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Thu, January 14th, 2016 - 7:00AM
Fri, January 15th, 2016 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

Today a  MODERATE  avalanche danger exists at and above Treeline where cornices should be avoided and lingering wind slabs are possible in steep terrain.  At Treeline, glide crack movement has been active including several that have avalanched to the ground over the last few days. These unpredictable hazards can release unexpectedly and should be avoided. Today’s avalanche concerns require you to be aware of what is above and below you and avoid specific high consequence hazards.

Below Treeline the danger is  LOW  where triggering an avalanche is unlikely.

Yesterday buried surface hoar was found in Lynx creek where a shallower snowpack exists. Similar to Summit Lake, more caution and careful snowpack evaluation is essential on the Southern side of our forecast zone. See the most recent  Summit Lake Summary  for  snowpack observations.  

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Thu, January 14th, 2016
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
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. Dangerous avalanche conditions. 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
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Yesterday’s poor visibility made it challenging to see this unpredictable hazard. We received a report of a glide release on Seattle Ridge yesterday, but the exact location is unknown at this point. Glide cracks are appearing all over Turnagain Pass between 1000’ to 2500’ and are showing up in popular areas. Monitoring their movement is helpful, but there is no discernable pattern to predict a failure as they tend to fail naturally and on their own schedule. Warm temperatures can trigger them and so can cooling temperatures. Cracks can form and release in seconds or days later or sometimes a glide crack won’t release at all, and benignly just fill back in with snow.

Glide cracks are best to be given a wide berth.  Limit your exposure time spent underneath and if skiing or riding in terrain with glide cracks, try and map them out before your travels so as not to end up directly on top of or inside one.  Remember, when these do fail, they tend to be destructive, failing to the ground bringing the entirety of the snowpack with them.  

Along Seattle Ridge glide cracks are becoming more abundant in specific locations. Avoidance of these unpredictable harzards is key. Thanks for the photo and observation Travis!


Avalanche Problem 2
  • Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices have grown considerably during the past few weeks. Not only do they have the potential to fall naturally, but also to be triggered by the weight of a person or snowmachine. They can also trigger an avalanche on the slope below when they fall. Travel under or on them should be avoided. Today’s weather forecast should make travel into the Alpine easier with good visiblity, thus don’t forget cornices have the tendency to break farther back from the ridge than expected.   

Additional Concern
  • 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

As we move further away from our most recent storm event that ended on Jan.11 wind slabs are becoming a low likelihood concern. However triggering a lingering wind slab could have high consequences in places with cliffs, rocks, or trees below. Obvious signs like shooting cracks may not be present until its too late, as wind slabs are known for breaking above you, once you are well onto a slab. Ease into steep terrain and avoid terrain features with high consequences.

*Yesterday we received a report of buried surface hoar found in a snow pit in Lynx Creek.  This weak layer is more suspect in protected areas of the snowpack, but could be more widespread in this region. Similar to Summit Lake areas, Johnson Pass and Lynx Creek have a shallower snowpack where conservative terrain choices should be utilized. 

Thu, January 14th, 2016

Yesterday light snow fell in Girdwood and Turnagain Pass leaving trees with over an inch of white stuff. Valley fog was also observed. Winds were clam from the East and temperatures remained just below freezing, <30F.

Today skies are expected to be mostly sunny becoming partly cloudy by mid afternoon. Patches of Valley fog could obscure visibility at lower elevations with a chance of light snow in the afternoon.  Temperatures will be in the mid 20F’s today. Expect light ridgetop winds from the East.

*Wind data from Sunburst Weather Station is from 2pm to 6am, due to a rimed anemometer  that is now fixed.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  26 trace   0   84  
Summit Lake (1400′) 28   trace    0 27  
Alyeska Mid (1700′) 27   2   .17   63  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25   *E   *3   *13  
Seattle Ridge (2400′)  25 n/a    n/a   n/a    
Recent Observations for Turnagain Pass
Date Region Location
11/16/23 Turnagain Observation: Tincan Common
11/14/23 Turnagain Observation: Sunburst/Magnum
11/14/23 Turnagain Observation: Seattle Ridge
11/13/23 Turnagain Avalanche: Tincan Trees
11/12/23 Turnagain Observation: Sunburst
11/12/23 Turnagain Avalanche: Goldpan – avalanche
11/11/23 Turnagain Observation: Tincan Common
11/11/23 Turnagain Observation: Taylor Pass – Sunburst
11/10/23 Turnagain Observation: Tincan
11/10/23 Turnagain Observation: Tincan Trees
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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.