Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 222045
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
245 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 OLWEIN TO LA CROSSE TO WASSAU. 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 18Z TAFS THROUGH 18Z TUESDAY MORNING)
ISSUED AT 1133 AM CST MON DEC 22 2014

SOUTHEAST LOW LEVEL FLOW WAS PULLING SOME DRIER SFC-925MB AIR INTO
THE AREA LATE THIS MORNING...WITH CIGS RISING TO VFR ALONG/EAST OF A
KOLZ-KONA LINE. THIS SHOULD WORK INTO THE KRST AREA WITH AT LEAST
MVFR CIGS FOR A WHILE THIS AFTERNOON. HAVE TRENDED TAFS FOR VFR/MVFR
CIGS THIS AFTERNOON. BROAD AREA OF PRECIP WAS LIFTING NORTH ACROSS
IA LATE THIS MORNING. THIS WILL SPREAD ACROSS THE TAF SITES FOR THIS
AFTERNOON/EVENING...WITH MAINLY MVFR/VFR VSBYS IN -RA/BR. COLUMN
COOL ENOUGH FOR SOME -RASN MIX IN THE KRST AREA. BIT OF A LULL IN THE
PRECIP ROUGHLY 03Z-09Z...BUT THE SFC LOW WILL BE APPROACHING WITH
INCREASING MOISTURE/LIFT. CIGS/VSBYS GO BACK TO MFVR/IFR TONIGHT...
WITH ANOTHER BAND OF PRECIP LIFTING NORTH ACROSS SOUTHEAST MN/
WESTERN WI LATE TONIGHT/TUE MORNING. LIFT AND COOLING ALOFT EXPECTED
TO CHANGE PRECIP IN THIS BAND TO ALL -SN AT KRST AFTER 06Z AND AT
KLSE AFTER 13Z. ACCUMULATIONS IMPACTING AIRPORT OPS EXPECTED AT KRST
LATE TONIGHT/TUE MORNING...WITH PERHAPS A SLUSHY INCH OR TWO 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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