147
FXUS63 KARX 242340
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
540 PM CST TUE DEC 24 2024
KEY MESSAGES
- CLOUDY CONDITIONS CONTINUE INTO THE WEEKEND WITH HIGH
TEMPERATURES RISING INTO THE 40S, NEARING 50F SOUTH OF I-90 BY
SATURDAY. LOW TEMPERATURES RISE ABOVE FREEZING BY THURSDAY
NIGHT, REMAINING ABOVE FREEZING INTO NEXT WEEK.
- A PERIOD OF FREEZING DRIZZLE IS POSSIBLE (0-20%) WEDNESDAY
AFTERNOON INTO THE OVERNIGHT HOURS, LARGELY DEPENDENT ON
TEMPERATURE.
- PRECIPITATION CHANCES (50-80%) RETURN THURSDAY INTO FRIDAY
WITH RAIN BEING THE EXPECTED PRECIPITATION TYPE. ADDITIONAL
CHANCES FOR PRECIPITATION CONTINUE INTO NEXT WEEK.
DISCUSSION
ISSUED AT 210 PM CST TUE DEC 24 2024
CLOUDY CONDITIONS AND WARMING TEMPERATURES
AMPLE LOW LEVEL MOISTURE IS DEPICTED IN NEARLY EVERY MODEL
SOLUTION IN THE SURFACE TO ~3KFT LAYER THROUGH THE REST OF THE
WEEK. THIS SUGGESTS THE LOW STRATUS OF TODAY WILL STICK AROUND
AS WE HEAD INTO THE WEEKEND. THE BIGGEST DISCREPANCY IN CLOUD
AMOUNTS REMAINS BETWEEN THE 24.06Z GEFS AND 24.06Z EPS FOR
WEDNESDAY IN THE WHICH SOME GEFS MEMBERS SUGGEST THE POTENTIAL
FOR CLEAR SKIES TODAY INTO WEDNESDAY WHILE OTHERS INDICATE
OVERCAST SKIES. THE EPS MEMBERS ARE IN MUCH BETTER AGREEMENT,
WITH EVERY MEMBER INDICATING 100% SKY COVER THROUGHOUT THE WEEK.
THE GEFS MEMBERS JOIN IN ON THIS SOLUTION BY LATE WEDNESDAY.
SOME MEMBERS OF BOTH ENSEMBLES BEGIN TO INDICATE SOME CLEARING
ON SUNDAY.
WINDS TURN SOUTHEASTERLY TO SOUTHERLY ON THE BACKSIDE OF
DEPARTING HIGH PRESSURE AND UPPER RIDGING TONIGHT AND WILL
BEGIN TO ADVECT WARM AIR INTO THE REGION TONIGHT AND WEDNESDAY.
HIGH TEMPERATURES BEGIN TO CLIMB ABOVE FREEZING AND INTO THE 40S
TOWARDS THE END OF THE WEEK IN RESPONSE, WITH AREAS SOUTH OF
I-90 POSSIBLY REACHING 50F BY SATURDAY AS THE NBM SUGGESTS A
40-80% PROBABILITY OF EXCEEDING 45F. ENSEMBLE GUIDANCE IS IN
GOOD AGREEMENT REGARDING TEMPERATURES OVER THE NEXT SEVERAL
DAYS, WITH ONLY A 2-5 DEGREE SPREAD IN THE 25TH-75TH PERCENTILES
IN THE NBM AND GEFS/EPS. THINKING THAT WE MAY TREND TOWARDS THE
75TH PERCENTILE FOR TEMPERATURES OVER THE NEXT FEW DAYS THOUGH
GIVEN THE EXPECTED CLOUDY SKIES AND PERSISTENT SOUTHERLY WINDS.
FREEZING DRIZZLE POTENTIAL
THE THREAT OF FREEZING DRIZZLE REMAINS FOR THE AFTERNOON AND
OVERNIGHT HOURS OF CHRISTMAS DAY. AS PREVIOUSLY MENTIONED,
MODEL SOUNDINGS DEPICT A WELL SATURATED SURFACE TO ~3KFT LAYER.
THE RAP INDICATES A REGION OF ISENTROPIC ASCENT WITHIN THIS
SATURATED LAYER ON THE 280K THETA SURFACE, MOVING NORTHWARD WITH
TIME WHICH MAY PROVIDE ENOUGH LIFT FOR PRECIPITATION TO FALL.
THE 24.12Z HREF JOINT PROBABILITIES OF TEMPERATURES < 32F AND
MEASURABLE PRECIPITATION RANGE FROM 0-20%, SO THIS IS NOT A HIGH
CONFIDENCE SCENARIO. WHETHER ANY PRECIPITATION IS FREEZING OR
NOT WILL BE LARGELY DEPENDENT ON HOW WARM THE LOW LEVELS GET
WEDNESDAY AFTERNOON AND HOW WARM THEY REMAIN INTO THURSDAY
MORNING.
PRECIPITATION CHANCES THURSDAY AND FRIDAY AND AGAIN NEXT WEEK
A 500HPA TROUGH CURRENTLY OFF THE WEST COAST OF THE UNITED STATES AS
SEEN IN WATER VAPOR IMAGERY WILL MOVE EASTWARD INTO THE
INTERMOUNTAIN WEST AND EJECT INTO THE PLAINS ON THURSDAY BEFORE
PROPAGATING NORTHWARD THURSDAY NIGHT INTO FRIDAY. FORCING ASSOCIATED
WITH THIS TROUGH COMBINED WITH PWATS IN THE 99.5TH PERCENTILE FOR
THIS TIME OF YEAR BRINGS THE CHANCE FOR MEASURABLE PRECIPITATION TO
THE AREA (50-80%), WHICH IS EXPECTED TO BE ALL RAIN GIVEN THE
PREVIOUSLY MENTIONED WARM AIR ADVECTION AHEAD OF THIS FEATURE. THE
AXIS OF HIGHEST QPF IS CURRENTLY EXPECTED FROM NORTHEAST IOWA INTO
CENTRAL WISCONSIN WITH TOTAL MEAN AMOUNTS OF 0.25-0.3 INCHES WITHIN
THIS AXIS ALTHOUGH 0.2 INCHES IS POSSIBLE ELSEWHERE. NBM
PROBABILITIES SUGGEST A 40-50% CHANCE OF EXCEEDING 0.3 INCHES
WITHIN THIS AXIS OF HIGHER AMOUNTS AREAS AND A 20-30% CHANCE TO
EXCEED 0.5 INCHES. ADDITIONAL SHORTWAVES TRAVERSE THROUGH THE
MEAN FLOW OVER THE WEEKEND SUCH THAT PRECIPITATION CHANCES
CONTINUE THROUGHOUT THE WEEKEND AND MAY BUMP UP THE OVERALL
PRECIPITATION AMOUNTS THROUGH THE WEEKEND.
THE NEXT BEST CHANCES FOR PRECIPITATION RETURN EARLY NEXT WEEK AS
ANOTHER 500HPA TROUGH MOVES INTO THE REGION. THERE IS STILL QUITE A
BIT OF UNCERTAINTY SURROUNDING THIS NEXT SYSTEM AS DETERMINISTIC
GUIDANCE HAS VARIOUS SOLUTIONS REGARDING TIMING AND LOCATION. THE
WPC CLUSTER ANALYSIS IS STILL IN GOOD AGREEMENT REGARDING THIS
TROUGH/SYSTEM DEVELOPING, BUT THE UNCERTAINTY IN TRACK AND TIMING
LEADS TO MULTIPLE POSSIBILITIES FOR PRECIPITATION TYPE. THE
CURRENT TRACK SEEN IN THE NBM SUGGESTS A WINTRY MIX SCENARIO
ACROSS OUR AREA, BUT DETAILS REGARDING THIS POSSIBILITY WILL
CONTINUE TO BECOME CLEARER IN THE COMING DAYS.
AVIATION /00Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 533 PM CST TUE DEC 24 2024
SURFACE HIGH PRESSURE REMAINS OVER THE REGION WITH MVFR CEILINGS FOR
MUCH OF THE AREA, BUT ALSO SOME THINNING OR PATCHY BREAKS OVER PARTS
OF SOUTHWEST WISCONSIN. THE 24.12Z HREF HAS A SIGNAL FOR AREAS
OF FOG FROM THE MISSOURI RIVER VALLEY INTO NORTHWEST IA AND
WESTERN MN/NORTHERN WI. PATCHY 40-70% PROBABILITIES LOCALLY FOR
3SM OR LESS. LOW LEVEL MOISTURE REMAINS IN PLACE TONIGHT AND
WITH INCREASING LOW LEVEL MOISTURE TRANSPORT WEDNESDAY EVENING,
WHEN THE DEPTH OF THE MOISTURE INCREASES. MOST OF THE FORECAST
SOUNDINGS/HI-RES MODELS SHOW LOWERING OF CEILINGS FROM MVFR TO
IFR THIS EVENING OR OVERNIGHT. THE 900MB WINDS ARE SOMEWHAT
ELEVATED, BUT HAVE PATCHY FOG IN FOR NOW FOR PARTS OF SOUTHEAST
MN AND NORTHEAST IA AND NORTH OF I94. WINDS REMAIN LIGHT AND
VARIABLE OR LIGHT SOUTHEAST TONIGHT AND WEDNESDAY.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...FALKINHAM
AVIATION...ZAPOTOCNY
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