NW MONTANA GCAC BACKCOUNTRY AVALANCHE INFORMATION 2-02-01

This is Stan Bones with backcountry avalanche information for the Glacier
Park and Flathead and Kootenai National Forest areas issued at 9:30 AM,
Friday, February 2nd, 2001, by Northwestern Montana's Glacier Country
Avalanche Center.

This message does not apply to developed ski areas and is brought to you in
part by financial grants and support from:

    --The Izaak Walton Inn located at Essex
    --Kalispell Regional Medical Center
    --Rocky Mtn. Outfitter, 135 Main Street, Kalispell.
    --The Sportsman and Ski Haus in both Kalispell and Whitefish
    --Winter Sports, Inc. on The Big Mountain
    --The Aero Inn, Highway 93 South, Kalispell
    --Burlington Northern Santa Fe Railroad
    --The Flathead Nordic Ski Patrol
    --The Montana Department of Fish, Wildlife, and Parks
    --The National Forest Foundation
    --The Users and Supporters of the Glacier Country Avalanche Center

We thank Matt for his snow observations from the Jewel Basin area near Big
Fork on Thursday. 
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We are expecting a dramatic weather change on Friday.  Heavy new snowfall
accompanied by very strong W'erly winds have the potential of producing
high avalanche danger Friday and this weekend.  Both natural and human
triggered avalanches are likely.  Backcountry travelers need to be alert
that the snow instability may change rapidly and dramatically.

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WEATHER ANALYSIS
Since Monday the mountains over Northwestern Montana have received a bit of
new snow.  Most of the new was concentrated on Tuesday when many mountain
sites picked up nearly 0.5" of snow water equivalent.  North Jocko at the
southern end of the Mission Range won the big prize when it received 1.2"
SWE Tuesday.  Snowfall continued on Wednesday around Flathead Lake and
along the southern edge of our region.  The northern Swan Range and
locations in the central and southern Mission Range received another 0.5"
SWE on Wednesday.

Air temperatures over the period have generally been on the increase.
Highs on Monday and Tuesday were mostly in the mid 20's with lows in the
upper teens.  By Thursday these had warmed with the mountain daytime highs
being in the lower 30's and nighttime lows in the mid to upper 20's F.

W'erly winds have been strong almost all week, along and east of the
Continental Divide.  West of the Divide the winds have generally been light.

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SNOWPACK ANALYSIS
Our field observations this week and on Thursday were on Norman Mountain in
the northern Cabinet Range, at Noisy Basin near Big Fork, at Marias Pass
and in the Many Glacier Valley on the southern and eastern edges of Glacier
Park.  We had an additional report from the Jewel Basin area in the north
Swan.

Our backcountry tours and snowpit investigations are finding that the
snowpack is generally warming.  This is providing an increasing amount of
settling, but the rate of strengthening is slow.  We are finding a variety
of weaknesses generally concentrated in the upper half of the snow cover.
These near surface weaknesses are often associated with buried surface hoar
layers and with buried melt-freeze ice crusts.  At the base of the snowpack
we continue to see weaknesses existing in the old faceted grain layer at
the ground surface.  This layer is now insulated from the colder air
temperatures and is being compressed by the weight of overlying snow.  From
this it is gaining strength, but it is at a very slow rate.  The faceted
grains are large and persistent.

Wind loading along and east of the Continental Divide has been occurring
this week.  The potential for cohesive wind slabs existing over less dense
and more weakly bonded snow is high along and east of the Continetal
Divide.  Warming temperatures will be adding to the stress on these buried
layers.

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AVALANCHE - INSTABILITY DESCRIPTION
As of Thursday night we were finding that below 5500' in elevation we still
had a generally stable snowpack with only isolated areas of instability.
Natural avalanches were very unlikely there, while human triggered
avalanches were unlikely.  A shallow snow cover coupled with abundant
anchors generally made backcountry travel safe.  Normal caution however was
still advised.

Above 5500' a higher level of instability existed.  Unstable slab layers
associated with wind loading and with buried surface hoar and ice layers
remained possible on steep, open slopes.  Natural avalanches were unlikely,
but human triggered avalanches were possible.

Both of these levels of instability are subject to change on Friday and
that change could be rapid and dramatic.

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WEATHER FORECAST & AVALANCHE OUTLOOK
The weather forecast for Friday and this weekend is a dramatic one.  A
winter storm warning has been issued for Friday and Friday night above
4000' in
elevation.  A major Pacific storm system accompanied by a strong jet stream
is expected to push into Northwestern Montana on Friday.  Snow should begin
falling around mid morning Friday and continue into Friday evening.  Heavy
snowfall and strong westerly winds should produce blizzard-like conditions,
especially in the mountains on west facing slopes.  The heavy snowfall is
forecasted to decrease to orographic snow showers by Friday night and
Saturday.  Strong jet stream energy however, is expected to remain over the
region through Saturday, still imparting breezy conditions.

The freezing levels Friday through Sunday are forecasted to remain at or
near the valley floors.  We are expecting 6-12" of new snowfall in the
mountains Friday with 3-6" possible in the valleys.  The new snowfall 
should diminish to less than 3" on Saturday and only a trace on Sunday.

Daytime high temperatures should be in the lower to mid 20's in the
mountains each day.  Winds are expected to be very robust during the
period, blowing mostly from the west.  We are likely to experience W'erly 
winds Friday at the ridge and mountain top levels blowing between 35-45 MPH.  
These should drop by 10 Saturday to 25-35 MPH and diminish another 5 MPH on 
Sunday to 20-30, still from the W.

These conditions of heavy new snowfall accompanied by very strong winds
should guarantee a dramatic increase in the avalanche danger this weekend.
Backcountry travlers should be alert for rapidly increasing snow
instability, particularly on Friday.  We expect to see both natural and
human triggered avalanches occurring this weekend.

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This concludes the current avalanche message.  The next regularly scheduled
update will be issued by 9:30 AM, Tuesday, February 6th, 2001.

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This message best describes conditions at the time of its issuance.  As
time passes avalanche and snow conditions may change, sometimes quite
rapidly.  Elevation and geographic distinctions used are approximate and a
transition zone between hazards exist.  Because of the general nature of
the message, each backcountry party will always need to make their own site
and time specific avalanche hazard evaluations.

Thank you again for your continuing support of Northwestern Montana's
Glacier Country Avalanche Center.

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