Turnagain Pass

Today is a transition day. We have had mostly cold, clear weather this week. Snow is forecasted to start falling this morning and winds are increasing, gusting into the 30s. The new snow will be falling on very weak surface snow. There is widespread surface hoar, with near-surface facets below.  In the terrain around  2000′ and below, this weak snow is more developed and is sitting on the New Year’s melt-freeze crust. This has the potential to act as a bed surface. As the weather comes in today it will be important to pay attention to changing conditions. Slabs may form quickly, especially in leeward terrain. Quick hand pits or riding small terrain features can help check whether or not the new snow is sticking to the old snow surfaces. In steep terrain the weak surface snow can also act as a few inches of fast moving loose surface snow “sluff” that could catch you by surprise if you’re not expecting it. 

Surface hoar in the sunshine on Tuesday at 1700′ on Sunburst, photo: Ray Koleser.

As we anticipate the weak snow on the surface getting buried today don’t forget the old buried weak layers.  The chances of triggering a persistent slab avalanche have been decreasing. However, it is not something that should totally be ruled out yet. We know that the snow from the New Year’s storm snow is sitting on either buried surface hoar, buried near-surface facets or in thin snowpack areas, facets near the ground. This means there is poor snowpack structure and a persistent slab set-up above 2500′. Snowpack tests over the past few days have shown variable results but point to the continued potential for triggering an avalanche.

For those riders and skiers headed out today:

• Triggering a slab is most likely in the upper elevations above 2,500′, where NO crusts exist in the top foot of the snowpack.
• Several tracks may be on the slope before a slab releases and no signs saying ‘the slope is unstable’ are likely to be present.
• Larger slopes, 35 degrees and steeper are more suspect and those with rocky features. 
• Practice safe travel habits: expose only one person at a time, have an escape route planned, watch your buddies closely and view slopes as avalanche paths. If the snow does slide, where will it go? Avoid terrain traps. 

Watch Wendy’s Extended Column Test from yesterday, January 10th, on Seattle Ridge. It took some harder hits but still propagated (failed across the weak layer). This layer could still produce an avalanche.

Wendy’s pit yesterday was near her pit location on Sunday. She had very similar results. The slab yesterday was a little deeper. 

A poor snowpack structure still exists at high elevations above 3,000’, human triggered large and dangerous, deep slab persistent avalanches are still possible. Weak sugary snow (basal facets) near the ground is creating a low probability/high consequence avalanche problem. Likely trigger spots will be in thinner areas of the snowpack that are connected to large, loaded slopes. Signs of instability will not likely be present and there may be tracks on the slope. The possibility of a deep slab avalanche should still be part of your decision-making before committing to big terrain in the Alpine.