WEDNESDAY/CHRISTMAS DAY AND ANOTHER LATE THURSDAY INTO FRIDAY. THE
ENSEMBLE CLUSTER ANALYSIS SHOWS QUITE A BIT OF VARIABILITY IN THE
TIMING AND LATITUDE OF THE TROF POSITIONS, WHICH IMPACT THE TIME
FRAME OF RAINFALL AS WELL AS THE NORTHERN EXTENT. THE LATEST
GUIDANCE AND LREF SUITE WHILE CONTINUING TO SHOW DIFFERENCES HAS
SUGGESTED A MORE NORTHERN TRACK ON THE EJECTING TROF ON CHRISTMAS
DAY AND SUGGESTS POTENTIALLY A LARGER ALL RAIN FOOTPRINT. BOTH THE 6
HOUR AND 24 HOUR EXCEEDANCE PROBABILITIES FROM THE 100-MEMBER LREF
ARE SHOWING GREATER PROBABILITIES OF MEASURABLE RAINFALL (50-90+
PERCENT), ESPECIALLY 06-18Z WEDNESDAY. THE LATE WEEK SYSTEM DISPLAYS
THE SAME UNCERTAINTIES IN TROF POSTION/TIMING WITH EXCEEDANCE
PROBABILITIES FROM THE LREF SHOWING 60-70% OF THE MEMBERSHIP
PRODUCING MEASURABLE RAINFALL.
TEMPERATURES THROUGHOUT NEXT WEEK LOOK MILD BY LATE DECEMBER
STANDARDS. THE ENTIRE INTERQUARTILE RANGE (IQR) OF NBM MAX TEMP
GUIDANCE IS ABOVE NORMAL WED-FRI WITH HIGHS IN THE UPPER 40S TO
50S.
GLASS
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1125 AM CST FRI DEC 20 2024
STRATUS RESULTING IN MVFR CIGS/FLIGHT CONDITIONS DOMINATED THE
AREA LATE THIS MORNING AND WAS IMPACTING ALL OF THE TERMINALS.
THERE WILL BE SOME CLEARING DURING THIS PERIOD HOWEVER IT WILL NOT
BE UNIFORM. CLEARING AT KUIN AND THE ST. LOUIS METRO TERMINALS
IS EXPECTED AROUND 06Z AND WILL OCCUR FROM THE EAST/NORTHEAST.
UNTIL THEN MVFR CIGS WILL PREVAIL. KCOU AND KJEF ARE CURRENTLY
NEAR THE WESTERN EDGE OF THE CLOUD COVER AND PRESENT INDICATIONS
ARE IT WILL ERODE EARLY THIS AFTERNOON AND THESE SITES WILL THEN
BE VFR UNTIL LATE EVENING WHEN THE MVFR STRATUS RETURNS FROM THE
EAST. KCOU/KJEF SHOULD THEN CLEAR ON SATURDAY MORNING.
GUSTY NORTHWEST WINDS SHOULD DIMINISH LATE AFTERNOON-EARLY THIS
EVENING BECOMING LIGHT AND VARIABLE LATER TONIGHT.
GLASS
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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