It is possible to initiate a 60-70cm slab avalanche on the persistent weak layer. Snow deposited during Tuesday’s storm have coalesced in some places into a soft slab. This, combined with the buried persistent weak layer, warrant caution today.
Facets above and below the remains of the Lucky Friday Crust (1/13), buried 60-70cm from surface, have the potential to propagate. An avalanche on this layer is a low likelihood, high consequence scenario, most likely to be initiated where the snowpack is shallow around trigger points on steep slopes, or when a smaller avalanche steps down.
Tuesday’s snow has coalesced into a widely distributed soft slab where it was sheltered from strong winds. Slabs will be thicker and harder where strong south and southwest winds accompanying Tuesday’s storm, transported snow to below ridge lines and onto cross loaded terrain. Be alert to density changes and snow surfaces that crack underfoot. There is the danger of a storm/wind slab avalanche stepping down into the deeper buried persistent weak layer, initiating a larger slide.
Yesterday Kyla and I toured up West Willow Peak toward Stevens. With the ambient air temp hovering right around freezing and a bluebird sky, it was a great day to be out and about. The cold clear conditions Wednesday night drove the formation of well-developed surface hoar that sparkled in the sunlight. Also, there was a healthy dose of grapple mixed in with Tuesday’s storm snow. Hopefully the surface hoar and grapple will be broken down by wind and sun over the next few days before its buried in the next storm.
Tuesday’s storm blanketed the mountains in a fresh layer of soft snow. We found enough cohesion in the new snow layer to propagate a 9inch soft slab in sheltered trees at 6300ft on a southwest aspect. The storm rolled in with abundant wind from the south and southwest that transported snow onto the lee side of ridges and cross loaded gullies. Look for wind loading on north and east aspects. Wind slabs gain strength with each passing day after they have formed, but yesterday we were still seeing failure potential in the upper 12inches of the snowpack at various storm/wind slab interfaces on multiple aspects and elevations. There is the danger that a slide initiated in one of these layers could step down into a more deeply buried persistent layer.
Although it has taken on different forms on different aspects and elevations, the Lucky Friday Crust and the facets both above and below are showing reactivity with hard blows in pit tests. At mid elevation the crust appears as a 10cm rotten cavity about 60cm from surface. At or above tree line it appears as thin weak crust. Both configurations showed the potential to propagate, meaning an avalanche on this layer, while not likely, is possible. I have greater concern about snowmobiles, with their increased weight and depth of penetration, initiating this layer than skiers or snowboarders.
The upper snowpack remains soft and light. Although it might be tempting to drop some bigger lines, I would be cautious stepping out today. I suggest digging hasty pits to below the Lucky Friday Crust layer on slopes you are considering riding to get an idea of the reactivity of various storm layers and buried weak layers. Fun riding conditions abound on all aspects. A mellow sloped ride through the trees might be the right call today.
If you get out into the mountains this week, please consider posting an observation. Forecasters are only able to cover a finite area each week on our field days. Observations help us better understand what avalanche problems are present across the forecast zone.
There are a few spots still open in FIPAC’s upcoming Avy 1 courses. If you have not completed an Avy 1 class, or it has been a long time, please consider attending. Click the education tab, above right, for more details.
