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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, January 5th, 2013 - 7:00AM
Expires
Sun, January 6th, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Recent avalanche activity tells us that the mountains are still reactive in a deep and dangerous way.   Above treeline we can expect CONSIDERABLE avalanche danger.   Natural avalanches are still possible, but human triggered avalanches are the bigger concern.   With the deep slab problem we don’t expect a lot of avalanches to happen, but those that do will be large and destructive.   Below treeline, watch for large runouts hanging above and continue to treat every steep slope with respect.

Special Announcements

Chugach Electric is doing a major overhaul of the powerlines from Ingram creek to Silvertip across Turnagain Pass.   The entire powerline easement is a construction zone this winter.   We can expect heavy equipment in the corridor and stashed materials such as culverts and poles which may be partially buried by snow.   Caution is needed while traveling in the powerline easement.

Sat, January 5th, 2013
Alpine
Above 2,500'
3 - Considerable
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
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

Recent avalanche activity is the most pertinent information we have available, and it’s telling us a compelling story right now.  Yesterday we had a new avalanche on the north end of the motorized side of Turnagain Pass, with wide propagation on an east facing slope.  Around 850 in the morning yesterday the large avalanche path between Portage lake and the Whittier tunnel entrance slid full width and full depth.  On Wednesday a large avalanche was triggered on Tincan by a skier, then we got another foot of snow.  If you haven’t watched the video by Alyeska ski patrol yet, it’s worth taking a few minutes to see their perspective of managing the same deep slab problem at the ski area.

Our weak layer is now buried 3-10 feet deep, depending on wind loading.  It is difficult for a single person to affect something that deep, but if a collapse is initiated from a shallow trigger point the resulting avalanche is likely to be very large.  A skier should be concerned about trigger points in steeper terrain, including near exposed rocks, sparse trees, or on the edge of a wind scoured ridge.  Snowmachines cause a greater force on the snow and will be more likely to be a deep slab trigger.  Slope angles above 35 degrees deserve extra caution and avoidance, and every aspect is affected.

Common tools to identify avalanche hazard with this deep slab problem are not likely to be effective.  Don’t expect to see shooting cracks or hear whoomphing, because that weak layer is buried deeper than your ski pole.  Test slopes will also not show an unstable character unless they break full depth, which is what we’re trying to avoid in the first place.   Compression tests on isolated snow columns may indicate false stable results.  All this information is superseded by evidence of natural avalanche activity and a weak layer which we know is not gaining strength quickly.

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

Forecasted wind is enough to create fresh wind slabs.  We have yet to notice a problem within the storm layers of the last 12 days, but that’s mainly because few people have ventured above 2500 feet.  Wind slabs are a concern of their own, but combined with a deep slab step down potential they can be extra dangerous. 

Weather
Sat, January 5th, 2013

Little to no precipitation in the last 24 hours and moderate wind has not added much to the avalanche problem.   Today 2-6 inches of snow is expected with strong southeast wind at the ridges.   Slightly colder temperatures are expected to keep the snow line down to sea level.  

In the long term, a chance of snow is in the forecast every day for the next 4 days.   We will stay in the active pattern into next week, but not as intense as we’ve seen recently.


Wendy will issue the next advisory on Sunday, January 6th.

Observations
Recent Observations for Turnagain Pass
Date Region Location
02/20/24 Turnagain Avalanche: Tincan
02/19/24 Turnagain Avalanche: Base of Seattle Ridge
02/18/24 Turnagain Observation: Lynx creek
02/18/24 Turnagain Observation: Tincan Trees
02/17/24 Turnagain Observation: Turnagain (below the uptrack)
02/15/24 Turnagain Observation: Sunburst
02/13/24 Turnagain Observation: Tincan Backdoor, Center Ridge
02/12/24 Turnagain Avalanche: Tincan Trees
02/11/24 Turnagain Observation: Cornbiscuit
02/10/24 Turnagain Observation: Tincan
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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.