398
FXUS63 KLSX 221955
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
155 PM CST SUN DEC 22 2024
KEY MESSAGES
- SEVERAL ROUNDS OF RAIN ARE EXPECTED DURING THE HOLIDAY WEEK,
WITH THE BEST CHANCES (50-80%) CENTERED ON TUESDAY AFTERNOON -
CHRISTMAS MORNING IN PARTS OF EAST CENTRAL AND SOUTHEAST
MISSOURI AS WELL AS SOUTHWEST ILLINOIS.
- ABOVE NORMAL TEMPERATURES ARE FORECAST FOR THE ENTIRETY OF THE
HOLIDAY WEEK, WITH THE WARMEST TEMPERATURES FORECAST ON FRIDAY
AND SATURDAY WITH HIGHS WELL INTO THE 50S EACH AFTERNOON.
SHORT TERM
(THROUGH LATE MONDAY)
ISSUED AT 144 PM CST SUN DEC 22 2024
MILDER CONDITIONS ARE FORECAST TONIGHT AS MID/HIGH LEVEL CLOUDS
INCREASE AHEAD OF A MIDLEVEL SHORTWAVE TROUGH OVER THE UPPER
MIDWEST. AT THE SURFACE, THE PRESSURE GRADIENT TIGHTENS ACROSS THE
MID-MISSISSIPPI VALLEY AHEAD OF AN APPROACHING COLD FRONT. THIS WILL
YIELD STRONGER SOUTH/SOUTHWEST WINDS AT THE SURFACE. THESE WINDS
WILL HELP KEEP THE LOWER TROPOSPHERE WELL MIXED, AND COMBINED WITH
THE AFOREMENTIONED INCREASE IN CLOUD COVER, WILL HELP LIMIT THE
TEMPERATURE DROP TONIGHT. IN FACT, TEMPERATURES ARE LIKELY TO STEADY
OUT AND RISE AFTER MIDNIGHT IN MANY AREAS, WITH LOWS IN THE 30S
COMING GENERALLY BEFORE 2-3 AM.
THE COLD FRONT MAKES IT INTO PARTS OF NORTHEAST MISSOURI AND WEST-
CENTRAL ILLINOIS BY LATE MONDAY AFTERNOON, BUT LARGELY WASHES OUT
WITH VERY LITTLE/NO SURFACE CONVERGENCE ALONG/NEAR THE REMNANT
BOUNDARY. AHEAD OF THE FRONT, THERE IS WEAK LOW-LEVEL (~850 HPA)
MOISTURE CONVERGENCE AND SLIGHT COOLING ALOFT ASSOCIATED WITH SUBTLE
MIDLEVEL HEIGHT FALLS. CAMS SHOW SOME WEAK ECHOES ACROSS PARTS OF
THE AREA BENEATH THIS SUBTLE, WEAK FORCING. SOUNDINGS SHOW DRY AIR
BELOW THE CLOUD BASE (~5-8 KFT AGL), SUGGESTING LITTLE IF NOTHING
WILL REACH THE SURFACE. HAVE THEREFORE KEPT THE FORECAST DRY THROUGH
THE DAY ON MONDAY, THOUGH CANNOT RULE OUT A FEW STRAY SPRINKLES.
HIGHS MONDAY AFTERNOON ARE FORECAST TO BE ABOUT 5 DEGREES WARMER
THAN THIS AFTERNOON, MAINLY DUE TO THE WARMER START TO THE DAY.
THICK CLOUD COVER WITH LOWERING CEILINGS DURING THE DAY SHOULD
PREVENT TOO MUCH IN THE WAY OF SOLAR INSOLATION, LIMITING THE
WARMUP. HIGHS ARE EXPECTED TO RANGE FROM THE MID TO UPPER 40S, WITH
SOME SPOTS TOPPING OUT AROUND THE 50 DEGREE MARK IN PARTS OF CENTRAL
AND EAST-CENTRAL MISSOURI.
GOSSELIN
LONG TERM
(MONDAY NIGHT THROUGH NEXT SUNDAY)
ISSUED AT 144 PM CST SUN DEC 22 2024
(MONDAY NIGHT - CHRISTMAS DAY)
CHANCES OF LIGHT RAIN INCREASE MONDAY NIGHT, MAINLY AFTER MIDNIGHT
AS A MIDLEVEL SHORTWAVE TROUGH APPROACHES FROM THE SOUTH-CENTRAL
PLAINS. LIFT IS EXPECTED TO INCREASE DOWNSTREAM OF THIS FEATURE, AND
COMBINED WITH INCREASING LOW-LEVEL CONVERGENCE IN THE VICINITY OF A
STATIONARY FRONT, SHOULD PRODUCE WIDESPREAD LIGHT RAIN. THERE IS
SOME UNCERTAINTY HOWEVER WITH RESPECT TO THE LOCATION OF THIS LIGHT
RAIN, WITH THE GFS/GEFS FURTHER NORTHWEST THAN THE NAM/ECMWF/EPS.
LEANED TOWARD THE OVERALL BROAD CONSENSUS, FAVORING PORTIONS OF
SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS WITH THE HIGHEST POPS (40-
60%) AFTER MIDNIGHT. A FURTHER SOUTHEAST AXIS OF LIGHT RAINFALL IS
ALSO SUPPORTED BY 12Z CAMS. IN ADDITION, THE SURFACE FRONT SHOULD BE
ABLE TO SAG INTO SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS WITH WEAK
SOUTHEAST MID/UPPER LEVEL RIDGING AND FALLING MID/UPPER LEVEL
HEIGHTS ACROSS THE UPPER OHIO VALLEY/MID ATLANTIC.
LIGHT RAIN SHOULD BE VERY PERSISTENT ON TUESDAY, WITH THE MIDLEVEL
SHORTWAVE VERY SLOWLY MOVING EASTWARD OUT OF THE SOUTH-CENTRAL
PLAINS. THE STRONGEST MID/UPPER LEVEL FORCING ACROSS OUR AREA
ACTUALLY LOOKS TO BE TUESDAY NIGHT AS THE SHORTWAVE MOVES INTO
NORTHWEST ARKANSAS AND DIVERGENCE INCREASES ALOFT BENEATH THE RIGHT-
ENTRANCE REGION OF AN UPPER-LEVEL JET STREAK. THIS WILL HELP SPREAD
THE LIGHT RAIN FURTHER TO THE NORTH IN TIME.
MODEL GUIDANCE IS IN PRETTY GOOD AGREEMENT WITH THE TRACK AND TIMING
OF THIS SHORTWAVE AND ASSOCIATED IMPACTS. THERE ARE HOWEVER STILL
SOME SUBTLE DIFFERENCES, INCLUDING HOW FAR NORTHWEST THE RAIN SHIELD
GETS AND THE END TIMING OF RAIN LATE TUESDAY NIGHT INTO CHRISTMAS
DAY. AS DISCUSSED A BIT IN THE MONDAY NIGHT TIME PERIOD, THE
GFS/GEFS IS FARTHER NORTHWEST THAN THE ECMWF/EPS WITH THE RAIN LATE
MONDAY NIGHT AND THIS CONTINUES THROUGH MUCH OF THE DAYLIGHT HOURS
ON TUESDAY. THE GFS APPEARS TO BE TOO FAR NORTHWEST WITH THE
STATIONARY FRONT, SO LEANED CLOSER TO THE ECMWF/EPS SOLUTION WHICH
SHOWS THE NORTHWESTERN EDGE OF THE STEADIER LIGHT RAIN MOVING INTO
EAST-CENTRAL MISSOURI AND SOUTH-CENTRAL ILLINOIS BY TUESDAY
AFTERNOON.
THE TIMING OF THE WAVE APPROACHING THE MISSISSIPPI RIVER HAS ALSO
VARIED BY ABOUT 6 HOURS IN MODEL GUIDANCE, BUT A GENERAL CONSENSUS
IS FOR IT TO REACH THE RIVER AROUND MIDDAY. WITH CONTINUING LOW-
LEVEL MOISTURE CONVERGENCE NEAR THE STATIONARY FRONT ACROSS
SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS, WOULD EXPECT LIGHT RAIN
TO CONTINUE INTO THE MORNING HOURS IN THESE LOCATIONS. THE CHANCE OF
RAIN SHOULD SHUT DOWN BY OR JUST AFTER MIDDAY HOWEVER, AS MID/UPPER
LEVEL SUBSIDENCE SETS IN BEHIND THE DEPARTING SHORTWAVE AND THE
SURFACE FRONTAL BOUNDARY LOSES ITS DEFINITION.
WHILE RAIN LOOKS PERSISTENT ACROSS EAST CENTRAL AND SOUTHEAST
MISSOURI AS WELL AS SOUTHWEST ILLINOIS, IT DOES LOOK LIGHT.
PROBABILITIES FOR A HALF OF AN INCH THROUGH CHRISTMAS DAY ARE 30-70%
ACROSS SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS, BUT DROP TO 10-20%
FOR AN INCH OR MORE OF RAINFALL.
THE OTHER STORY IN/AROUND THE CHRISTMAS HOLIDAY WILL BE THE MILD
TEMPERATURES. HOWEVER, PLENTY OF LOW CLOUD COVER AND PERSISTENT RAIN
WILL REALLY HAMPER THE TEMPERATURE RISE DURING THE DAY. HIGHS ARE
FORECAST TO BE MAINLY IN THE 40S, THOUGH SOME SPOTS ESPECIALLY
CHRISTMAS DAY VERY WELL MAY APPROACH OR JUST TOP 50 DEGREES. THESE
READINGS WOULD BE ABOUT 5-10 DEGREES ABOVE NORMAL FOR LATE DECEMBER.
NIGHTTIME LOWS CHRISTMAS EVE NIGHT HOWEVER ARE ONLY EXPECTED TO DROP
BACK INTO THE MID 30S TO LOW 40S, OR CLOSER TO 10-15 DEGREES ABOVE
NORMAL FOR THE DATE.
(CHRISTMAS NIGHT - THURSDAY)
A RELATIVELY SHORT PERIOD OF QUIET, MILD, AND DRY WEATHER LOOKS IN
STORE FOR CHRISTMAS NIGHT THROUGH THURSDAY AS A MID/UPPER LEVEL
RIDGE MOVES ACROSS THE MISSISSIPPI VALLEY. TEMPERATURES ARE EXPECTED
TO CONTINUE TO GRADUALLY MODERATE, WITH HIGHS REACHING INTO THE 50S
ON THURSDAY.
(THURSDAY NIGHT - NEXT SUNDAY)
THE ACTIVE PATTERN CONTINUES HOWEVER WITH ANOTHER MIDLEVEL SHORTWAVE
TROUGH MOVING NORTHEAST OUT OF THE PLAINS THURSDAY NIGHT. MODEL
GUIDANCE HAS MORE SPREAD WITH THIS FEATURE, BOTH IN TERMS OF TRACK
AND TIMING. THE GFS IS ABOUT 6 HOURS FASTER AND 250 MILES FURTHER
NORTH COMPARED TO THE ECMWF FOR REFERENCE. GIVEN FAST FLOW ACROSS
THE CONUS AND SHORT WAVELENGTHS BETWEEN SUCCESSIVE SHORTWAVES, THIS
TYPE OF SPREAD IS NOT SURPRISING. CLUSTERS OF THE 500-HPA HEIGHT
PATTERN SEEM TO FAVOR THE SLOWER SOLUTION MORE, WITH ABOUT 70% OF
MEMBERS FROM THE LREF HAVING TIMING MORE SIMILAR TO THE ECMWF.
HOWEVER, THERE IS STILL A FAIR ABOUT OF TRACK DISAGREEMENT AMONGST
THESE 3 CLUSTERS.
THE GOOD NEWS FOR OUR AREA IS BOTH OF THESE SCENARIOS SHOULD PRODUCE
WIDESPREAD RAINFALL, THOUGH THE FURTHER NORTHWEST SOLUTION SIMILAR
TO THE OPERATIONAL GFS MAY ALSO BE ACCOMPANIED BY A LOW CHANCE OF
THUNDER. PROBABILITIES FOR MEASURABLE RAIN THURSDAY NIGHT INTO
FRIDAY MORNING ARE 90-100% ACROSS THE ENTIRE AREA ON THE LREF. THE
LATEST NBM POPS HAVE COME UP A BIT (40-60%), AND THESE POPS LIKELY
WILL NEED TO BE BOOSTED AS WE GET CLOSER IN TIME AS TIMING
DIFFERENCES DECREASE WITHIN MODEL GUIDANCE. THIS ROUND OF RAIN ALSO
LOOKS TO BE ON THE LIGHTER SIDE, MAINLY DUE TO A SHORTER DURATION OF
RAINFALL. CHANCES FOR A HALF INCH OF RAIN OR MORE RANGE FROM 20%
(NORTHEAST MISSOURI/WEST CENTRAL ILLINOIS) TO 40% (SOUTHEAST
MISSOURI/SOUTHWEST ILLINOIS).
THERE IS A THIRD IN THE SERIES OF MIDLEVEL SHORTWAVE TROUGHS WHICH
WILL IMPACT THE REGION SOMETIME BETWEEN FRIDAY NIGHT AND SATURDAY
NIGHT. NOT SURPRISINGLY, ENSEMBLE SPREAD WITH THE
TIMING/TRACK/STRENGTH OF THIS FEATURE IS EVEN HIGHER GIVEN THAT IT
IS FURTHER OUT IN TIME. WHILE THE SPECIFICS WILL NEED TO BE IRONED
OUT IN THE DAYS AHEAD, IT APPEARS LIKE THERE WILL BE ANOTHER ROUND
OF WIDESPREAD RAINFALL IN THIS TIME PERIOD ACROSS MUCH, IF NOT ALL,
OF THE REGION. THERE MAY ALSO BE A LOW THREAT FOR THUNDER WITH THIS
ROUND, THOUGH LEFT OUT OF THE FORECAST FOR NOW GIVEN THE HIGH
DEGREE OF MODEL SPREAD.
DRY WEATHER ALONG WITH SLIGHTLY COOLER (THOUGH STILL WELL-ABOVE
NORMAL) TEMPERATURES ARE FAVORED FOR NEXT SUNDAY.
GOSSELIN
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1101 AM CST SUN DEC 22 2024
BRISK SOUTHERLY WINDS WITH SOME GUSTS AROUND 20 KNOTS ARE FORECAST
THROUGH MUCH OF THE PERIOD. THESE STRONGER WINDS/GUSTS SHOULD
PRECLUDE ANY LOW-LEVEL WIND SHEAR OVERNIGHT TONIGHT.
OTHERWISE, DRY WEATHER WILL CONTINUE THROUGH MONDAY MORNING.
MID/HIGH LEVEL CLOUDS WILL INCREASE TONIGHT, WITH CEILING
GRADUALLY LOWERING THROUGH THE PERIOD. MOST GUIDANCE SUGGESTS SOME
MVFR CEILINGS ALONG A WASHED-OUT FRONTAL BOUNDARY ON MONDAY, BUT
WAS NOT CONFIDENT ENOUGH TO ADD TO ANY OF THE TERMINALS AT THIS
TIME. FOR NOW, HAVE A SCT025 GROUP IN THERE STARTING MID MORNING
AT KCOU/KJEF/KUIN. FOR THE METRO TERMINALS, BEST CHANCES OF ANY
MVFR CEILINGS LOOKS TO BE CLOSER TO OR JUST AFTER MIDDAY MONDAY.
GOSSELIN
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page