Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 222338
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
538 PM CST MON DEC 22 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 245 PM CST MON DEC 22 2014

CHALLENGES CONTINUE WITH THE WINTER STORM THIS EVENING THROUGH
TUESDAY...NAMELY PRECIPITATION TYPE AND SNOW AMOUNTS. 22.12Z MODEL
SUITE MASS FIELDS IN GOOD OVERALL AGREEMENT THROUGH THE EVENT.
HOWEVER...MINOR DIFFERENCES IN THE THERMAL PROFILES...COMPOUNDED
BY THE FACT THAT SOUNDINGS WOBBLE ABOUT THE ZERO DEGREE ISOTHERM
MAKE PRECIPITATION TYPE PARTICULARLY DIFFICULT. ALL SAID...THERE
HAS STILL BEEN A SOUTHERN TREND IN THE TRACK OF THE SURFACE LOW AS
IT BRIEFLY DIPS INTO NORTHERN MO THIS EVENING BEFORE EJECTING
NORTHEASTWARD ACROSS SOUTHERN WI ON TUESDAY. THIS ALLOWS THE
PRIMARY DEFORMATION AXIS TO SET-UP ACROSS THE NORTHWEST THIRD OF
THE FORECAST AREA AND ENHANCES THE CHANCE FOR ACCUMULATING
SNOWFALL PRIMARILY ON TUESDAY.

FOR THIS EVENING...FIRST WAVE OF PRECIPITATION WILL LIFT ACROSS
THE FORECAST AREA. THERMAL PROFILES ARE WARM ENOUGH FOR MOSTLY
RAIN...EXCEPT ACROSS TAYLOR/CLARK COUNTIES WHERE SOME ACCUMULATING
SNOW (LESS THAN AN INCH) IS POSSIBLE. TEMPERATURES WILL CHANGE
VERY LITTLE AND REMAIN IN THE MID TO UPPER 30S.

FOR TONIGHT...LOW-MID LEVEL WARM FRONT WILL SURGE NORTHWARD AS
SURFACE LOW MOVES INTO NORTHEAST IA. A SECONDARY WAVE OF
PRECIPITATION WILL SWEEP ACROSS THE FORECAST AREA FROM SOUTH TO
NORTH ALONG AXIS OF STRONG WARM AIR ADVECTION AND ISENTROPIC LIFT.
IN GENERAL...EXPECT A NARROW CORRIDOR OF A RAIN SNOW MIX NEAR THE
TRACK OF THE SURFACE LOW WITH SNOW TO THE NORTHWEST AND RAIN TO
THE SOUTHEAST. MODELS ARE HINTING AT A 925 TO 850 HPA WARM TONGUE
TO WRAP AROUND THE LOW BY TUESDAY MORNING...BUT ITS IMPACT ON
PRECIPITATION TYPE SHOULD BE FELT MAINLY FOR AREAS THAT WILL
ALREADY BE SEEING RAIN.

ACCUMULATING SNOW IS MAINLY A CONCERN ON TUESDAY WEST OF A LINE
FROM OELWEIN TO LA CROSSE TO WAUSAU. EXPECT RAIN OR A RAIN/SNOW MIX
FARTHER SOUTH AND EAST. WARM AIR THIS EVENING AND A SLOW
TRANSITION TO A COLDER AIR MASS MAY INITIALLY LIMIT SNOWFALL...
BUT MODELS SHOW ALL BUT THE NEAR SURFACE LAYER DROPPING BELOW
FREEZING BY 23.12Z. EXPECT STRONG LIFT FROM 5 TO 8 UBAR/SECOND
ALONG THE -15 C ISOTHERM WITHIN DEFORMATION SNOW AXIS TO GENERATE
SNOWFALL RATES HIGH ENOUGH TO OVERCOME WARM SURFACE TEMPERATURES
AND ACCUMULATE. NEW FORECAST CALLS FOR 1-3 INCHES OF HEAVY WET
SNOW ACROSS PORTIONS OF NORTHEAST IA/SOUTHEAST MN/WESTERN WI WITH
THE HIGHEST AMOUNTS ACROSS ELEVATED TERRAIN. THIS MATCHES FAIRLY
WELL WITH LATEST GFS/NAM COBB OUTPUT AND SREF PLUMES. ACCUMULATING
SNOWFALL WILL BE BEST REALIZED ACROSS GRASSY SURFACES...BUT COULD
STILL SEE SLUSH ACCUMULATIONS ON UNTREATED ROADWAYS MAKING TRAVEL
DIFFICULT...ESPECIALLY DURING THE TUESDAY MORNING COMMUTE. WILL
KEEP CURRENT WINTER WEATHER ADVISORY FOR TAYLOR COUNTY AND MONITOR
ALL OTHER AREAS FOR POSSIBLE EXPANSION. SEE SPS FOR ADDITIONAL
INFORMATION.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 245 PM CST MON DEC 22 2014

PRECIPITATION WILL DISSIPATE TUESDAY NIGHT WITH ONLY SOME
LINGERING LIGHT SNOW POSSIBLE ON CHRISTMAS EVE DAY. TEMPERATURES
WILL REMAIN IN THE MID 30S. CHRISTMAS DAY WILL BE DRY WITH LITTLE
CHANGE IN TEMPERATURE AS A BROAD SURFACE RIDGE SLIDES ACROSS THE
UPPER MISSISSIPPI RIVER VALLEY.

SNOW CHANCES INCREASE THURSDAY NIGHT THROUGH FRIDAY AS THE NEXT
TROUGH CARVES ITS WAY ACROSS THE WESTERN CONUS. SURFACE LOW TRACK
IS SIMILAR BETWEEN THE 22.12Z GFS/ECMWF/GEM...BUT PRECIPITATION
PLACEMENT DIFFERS BETWEEN THE DRIER ECMWF AND WETTER GFS/GEM. FOR
NOW...WILL FOLLOW SUPERBLEND GUIDANCE AND BROAD BRUSH CHANCE POPS
ACROSS THE FORECAST AREA.

AFTER A COLD FRONT SWEEPS ACROSS THE REGION FRIDAY NIGHT...THE
UPCOMING WEEKEND LOOKS DRY BUT COLDER WITH DAILY HIGH TEMPERATURES
IN THE 20S AND NIGHTTIME LOWS MAINLY IN THE TEENS. THERE IS A
SLIGHT CHANCE FOR SNOW SUNDAY NIGHT INTO MONDAY...BUT GIVEN VAST
MODEL DIFFERENCES...WILL KEEP 20 POPS AT THIS TIME.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 538 PM CST MON DEC 22 2014

ONE BAND OF -RA OR -RA/-SN WAS LIFTING NORTH ACROSS THE TAF SITES
LATE THIS AFTERNOON/EARLY THIS EVENING. THIS BAND TO LIFT NORTH OF
THE TAF SITES BY 02Z. BULK OF VSBY RESTRICTION DURING THE MID
EVENING TO EARLY OVERNIGHT HOURS DUE TO BR AND SOME -DZ AS MOIST AIR
IS ADVECTED OVER THE COLD GROUND. CIGS TO REMAIN MVFR/IFR TONIGHT. A
SECOND BAND OF -RA/-SN WILL DEVELOP OVER MO/IA THIS EVENING...THEN
LIFT NORTH INTO/ACROSS THE TAF SITES MAINLY 09-18Z TUE. AS THE
AIRMASS COOLS LATE TONIGHT...PRECIP IN THIS BAND EXPECTED TO SWITCH
TO ALL SNOW. PRESENT TIMING WOULD PUT THE SWITCH TO ALL SNOW AROUND
06Z AT KRST...WITH THE HEAVIER SNOW FALLING BETWEEN 09-18Z AS THE
BAND PIVOTS ACROSS THE AREA. A LITTLE TRICKER IN THE MS RIVER VALLEY
AT KLSE. PRECIP NOT EXPECTED TO SWITCH TO SNOW AT KLSE ON THE MS
VALLEY FLOOR UNTIL NEAR/AFTER 12Z WHEN THE HEAVIER PORTION OF THE
BAND WOULD MOVE IN. WITH SOME DIURNAL WARMING...-SN TO MIX WITH -RA
FOR THE AFTERNOON OR BECOME LIGHTER AS AS THE MAIN PRECIP BAND LIFTS
NORTH OF THE TAF SITES. IFR/MVFR CIGS/VSBYS TO PERSIST THRU TUE. 2
TO 3 INCHES OF SNOW IMPACTING AIRPORT OPS EXPECTED AT KRST LATE
TONIGHT/TUE MORNING...WITH PERHAPS A SLUSHY INCH OR SO AT KLSE TUE
MORNING.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR WIZ017.

MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...ROGERS
LONG TERM...ROGERS
AVIATION.....RRS


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