210
FXUS63 KARX 240446
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1046 PM CST MON DEC 23 2024
KEY MESSAGES
- LIGHT WINTRY MIX, LARGELY SNOW, EXITS EASTWARD THROUGH MID-
AFTERNOON. IMPACTS, WHILE LARGELY MINOR, WILL BE FOCUSED IN
WEST CENTRAL WI.
- FOG MAY OCCUR TONIGHT WITH VISIBILITIES POTENTIALLY (30%)
DROPPING BELOW 1 MILE.
- WARMER WEATHER FROM MID WEEK INTO THE COMING WEEKEND COULD
LEAD TO SOME DRIZZLE, FOG, AND RAIN, ESPECIALLY THE LATTER
HALF THE WEEK.
DISCUSSION
ISSUED AT 140 PM CST MON DEC 23 2024
THIS AFTERNOON AND TONIGHT - WINTRY MIX EXITS
COMPARED TO GUIDANCE YESTERDAY, BOTH ADDITIONAL MID-LEVEL DRY AIR
AND WARMER SURFACE TEMPERATURES BY ABOUT 1-3 DEGREES DELAYED ONSET
AND REDUCED COVERAGE/DURATION OF FREEZING DRIZZLE. THUS, WHILE A
MIXTURE OF EVERY PRECIP TYPE WAS REPORTED THIS MORNING, IMPACTS WERE
LIMITED.
OVER THE PAST COUPLE OF HOURS, AN AREA OF LIGHT SNOW HAS
DEVELOPED IN WEST CENTRAL WISCONSIN, INCLUDING LA CROSSE, BLACK
RIVER FALLS, CAMP DOUGLAS, NEW LISBON, AND AT TIMES SPARTA.
23.16Z RAP SOUNDINGS REFLECT THIS OUTCOME FAIRLY WELL WITH
SATURATION THROUGH THE ATMOSPHERE, INCLUDING TO THE DGZ, LIKELY
THE RESULT OF A COMBINATION OF FROZEN HYDROMETEORS FALLING INTO
THE MID-LEVEL DRY AIR INTRUSION AND COOLING ALOFT IN CLOSE
PROXIMITY TO THE APPROACHING UPPER WAVE. WITH MODEST 850MB
FRONTOGENESIS SEEN AROUND THE I-90/94 JUNCTION, SHOULD CONTINUE
TO SEE LIGHT TO OCCASIONALLY MODERATE SNOW OVER THE NEXT 2-3
HOURS WITHIN PORTIONS OF THE WINTER WEATHER ADVISORY AREA. THUS,
WHILE THE WINTER WEATHER ADVISORY WAS INITIALLY ISSUED
YESTERDAY FOR FREEZING DRIZZLE POTENTIAL, WILL KEEP IT GOING IN
DEFERENCE TO THE POTENTIAL FOR IMPACTS FROM LIGHT TO MODERATE
SNOW WITHIN THE SAME AREA.
TONIGHT, AS THE UPPER WAVE DEPARTS, LARGE SCALE DESCENT SHOULD OCCUR
WITH SURFACE HIGH PRESSURE AND CONCOMITANT LIGHT WINDS DEVELOPING.
GIVEN SNOW COVER ACROSS THE AREA AND ADDITIONAL SURFACE MOISTURE
FROM THIS MORNING, FOG AND/OR LOW STRATUS SHOULD DEVELOP. WHILE
MODELED MRI SUGGESTS STRATUS IS FAVORED, THE FRESH ADDITIONAL
MOISTURE FROM TODAY'S PRECIP DOES SUGGEST CAUTION IN RULING OUT FOG.
INDEED, 23.12Z HREF AND 23.09Z SREF BOTH SUGGEST AROUND A 30% CHANCE
FOR VISIBILITY BELOW 1 MILE. HAVE THEREFORE ELECTED TO KEEP PATCHY
FOG IN THE FORECAST ACROSS THE AREA.
MID WEEK INTO THE WEEKEND - MILDER TEMPERATURES WITH GROWING
CHANCE FOR FOG, DRIZZLE, AND RAIN.
UPPER AIR PATTERN ACROSS THE CONUS GETS MESSY FOR MOST OF THIS WEEK
WITH LOTS OF SHORT WAVE TROUGHS PASSING THROUGH FLOW, NONE OF WHICH
LOOK OVERLY STRONG. HOW THEY MIGRATE AND POSSIBLY MERGE MAKES FOR
SOME COMPLICATIONS BUT OVERALL NO LARGER IMPACTS TO TRAVEL IN THE
OFFING. ENSEMBLES SHOW A STRONG SIGNAL FOR LONG STREAK OF CLOUDINESS
THOUGH, THAT IS FOR SURE.
BY CHRISTMAS, WITH ONE WAVE PASSING BY TO THE SOUTH, WE WILL BE
WATCHING A BIT STRONGER OF A WAVE MOVING OUT OF THE DESERT SOUTHWEST
INTO THE SOUTHERN PLAINS. MOST ENSEMBLE MEMBERS AND BLENDS SUGGEST A
DECENT MOISTURE SOURCE AHEAD OF THIS WITH A TREND TOWARDS A WET
FINISH TO THE WEEK. PERHAPS THE GOOD NEWS, UNLESS YOU ARE A SNOW
LOVER, IS THE RISING HEIGHTS AND ABNORMALLY MILD AIR ADVECTING INTO
THE AREA. THIS WILL BE ESPECIALLY NOTED AT NIGHT LATER THIS
WEEK WITH THE WARMER AIR AND CLOUD COVER LEADING TO LOWS SOME +2
STANDARD DEVIATIONS. OUR LOWS MIGHT BE 15 TO 20 DEGREES ABOVE
NORMAL.
THE WARMER AIR WILL PLAY A FACTOR AS SOUTHWEST FLOW AND YET ANOTHER
WAVE CROSSING THE ROCKIES LATE THURSDAY TRIES TO MERGE WITH THE WAVE
AHEAD OF IT. LIFT AND MOISTURE ADVECTION NORTHWARD COULD MEAN
PERIODS OF DRIZZLE AND FOG, WITH MAYBE SOME PLAIN OLE' RAIN GOING
INTO THE WEEKEND. IN FACT PROBABILITIES ALREADY PRETTY HIGH /70%/
THAT FAR OUT FOR WIDESPREAD RAIN. AS IT ALL DRAWS CLOSER, WE WILL
HAVE TO WATCH FOR SUBTLE TERRAIN TEMPERATURE DIFFERENCES THAT
COULD PRODUCE SHORT LIVED FREEZING AND IMPACTS TO HOLIDAY
TRAVEL. NOTHING JUMPS OUT AT THE MOMENT BUT THIS IS A TRICKY
TIME OF YEAR WHEN TEMPERATURES ARE FLIRTING WITH THE FREEZING
MARK. ALSO SOME HINTS OF A DEFORMATION ZONE AS NEWLY EMERGENT
TROUGH PASSES SATURDAY NIGHT AND IF AIR IS COLD ENOUGH, COULD
SEE SOME MINOR ACCUMULATIONS ACROSS NORTHERN HALF OF AREA.
SUNDAY INTO NEXT WEEK - TURNING COLDER WITH LOWER THAN NORMAL
PRECIPITATION PREDICTABILITY
FROM THE WEEKEND ON MODEL DIFFERENCES REALLY AMPLIFY WITH CLUSTER
ANALYSIS LEADING TO WIDE VARIABILITY AND HENCE, LOWER CONFIDENCE. IT
SEEMS LIKE MOST ENSEMBLE MEMBERS HINT AT A COOLER STRETCH WITH A
MEAN UPPER TROUGH ESTABLISHING ITSELF ACROSS THE MIDDLE CONUS TO
START THE NEW YEAR. AT FIRST GLANCE THIS COLDER PUSH MIGHT MAKE
FOR A MORE SOUTHERN STORM TRACK AND NOTHING OF SIGNIFICANCE FOR
OUR AREA.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 1046 PM CST MON DEC 23 2024
MAIN TAF CONCERNS ARE MVFR/IFR CONDITIONS AT BOTH RST/LSE TAF SITES
THROUGH THE TAF PERIOD. WEAK LOW PRESSURE OVER THE GREAT LAKES
REGION WILL CONTINUE TO SPREAD STRATUS DECK OF CLOUDS OVER THE
REGION. WITH LOW LEVEL MOISTURE NEAR THE SURFACE...CEILINGS
WILL LOWER INTO IFR AT RST TAF SITE FOR A PERIOD AFTER 10Z
TUESDAY. WITH DAYTIME HEATING CEILINGS ARE EXPECTED TO IMPROVE
TO MVFR AFTER 18Z TUESDAY. THEN LOWER INTO IFR CONDITIONS
TUESDAY EVENING. SOME PATCHY FOG WILL FORM ACROSS THE AREA AS
THE LATEST HI- RESOLUTION MODELS CONTINUE TO SUGGEST VISIBILITY
COULD BE REDUCED TO IFR. HOWEVER CONFIDENCE IS LOW VISIBILITY
WILL BE REDUCED TO LESS THAN 2 MILES AND WILL CONTINUE WITH A
PERIOD OF 3 MILE VISIBILITY AT RST TAF SITE. WIND SPEEDS WILL
REMAIN LESS THAN 10 KNOTS THROUGH THE TAF PERIOD.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...FERGUSON/SHEA
AVIATION...DTJ
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