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000
FXUS63 KARX 080506
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1105 PM CST SAT DEC 7 2013

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 206 PM CST SAT DEC 7 2013

FORECAST FOCUS IS ON SNOW POTENTIAL LATE TONIGHT THROUGH SUNDAY
WITH SEVERAL INCHES OF LIGHT FLUFF ANTICIPATED TO ACCUMULATE.

20Z SURFACE ANALYSIS SHOWS ARCTIC HIGH PRESSURE ENTRENCHED ACROSS
THE CENTRAL PART OF THE COUNTRY...WITH CHILLY TEMPS AND VERY
LITTLE IN THE WAY OF CLOUD COVER. BUT THIS IS EXPECTED TO CHANGE
AS A TROUGH OUT ACROSS THE INTERMOUNTAIN WEST MOVES QUICKLY INTO
OUR AREA BY SUNDAY AFTERNOON. WITH SUCH COLD AIR IN PLACE...AS THE
RELATIVELY WARMER AND MORE MOIST AIR MOVES NORTHWARD AHEAD THE
SYSTEM...SEVERAL HOURS OF LIGHT FLUFFY SNOW WILL OCCUR. SATELLITE
SHOWS HIGH CLOUDS ALREADY STREAMING INTO IA AHEAD OF THE SYSTEM...
WITH THICKENING CLOUDS THROUGH THE NIGHT TONIGHT.

MODELS HAVE BEEN INSISTING THAT THE FIRST WAA/ISENTROPIC UPGLIDE
SNOW WILL BEGIN ACROSS WESTERN IA AND SOUTHERN MN BY 12Z...BUT IT
WILL BE FIGHTING VERY DRY AIR INITIALLY. MODEL SOUNDINGS SHOW THE
DOWNWARD SATURATION WITH TIME. FEEL LIGHT ACCUMULATION WILL BE
POSSIBLE OVER SOUTHEAST MN AND NORTH CENTRAL IA ALREADY BEFORE
SUNRISE...WITH SNOW QUICKLY OVERSPREADING THE REMAINDER OF THE
AREA DURING THE MORNING. DRY AIR WILL BE THE MOST STUBBORN OVER
SOUTHERN WI WITH THE EASTERLY FLOW AROUND THE DEPARTING SURFACE
HIGH. WITH THIS SCENARIO AND IN AN EFFORT TO COORDINATE WITH
SURROUNDING OFFICES...HAVE STAGGERED THE START TIMES OF THE WINTER
WEATHER ADVISORY. SNOW RATIO SHOULD BE IN THE 17:1 TO 20:1
RANGE...SO IT WILL NOT TAKE MUCH LIQUID TO GENERATE A GOOD DEAL OF
SNOW. SNOW SHOULD BE TAPERING OFF FROM WEST TO EAST SUNDAY NIGHT.
PROBABLY COULD END THE ADVISORY EARLIER THAN 12Z MONDAY OVER
MN/IA...BUT KEPT IT GOING FOR SIMPLICITY. ONE OTHER CONCERN IS THE
WESTERLY WINDS THAT WILL KICK IN BEHIND THE SYSTEM. WITH THE LIGHT
FLUFFY NATURE OF THE NEW SNOW...IT WILL PROBABLY BE MOVED AROUND
WITH THE WIND. DO NOT FEEL IT WILL BE TRUE BLOWING SNOW HOWEVER...
BUT RATHER JUST SOME DRIFTING IN OPEN AREAS.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 206 PM CST SAT DEC 7 2013

HIGH PRESSURE BUILDS IN AGAIN ON MONDAY...BUT THE AREA WILL REMAIN
UNDER NORTHWEST FLOW ALOFT. SEVERAL PASSING WEAK SHORT WAVE
TROUGHS IN THE FLOW MAY RESULT IN SOME LIGHT SNOW OR FLURRIES FROM
TIME TO TIME. ONE SUCH DISTURBANCE COMES THROUGH MONDAY NIGHT INTO
TUESDAY ACROSS NORTHERN WI...AND ANOTHER COMES THROUGH TUESDAY
NIGHT...AND YET ANOTHER THURSDAY AND FRIDAY. IT WILL REMAIN QUITE
CHILLY THROUGH THE COMING WEEK AS WELL...WITH TEMPERATURES
REMAINING WELL BELOW NORMAL ALL THROUGH THE WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1105 PM CST SAT DEC 7 2013

SNOW WILL FALL ACROSS KRST/KLSE SUNDAY AFTERNOON/EVENING...REDUCING
VSBYS TO 1-2SM WITH IFR/MVFR CIGS FROM 400-1200 FT. HIGHEST SNOWFALL
RATES WILL LIKELY BE IN THE LATE AFTERNOON/EVENING WHEN THE UPWARD
MOTION IS STRONGEST IN THE DENDRITIC ZONE GROWTH REGION. SOME PERIOD
OF 1/2SM SN COULD OCCUR...BUT CONFIDENCE IN WHEN NOT HIGH ENOUGH TO
INCLUDE WITHIN THE TAFS.

ANOTHER UNCERTAINTY IS WHEN THE VSBY REDUCING SNOWS MOVE IN...AND
WHEN THEY WILL LEAVE. 00Z SOUNDINGS FROM MPX/DVN SHOW A LOT OF LOW
LEVEL DRY AIR ACROSS THE REGION...WHICH NEEDS TO BE SATURATED.
INITIAL ISENTROPIC UPGLIDE WILL HELP WITH THIS...BUT THE RESULT IS
THAT ACCUMULATING MVFR/IFR SNOWS MIGHT HOLD OFF UNTIL LATER IN THE
MORNING. IN ADDITION...SOME MODELS SUGGEST THAT THIS SYSTEM COULD BE
SLOWER. STILL...MOST IMPACTFUL SNOWFALL SHOULD BE DONE BY 09-12Z
MONDAY MORNING. KRST COULD EXPERIENCE SOME BLSN MONDAY MORNING AS
WINDS INCREASE.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER WEATHER ADVISORY FROM 6 AM SUNDAY TO 6 AM CST MONDAY FOR
     WIZ017-029-032>034-041.

     WINTER WEATHER ADVISORY FROM NOON SUNDAY TO 6 AM CST MONDAY FOR
     WIZ042>044-053>055-061.

MN...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 6 AM CST MONDAY FOR
     MNZ079-086-087-094-095.

     WINTER WEATHER ADVISORY FROM 6 AM SUNDAY TO 6 AM CST MONDAY FOR
     MNZ088-096.

IA...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 6 AM CST MONDAY FOR
     IAZ008-009-018-019.

     WINTER WEATHER ADVISORY FROM 6 AM SUNDAY TO 6 AM CST MONDAY FOR
     IAZ010-011-029-030.

&&

$$

SHORT TERM...MW
LONG TERM....MW
AVIATION.....RIECK