Turnagain Pass

Be suspect of unsupported slopes steeper than 30 degrees that have a fat, smooth, pillow-type shape to them. Strong Easterly winds over the weekend changed the surface conditions of our forecast zone, creating hard wind slabs on leeward features. The wind slabs may be farther down slope due to the high wind speeds or only found on one side of gully features due to cross loading. Observations Sunday 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), they could be stubborn to initiate and may lure a skier well onto a slope before it fails. 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 if triggered in the alpine have the potential to initiate a much larger and more dangerous deep slab avalanche. More on this below in the secondary concern. 

Cross loading on Seattle Ridge.

Deep slab avalanches have been a concern in the advisory now for two weeks. We are not trying sound like a broken record but the message is the same. This set-up continues to warrant elevated caution and respect. This is a high consequence avalanche problem that is impossible to outsmart. The snowpack 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.  

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. Choose terrain wisely!
• 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

Obvious clues like ‘whumpfing’ and shooting cracks may not be present until it is too late. Evaluate snow and terrain very carefully and steer clear of large loaded slopes. 

Poor snowpack structure in the alpine, hard snow over weak snow near the ground. 

 Pastoral. Remotely triggered Deep Slab avalanche that occured on December 20th, 2017.