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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, December 21st, 2013 - 7:00AM
Expires
Sun, December 22nd, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Human triggered avalanches have been reported in the last 24 hours.  The most significant that we know of is this report from Summit.   Snowpack structure remains poor, and red flags such as whoomphing are common if you break trail.  

The danger rating is  MODERATE for persistent slab concerns, especially in areas that have a stiffer wind slab on the surface.  Natural avalanches are unlikely but human triggered avalanches are possible in steep terrain.  

Special Announcements

Happy solstice!  Our daylight hours will be GAINING from now on.

Sat, December 21st, 2013
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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

The interface that we have found most likely to fail is around the early December freezing-drizzle crust.  This layer is now buried 12-18 inches or deeper in wind loaded areas.  See this observation for a pit profile.  Every new bit of snow adds stress to those layers, but we haven’t had any large storms to overload the snowpack to widespread failure – meaning no large natural avalanche cycle.  This leaves some areas on the brink of failure, waiting for a trigger to release that energy.  A lot of people have noticed widespread whoomphing as the layers collapse when a person walks or rides on the snow.  In a few cases the slope was steep enough to avalanche when that collapse happened.  

A small amount of new snow today will add to the stress in the snowpack, but probably not enough to cause natural avalanches.  The overall avalanche problem today will be similar to the last few days.  

Photos from Tenderfoot, above Summit Lake from Friday.

Weather
Sat, December 21st, 2013

A little bit of snow fell overnight.  About 2 inches of new are on the ground as of 6am.  A moderate east wind has been steady through the night, gusting to a peak of 27 at Sunburst.  

Another 2 inches of snow is expected to fall through the day today.  Temperatures are approaching freezing, and may pass that mark at lower elevations.  A freezing rain advisory is in effect, mainly in the interior Kenai from Turnagain pass to Moose pass.  

Observations
Recent Observations for Turnagain Pass
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04/15/24 Turnagain Observation: Seward Highway – Tern Lake to Portage Joel Curtis
04/14/24 Turnagain Observation: Sunburst T. Olsen-Lund, R. Sullivan I. Adams
04/14/24 Turnagain Observation: Turnagain Pass Snomo K. Gallaher
04/13/24 Turnagain Observation: Spokane Creek Everet Megli
04/11/24 Turnagain Observation: Tincan John Sykes Forecaster
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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.
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