Turnagain Pass

Triggering a fresh wind slab avalanche will be our main concern. Ridgetop winds from the Northwest picked up yesterday and have strengthened overnight. Several wind slabs (mostly small, some large) were reported in the Turnagain Pass area along with one large natural seen in the Skookum Valley. These were around 1 foot thick and running far – due to entrainment of 4-8+” of loose snow sitting on hard old surfaces. The increase in wind overnight will only increase the size and likelihood of triggering these slabs. Although winds are forecast to decrease today, they could persist through the daylight hours. Unusual loading patterns have been seen with this wind direction and therefore all aspects are suspect. Wind slabs should be mostly found in the Alpine above the trees, but could also be found in open areas in the trees. 

What to watch for:
–  Recent avalanches – take a look around today, visibility should be good
–  Shooting cracks from your snowmachine/skis/board
–  Areas that are currently being wind loaded or that ‘look’ as they have been recently – round and pillowed surfaces
–  Watch out from above – a party yesterday was washed over by a natural wind slab/sluff to their waist.

*Wind slabs are a surface instability that can typically be easily identified if we watch for them. Unlike the deeper weak layers mentioned below.

Sluffs: Sluffing in Friday’s storm snow (4-8+”) will be likely on steep slopes again today. 

Solar effects:  If the winds die down enough on South facing slopes, the sun will have a good chance at warming the surface creating moist sluffs and possibly triggering a fresh wind slab. In this case, avoid steep solar aspects if you notice roller balls or point releases under rocks. 

Natural and skier triggered sluffs and wind slabs seen in the Magnum/Cornbiscuit (Subperbowl and Goldpan) area yesterday. (Photo: Mike Records)

Sluff on the North side of Magnum – seen from Sunburst ridge. (Photo: Allen Dahl)

Cracking in the new snow – sign of finding a wind slab. (Photo: Allen Dahl)

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Triggering a slab avalanche breaking in persistent weak layers 1-3 feet deep remains possible above 1000’. Additionally, a wind slab or sluff has the potential to step down and trigger one of these layers. A layer of buried surface hoar from Jan. 21st continues to show signs of reactivity in the upper elevations, and a layer of facets over a melt-freeze crust is suspect in the mid elevation band. Be suspect of the older snow under Friday’s storm snow. Red flags like shooting cracks or “whumpfing” may not be present before a slope releases. Evaluate the terrain for consequences and be aware of places that haven’t seen much traffic. These less traveled places are more suspect for triggering these deeper layers.

Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could ‘wake up’ if the wrong spot is found above 3,000′. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass.