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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, January 10th, 2016 - 7:00AM
Expires
Mon, January 11th, 2016 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

A CONSIDERABLE avalanche danger exists in the Alpine where wind slabs 1-2′ thick are possible on steep windloaded features. Careful snowpack evaluation and cautious routefinding are recommended in places where winds are actively loading slopes. The avalanche danger at and below Treeline is MODERATE where rain saturated the snowpack yesterday and triggering a wet loose avalanche in a terrain trap will be difficult to escape. Wet snow will be more likely in Girdwood where more rain and lower elevation terrain exists.

In areas such as  Summit Lake, the snowpack is shallower and harbors more weak layers. Click HERE to read yesterday’s Summit Lake Summary.  

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Sun, January 10th, 2016
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
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

In Turnagain Pass storm snow instabilities due to recent snow, rain and active wind loading are today’s primary concerns. 

Wind Slabs – Today Easterly ridgetop winds are expected to be in the 30-40’s mph for the second day in a row with an additional 3-5” of new snow. This means avalanches will be composed of the new storm snow from the last two days and are not expected to break into layers deeper in the pack. Isolated windslabs 1-2’ deep are possible on windloaded features. This problem is manageable by avoiding slope angles over 35° where the snow is windloaded. Pay attention for stiff hollow snow, shooting cracks, and snow being transported off of ridge tops.

Wet Loose – A saturated snow pack was observed yesterday below 1500’ causing the snow to be loose and unconsolidated. This problem is stabilizing in places where temperatures cooled enough to form a crust. Should you encounter wet saturated snow, this is an additional reason to avoid gullies and steep channeled terrain. This problem is more developed in Girdwood where more over an 1″ of rain saturated the snowpack yesterday at lower elelvations. 

Should a break in the weather today allow for easier travel remember to practice safe travel rituals. 

  • Only expose one person at time on a slope
  • Regroup in safe zones
  • Always have an escape route

Yesterday two very small natural windslabs were observerd on Southeast aspects near Johnson Pass. These crossloaded gully features are examples of terrain that could harbor tender windslabs today.

Avalanche Problem 2
  • 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

Glide cracks have been appearing throughout Turnagain Pass over the last week. Warm temperatures and rain have been adding stress to these very unpredictable hazards. Pay attention for large open cracks in the snow, ‘crevasse looking’ features that can release without any warning. Similar to managing a cornice, it is best to avoid traveling on or under slopes with glide cracks. 

Additional Concern
  • Cornice
    Cornice
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

Cornice features have grown large over the last few weeks, and todays blowing snow may be adding stress to their unstable nature. They have the potential to fall naturally or be triggered by the weight of a person or machine and can be very dangerous. Travel under or on them should be avoided. They have the tendency to break farther back from the ridge than expected. As you approach ridgelines, ensure you aren’t accidently traveling on overhanging snow. 

Weather
Sun, January 10th, 2016

Yesterday 36F temps caused rain along Turnagain Pass (1000′), and by afternoon temps cooled to 32F with scatted snow showers in the afternoon. 4-8″ of new snow fell in the upper elevations. Rain/snow line was estimated to have reached 2000′ early yesterday morning. Easterly Ridgetop winds averaged in the 30’s mph with gusts in the 60’s mph.  

Today Easterly ridgetop winds are expected to average in the 30-40’s mph.  Gust could reach into the 60’s mph. Up to 5 € of snow is expected above 1100′ today and light rain at lower elevations. Temperature should hover around freezing 32F along road level at Turngain Pass.

Expect warm temperatures, snow and rain to continue through mid-week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   4   0.4   85  
Summit Lake (1400′) 33   1   0.1   25  
Alyeska Mid (1700′) 32   10   1.22   66  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23   ENE   28   64  
Seattle Ridge (2400′) 28   n/a    n/a   n/a    
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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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