Turnagain Pass

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. 

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. 

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.