Turnagain Pass Avalanche Forecast

It has been over a week since a large avalanche was triggered on Pastoral by two skiers traveling below the NW face. If you have been reading the forecast regularly we are not trying sound like a broken record but the message is the same. This snow pack set-up continues to warrant elevated caution and respect. It is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. The ingredients for a deep slab avalanche have been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche in the early December storm cycle. This is a hard slab, 3-5+ feet thick, sitting on top of weak sugary snow (basal facets) near the ground. 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 large piles of old debris under them are all suspect 
• Thinner areas of the snowpack (1-2 feet 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 
• Snow depths are highly variable and there may be more trigger spots than we realize
• Several tracks on a slope do not mean the conditions are safe. It could be the 2nd, 3rd or 10th person on a slope before someone finds a trigger spot.

Weak faceted snow near the ground continues to be reactive and signal propagation potential in test pits in the alpine. Check out a video HERE and observation from Magnum on 12/27/17 HERE. 

Over the last two weeks we have been trying to inventory terrain that has or has not avalanched like this observation sent yesterday from Seattle Creek. Photo taken and annotated by Peter Wadsworth. Check out his observation HERE.

Cold temperatures and stable weather this week have been making the snow more brittle and faceting out surfaces. With that said triggering an old wind slab is still possible on very steep terrain in the alpine zone. Places you might find a hard wind slab will be in steep couloirs, large unsupported terrain features, or in thin rocky areas. Triggering a wind slab in the Treeline zone is becoming less likely, but is not out of the question in high consequence terrain. This also goes for a few inches of fast moving loose surface snow “sluff” that could catch you by surprise if you’re not expecting it. Triggering a wind slab could take you for an undesirable ride, and has the potential for initiating a much larger and more dangerous avalanche above 3000′. Be suspect of any slopes that may harbor a deep slab problem in the upper elevations as described above. 

Thin wind slab crowns from a wind event that ended Dec.24 were seen on North and West aspects in Seattle Creek yesterday, as well loose surface snow. Photo by Peter Wadsworth.