Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 212324
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
524 PM CST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 256 PM CST SUN DEC 21 2014

CHALLENGES ABOUND WITH UPCOMING WINTER STORM TONIGHT THROUGH
CHRISTMAS EVE...WITH PRIMARY CONCERNS BEING PRECIPITATION TYPE
AND AMOUNTS. SURFACE LOW TRACK AND TIMING FROM 21.12Z MODEL SUITE
IN REASONABLE AGREEMENT AND WITH FAIRLY SIMILAR THERMAL/MASS
PROFILES...WILL USE A BLENDED SOLUTION THAT MATCHES WELL WITH
LATEST WPC SNOW AMOUNTS.

FOR TONIGHT...LIGHT PRECIPITATION CURRENTLY ACROSS THE UPPER
MISSISSIPPI RIVER VALLEY WILL CONTINUE TO LIFT NORTHEAST UNDER
WEAK ISENTROPIC LIFT REGIME. EXTENDED DRIZZLE MENTION THROUGH
22.12Z AS SOUNDINGS SHOW A 3000 TO 5000 FT DRY LAYER IN THE MID-
LEVELS THAT SHOULD BE DEEP ENOUGH TO PRECLUDE THE SEEDER-FEEDER
PROCESS. ANY SNOW SHOULD BE MAINLY CONFINED TO TAYLOR/CLARK
COUNTIES WHERE SURFACE TEMPERATURES SHOULD HOVER ABOUT THE
FREEZING MARK. UP TO A HALF INCH ACCUMULATION IS POSSIBLE. ALSO
EXPECT AREAS OF FOG THROUGH THE NIGHT.

SURFACE LOW DROPS FROM SOUTHEAST SD AT 22.12Z INTO CENTRAL IOWA BY
23.12Z. WARM AIR ADVECTION/ISENTROPIC LIFT INDUCED PRECIPITATION
WILL LIFT NORTH AND EAST THROUGH THE DAY...SPREADING ACROSS THE
ENTIRE FORECAST AREA BY MONDAY AFTERNOON. MAXIMUM WEB-BULB
TEMPERATURE THROUGH THE COLUMN REMAINS WITHIN A DEGREE OF ZERO
CELSIUS ACROSS THE REGION. NEAR SURFACE TO 850 HPA LAYER
EVENTUALLY SATURATES ALONG AND JUST BELOW THE ZERO CELSIUS
ISOTHERM. WITH SURFACE TEMPERATURES GENERALLY IN THE MID 30S...
INTRODUCED PERIODS OF A RAIN/SNOW MIX THROUGH THE DAY. UNLESS
SNOWFALL RATE CAN EXCEED THE AFFECTS OF WARM SURFACE TEMPERATURES
FROM 33 TO 38 DEGREES...ACCUMULATIONS WILL BE MINIMAL...NO MORE
THAN A TENTH OR TWO. THE EXCEPTION BEING ACROSS NORTH-CENTRAL
WISCONSIN WHERE UP TO AN ADDITIONAL INCH IS POSSIBLE DUE TO COOLER
TEMPERATURES.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 256 PM CST SUN DEC 21 2014

MONDAY NIGHT THROUGH TUESDAY...THE SURFACE LOW EJECTS FROM CENTRAL
IOWA INTO THE WESTERN GREAT LAKES. WARM SURFACE TO 900 HPA LAYER
SURGES NORTHWARD ACROSS THE FORECAST AREA ALLOWING SNOW TUESDAY
MORNING TO CHANGE BACK OVER TO ALL RAIN IN THE AFTERNOON. HOWEVER...
SUB-FREEZING AIR MASS ACROSS CENTRAL MN/NORTHERN WI COULD RESULT
IN A RAIN/SNOW MIX ALONG AND NORTHWEST OF A LINE FROM MEDFORD TO
CHARLES CITY. ACCUMULATIONS TUESDAY WILL GENERALLY BE AN INCH OR
LESS IN THESE AREAS.

DRY SLOT WORKS ITS WAY INTO CENTRAL/SOUTHEAST WI TUESDAY NIGHT
INTO WEDNESDAY WITH DEFORMATION PRECIPITATION AXIS INITIALLY
ACROSS SOUTH-CENTRAL MN INTO NORTHWEST WI...THEN SLIDING ACROSS
THE FORECAST AREA WEDNESDAY NIGHT. COLUMN WILL BE COLD ENOUGH FOR
ALL SNOW...BUT MODELS SUGGEST HIGHEST QPF WILL FALL JUST NORTH
AND WEST OF THE FORECAST AREA. ADDITIONAL ACCUMULATIONS OF A FEW
TENTHS OF AN INCH POSSIBLE THROUGH WEDNESDAY REGION-WIDE.

FOR MONDAY THROUGH CHRISTMAS EVE...EXPECT SNOW AMOUNTS FROM 2 TO 4
INCHES ACROSS TAYLOR/CLARK COUNTIES...1 TO 2 INCHES ACROSS SOUTHEAST
MN INTO PORTIONS OF WESTERN WI AND LESS THAN AN INCH ACROSS
NORTHEAST IA INTO SOUTHWEST WI. THERMAL PROFILES DO NOT SUPPORT
FREEZING RAIN OR SLEET THROUGH THE EVENT.DESPITE LOWER SNOW
AMOUNTS...ROADS LIKELY TO BE SLICK AT TIMES THROUGHOUT THE PERIOD
SO PERSONS WITH HOLIDAY TRAVEL PLANS SHOULD PAY CLOSE ATTENTION TO
THE LATEST WEATHER FORECASTS AND ROAD CONDITIONS.

CHRISTMAS DAY WILL BE MOSTLY CLOUDY BUT DRY WITH TEMPERATURES
RISING INTO THE MID 30S. CHRISTMAS NIGHT THROUGH FRIDAY...THERE IS
A CHANCE FOR ADDITIONAL SNOWFALL AS ANOTHER SURFACE LOW/WAVE ALOFT
SLICES THROUGH THE UPPER MIDWEST. THE UPCOMING WEEKEND WILL BE
DRY...BUT MUCH COLDER IN THE WAKE OF A STRONG COLD FRONT.
TEMPERATURES EACH DAY WILL ONLY RISE INTO THE TEENS TO LOWER 20S
WITH NIGHTTIME LOWS IN THE SINGLE DIGITS TO LOWER TEENS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 524 PM CST SUN DEC 21 2014

BREEZY SOUTHERLY FLOW...EXPECTED TO PERSIST THROUGH MONDAY WITH A
BACKING TOWARDS MORE EASTERLY LATE...CONTINUES TO BRING MORE AND
MORE MOISTURE INTO THE TAF SITES. THUS WE SHOULD SEE THE STRATUS
PERSIST. HOWEVER...HIGHER CEILINGS AND VISIBILITIES...MAINLY IN
THE MVFR RANGE...ARE PRESENT ACROSS EASTERN IOWA. THEREFORE...
HAVE TRENDED THE VISIBILITY FORECAST MORE OPTOMISTIC...ONLY
DROPPING TO IFR BETWEEN 06-15Z AT RST AND HOLDING AT MVFR AT LSE.
CEILINGS TOO COULD END UP MORE OPTOMISTIC...BUT A COLD GROUND AND
UPSLOPE FLOW AT RST MAY KEEP CEILINGS IN THE IFR/LIFR RANGE. THE
VALLEY SITE OF LSE PLUS MIXING FROM THE BREEZE SHOULD LIMIT THE
FALL TO PERHAPS IFR FROM NIGHTTIME COOLING LATE TONIGHT. CEILINGS
SHOULD RETURN TO MVFR AT LSE BY LATE MORNING.

ONLY OTHER ITEM TO NOTE IS ON PRECIPITATION TYPE. MOST OF THE
PRECIPITATION THROUGH MONDAY IS EXPECTED AS RAIN OR DRIZZLE.
HOWEVER...LATE MONDAY THERE IS A CHANCE THE PRECIPITATION COULD
SWITCH OVER TO SNOW AT RST. IF THIS OCCURS...VISIBILITIES OF IFR
ARE POSSIBLE.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...ROGERS
LONG TERM...ROGERS
AVIATION...AJ


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