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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, December 5th, 2012 - 7:00AM
Expires
Thu, December 6th, 2012 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Cold and stable weather persists, holding the avalanche problem steady over the last 2 weeks.  Above treeline, pockets of Moderate avalanche danger may still be found, but the trend is for slowly diminishing problems.  It’s been a while now since we’ve seen any new significant avalanche activity.

Wed, December 5th, 2012
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

A shallow faceted snowpack and little wind keeps the danger trend the same.  In most places people are traveling the snowpack has rotted out to a sugary, sometimes unsupportable base.  Collapses or whumphing are getting harder to find, and seem to be focused closer to a person than they were a couple weeks ago.  Pit tests are confirming this trend with poor propagation potential compared to mid November.  The nature of the snowpack makes it hard to explore too far without hitting rocks…  If you are going skiing, you might want to grab some p-tex repair materials on the way home.

A healthy amount of uncertainty still exists in the mountains.  We know the structure of the snowpack is poor.  Very few people are testing slopes steeper than 35 degrees.  Our information is limited due to below average use because of the difficulty in accessing much of our backcountry terrain.  While it seems unlikely to trigger a major avalanche, anything that does slide will strip the snow to the ground, exposing rocks and other trauma inducing objects at the bedsurface.  A Moderate level of caution is still warranted in the steeper zones above treeline.  

Weather
Wed, December 5th, 2012

It is cold and calm outside today.  The temperature inversion continues with Portage reading -23 this morning and ridgetops around Girdwood and Turnagain Pass reaching into the low teens.  

The general weather trend is expected to hold until the weekend, then snow is possible with temperatures rising to the 20s.  According to NOAA –  PATTERN CHANGE STILL UPCOMING USHERING IN A MORE PROGRESSIVE SOUTHWESTERLY FLOW AFTER THE WEEKEND…HOWEVER THE DETAILS ARE STILL UP IN THE AIR ON EXACTLY WHERE THE PREDOMINANT STORM TRACK WILL SET UP.


This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).  

Wendy will issue the next advisory Thursday morning, December 6th.

Observations
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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.