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Thu, March 23rd, 2017 - 7:00AM
Fri, March 24th, 2017 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger is MODERATE on slopes steeper than 35 degrees and at all elevations. Human triggered slab avalanches 1-2+’ thick are possible in areas that saw a foot or more of new snow from over the weekend. Triggering fast moving loose snow €˜sluffs’ will also be possible in steeper terrain. There are a few glide cracks out there, limit time underneath them and give cornices a wide berth.

Summit Lake:  Read the  Saturday Summit Summary  HERE.  

Thu, March 23rd, 2017
Above 2,500'
2 - Moderate
Avalanche risk
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

A storm that impacted our region last Sunday/Monday dropped varying amounts of snow throughout our forecast zone. Placer Valley was the winner with 2-3’, Turnagain Pass had 8-14”, Girdwood Valley saw 7-10”, and Summit Lake with 4-6”. This new snow fell on weak old surfaces consisting of near surface facets and buried surface hoar. Over the last few days the new snow has been settling and adjusting as cold weather and light winds have kept this snow mostly loose and unconsolidated. Over the last few days there have been a handful of natural and skier triggered slides and few snowmachine triggered slabs. In Placer/Skookum Valley where the slab is thicker these avalanches have been on steep features proportionate to their terrain size. In Turnagain Pass where steeper slopes have seen heavier traffic, these slabs have been relatively small, and not quite large enough to bury a person. Determining whether the new snow will act as a slab is the current question and will determine what type of avalanche could be triggered. Furthermore, the deeper the new snow the larger the avalanche will be if a slab is triggered – such as in the Placer Valley. Questions to keep in mind today:  

  1. Is the snow loose and unconsolidated or is it becoming ‘slabby’ with daytime warming on Southerly facing slopes? A slope around noon could be stable only to heat up at 3pm and become unstable, taking out your prior tracks. 
  2. Was the snow affected by the winds during the storm and is it stiffer? Any slope where the new snow is acting like a slab will be suspect for triggering an avalanche. Expect poor bonding to the older/weaker snow below on all aspects. 
  3. What are the consequences of the terrain if I trigger an avalanche? Larger slopes have more potential to propagate a larger avalanche – especially in Placer/Skookum zone where the slab is thicker. Be aware of terrain traps such as gullies, cliffs or trees below you.

This is a possible natural or remote triggered slab on a Southwest aspect near the toe of the Skookum Glacier. Notice the three sledders on lookers left side of the photo for scale. This is a good example of a terrain trap that could catch you by suprise and also shows you the potential of a slab to propagate on a bigger slope. Photo taken on 3/21/17 by Lloyd Tesch.


A handful of natural and skier triggered avalanches on Magnum’s South face. Photo taken on 3/21/17 by Peter Wadsworth. 


Avalanche Problem 2
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Triggering loose fast moving ‘sluffs’ will be possible today in steep terrain and could knock you over and be larger than expected. On southerly aspects where a thin sun crust has formed triggering a sluff will be limited.  

Skier triggered sluff on the West face of Magnum from 3/21/17. 

Additional Concern
  • 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

As always, give cornices a wide berth and minimize exposure under them. 

GLIDE AVALANCHES?  Limit time under glide cracks. There is one on Seattle Ridge, left of the up-track, and some in the Skookum Valley along with others scattered about.


Thu, March 23rd, 2017

Yesterday skies were sunny and clear. Temperatures ranged from single digits F into the upper 20F’s below 2000′. In the alpine temperatures remained in the teens F with less fluctuation. Ridge top winds 5-10mph were from the West.  

Today looks very similar.   Daily temperatures may range from 0F into the mid 20F’s during the heat of the day. Valley fog is expected to burn off in the afternoon. Ridge top winds are expected to be in the 5-15mph range and no precipitation is expected.  

This stable and dry pattern is expected through Saturday. The first hint of precip in the forecast will be on Sunday as a Low in the Bering moves towards the Aleutians.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 14   0   0   65  
Summit Lake (1400′) 12   0   0   30  
Alyeska Mid (1700′)  19 0   0   59  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 12   WSW   6   12  
Seattle Ridge (2400′) 15   variable   2   8  
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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.