Turnagain Pass

Today elevated Southeast winds, 10-30mph, may be moving snow around in the alpine depending on where you travel. As of early this morning Seattle Ridge has been recording wind speeds in the 10-20mph range while Sunburst had remained protected. Loose surface snow is available for transport and it will be important to monitor surface conditions and watch for blowing snow as you travel. Small pockets of newly formed wind slabs may be tender on leeward features, but more concerning will be drifting snow adding stress to a persistent slab.  Several weak layers are buried within the top 1-2’ of the snowpack, including buried surface hoar and near surface facets. Avoid smooth pillowed surfaces in steep terrain or slopes with active wind loading. Shooting cracks or ‘whumpfing’ sounds will be obvious clues that the snow is unstable.    

*Deep Persistent Slab:  Weak snow can still be found near the ground in the upper elevations of our forecast area, 3,000′ – 5,000′. Although triggering a Deep Persistent Slab is unlikely, it is worth keeping in mind that poor structure does exist in places with a generally thinner snowpack. The Southern end of Turnagain Pass and Summit Lake zone are more suspect, and it wouldn’t be impossible to trigger in another part of our forecast zone with shallow snow cover. On Saturday (Feb.3) a large human triggered avalanche occurred on the East face of Twin Peaks and failed on weak snow (buried surface hoar and facets) sitting on a hard bed surface. Although the size of this avalanche is shy of 1 meter deep (a deep slab criteria,) its behavior is pretty much the same. This was a high consequence, hard to trigger avalanche where the 9th and10th skiers on a skin track found just the right trigger spot in a very shallow part of the snowpack. Luckily no one was caught or injured in this avalanche. A conservative approach would be to avoid large steep terrain with a shallow snowpack and exposed rocks. 

Earlier in the week wind affected snow was observed on the Northern end of Turnagain Pass on Eddies to Wolverine. This is a good example of where a shallow wind slab or a persistent slab may be lurking.  

 An avalanche triggered on the skin track at 3400′ on the East face of Twin Peaks on Saturday, Feb. 3, 2018.   

Crown profile about 30′ away from the trigger spot shows several weak layers including older weak snow near the ground where this avalanche failed, and recently buried surface hoar in upper layers. 

Cornices: In windy areas cornices may be seeing additional stress today. Cornices are unpredictable and can break further back along a ridge than expected. Give these features plenty of space and avoid traveling underneath them. 

Loose snow avalanches ’sluffs’: In places protected from winds, expect loose surface snow to be small in volume, but could slide easily in steeper terrain with the weight of a person. Watch your ‘sluff’ and be aware of the consequences below you.