Turnagain Pass

Strong Easterly winds have been changing the surface conditions of our forecast zone over the last 4 days creating hard wind slabs on leeward features. Many ridgelines have been exposed down to rocks, dirt and old crusts. Observations yesterday found hard supportable wind slabs as low as 1600’ on Eddies. These slabs averaged around 5” thick and were failing in hand pits on old weak snow. Any wind slabs today will be hard and supportable (to a skiers weight) and may lure a skier well onto a slope before it fails. Be suspect of unsupported slopes steeper than 30 degrees that have a fat, smooth, pillow-type shape to them. Listen for that hollow, drum-like sound below your skis or use a pole to probe for that hard snow over weak set up.  These slabs could be as thick as 1-2’ deep in upper elevations and have the potential for initiating a much larger and more dangerous deep slab avalanche. More on this below. 

A handpit that failed on isolation on weak snow below, near surface facets and buried surface hoar. Yesterday at Eddies at 1900′ on a West aspect. 

Many windward slopes have eroded down to rocks, dirt, and crusts, but cross loading is still possible around gullies and terrain features on windward slopes. Photo of the SE face of Seattle Rigdge near Pyramid Peak. 

The recipe for deep slab avalanches has been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche during the early December storm cycle. The snowpack ranges from 3-5+’ thick and is sitting on weak basal facets. Observations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations. This is a high consequence avalanche problem that is impossible to outsmart.

When dealing with a deep slab avalanche problem, keep in mind:

• Large snow covered slopes that do not have piles of old debris under them are all suspect 
• Thinner areas of the snowpack (1-2’ thick) are likely trigger spots as well as scoured areas near rocks   
• It is possible to trigger this avalanche from below and it could run further than expected 
• Due to strong winds over the last month the snow depths are highly variable and there may be more trigger spots than we realize
• Thicker areas (3-5+’ thick) will be difficult to trigger and several tracks may be on a slope before someone finds a trigger point

This Deep Slab avalanche on the NW face of Pastoral was remotely triggered from below on Dec.20 by a party of two skiers who were able to run out of the way of the debris. This is an example of the potential that still lingers in upper elevations, above 3000′ on slopes that haven’t avalanched. For more details on the snowpack structure click HERE and for a description of what happened click HERE.