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RegisterMar 24th, 2018–Mar 25th, 2018
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The threat of Wind Slab avalanches is maintaining heightened avalanche conditions. You will be able to trigger a wind slab avalanche on steep wind-loaded slopes with convex rollovers, unsupported features, or below fresh cornices. You can stay safe by steering around these pieces of terrain where you see snow drifts, cornices, and firm snow that produces cracking.
Today you can trigger avalanches in the recently fallen snow. New snow and wind are maintaining elevated avalanche conditions. You can trigger Wind Slab avalanches on steep slopes near ridge tops or in cross-loaded areas including: convex rollovers, steep unsupported slopes (ending in rocks or cliffs), or below fresh cornices. Clues such as variable snow height, drifts, cornices, and stiff snow surfaces that produce cracking are signs that you should stay off of steep, unsupported slopes. Steering around these features is the best way to keep from triggering an avalanche today.
It has been more than two weeks since the last reported avalanche involving older weak layers. Some of these layers have not gone away, but they are now very difficult to trigger. With the current conditions, Persistent Slab avalanches will remain unlikely, though not impossible. This is a low likelihood high consequence scenario. Snowpack tests can provide useful information about buried weak layers, they are not a decision-making tool.
The strong March sun can quickly change conditions on slopes receiving direct sunshine. If the sun comes out, expect small loose wet avalanches, rollerballs, and pinwheels. Be ready to move off of and avoid steep sunny slopes during periods of intense sunshine.
Almost 2 feet of snow fell in the Cascade West South region since Wednesday. Winds during the storm transported snow forming wind slabs near ridgelines and on cross-loaded features. Observers reported avalanches within the recent snow and at the interface of the recent snow and old snow layers.
Rain on Thursday reach around 5500’ before transitioning to snow. This formed a new rain crust and created a generally good bond between the old and new snow. Below this rain line a wet and refreezing snowpack can be found. Above the rain line, the new snow fell on a variety of old snow surfaces. On sunny aspects, firm melt-freeze crusts have formed during the recent clear weather. In shaded locations, near surface facets and soft settled snow were observed earlier in the week. This may form a new buried weak layer within the snowpack.
An old weak layer of sugary facets (2/13) can still be found in some locations just above a very firm and wide spread crust (2/8). This pronounced crust has typically been found about 4-6 feet below the snow surface in the Crystal and Paradise areas You are most likely to find this layer still intact on shaded aspects near and above treeline.
Observations
South
On Saturday NWAC Forecaster Dallas Glass reported multiple natural and triggered Wind Slab avalanches on North, East, and Southwest aspects above 5,500 ft. The largest was almost 2 feet deep and involved all of the snow that fell since Wednesday. Dallas also reported sudden test results on the 2/13 facets over 6 feet below the snow surface.
On Wednesday NWAC professional observer Jeremy Allyn traveled in the Crystal backcountry. Jeremy found a firm and supportable surface crust on S-facing slopes. On shaded slopes, he reported soft snow. The 2/8 crust was down about 4 feet and still reactive in snowpack tests.