Snow Avalanche Guidance
Issued by NWS Missoula, MT

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FWUS45 KMSO 181120
SAGMSO

Backcountry Forecast for western Montana and north central Idaho
National Weather Service Missoula MT
420 AM MST THU DEC 18 2014

...MODERATE RAIN AT TIMES ABOVE 6000 FEET ON SUNDAY...

DISCUSSION:

A series of weak storm systems will traverse the Northern Rockies
today through Saturday. Long-lasting light snow will exist across
northwest Montana and above pass elevations across the entire region
during this time. Snow addition to snow pack will be fairly
minimal.

A significant subtropical moisture surge is expected over the
Northern Rockies on Sunday. Snow levels will rapidly increase from
around 3500 feet to 6500 feet throughout the day. Periods of
moderate rain on established snowpack, particularly for north
central Idaho and west central/southwest Montana ranges, is
anticipated. Snow levels are likely to return back to the 4000
feet range by Sunday night, with relatively high density snow
accumulating over pass elevations and higher. Snow ratios will
decrease steadily following the subtropical surge and a gradually
shift to northwesterly flow aloft.

A dramatic change to arctic cold, very cold wind chill, and some
relatively low density is anticipated for the second half of next
week. Winds are likely to redistribute snow onto the west through
south facing slopes during this transition, in the Thursday
through Friday time frame. All in all, this appears to be an
extreme fluctuation in snow ratio from the beginning through the
end of the next week.

For the latest information on watches, warnings and advisories, go
to weather.gov/missoula.

&&
Elevations above 4,000 FT:

                      TODAY        TONIGHT      FRI
Cloud Cover           75%          65%          80%
Hi/Lo Temps           29 to 36     22 to 29     30 to 36
Winds(mph)            SW  9G23     SW  9G23     SW 10G23
Precip Chc            40           30           40
Precip Type           snow         snow         snow
Liquid Amt            0.05         0.02         0.07
Snow Ratio(SLR)       19:1         18:1         16:1
Snow Amt(in)          0-1          0            1-2

Snow Level            3000         3000         3500

$$


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