Analyze the snow surface for patterns of wind redistribution to navigate around wind slab problems at higher elevations.
Light new snow amounts and elevated southwest winds have formed reactive new wind slabs over leeward (north to east) terrain. The most suspect terrain is immediately adjacent to ridges at treeline and alpine elevations. Note that cornices are large, looming, and could fail under the weight of a person or machine.
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In the north of the region (e.g. Duffey, Hurley, Goldbridge), a deeper persistent weak layer of faceted grains near the ground presents a lingering concern on steep, shallow slopes in the alpine.
Wednesday night: Clear periods. Light to moderate northwest winds.
Thursday: A mix of sun and cloud with cloud increasing in the afternoon. Light northwest winds. Alpine high temperatures around -12.
Friday: Cloudy with isolated flurries and up to 5 cm of new snow. Moderate northeast winds. Alpine temperatures dropping to around -16.
Saturday: A mix of sun and cloud. Light to moderate northeast winds. Alpine high temperatures around -18.
Up to 15 cm of new snow and strong winds were observed forming reactive wind slabs throughout the region on Tuesday.These recent wind slab formations may remain reactive to human triggering on Friday.
Pemberton SAR responded to a cornice collapse involvement in the Duffey Lake area on Monday when a large chunk of cornice released and collided with a rider in steep terrain on a lower elevation (1700m) feature. The impact of the cornice failed to trigger a slab but it did entrain loose snow that contributed to the full burial of the subject.
On Sunday there was a skier triggered size 2 persistent slab avalanche in the north of the region that is suspected to have run on weak facets that were buried in late November. It was on a northwest aspect at 2200 m and may have been a slope that had slid previously and was reloaded.
On Friday, explosives triggered cornices and 20 cm slabs within the recent storm snow, producing small (size 1 to 1.5) up to large (size 2) avalanches. The avalanches were on west to north aspects and at alpine elevations. A persistent slab avalanche was triggered by a rider in the northern part of the region, likely releasing on the February 22 surface hoar layer described in our Snowpack Summary. The avalanche was large (size 2) and occurred on a north aspect in the alpine.
5 to 15 cm of new snow accumulated in the region during Tuesday's storm, accompanied by moderate to strong south and west winds. As a result, new wind slabs up to 30 cm deep have been observed on leeward slopes. The new snow also buried surface hoar in more sheltered areas as well as sun crusts on south-facing slopes.
Another weak layer of surface hoar crystals and/or faceted grains may currently be found around 50 to 80 cm deep on northerly aspects at treeline and lower alpine elevations. This distribution of this layer is spotty, likely existing as a problem only in isolated steep, sheltered, north-facing slopes at mid elevations. Professionals throughout the region have begun to consider it dormant.
In the northern part of the region (i.e., Duffey/Hurley/Gold Bridge), a deep instability may linger at the base of the snowpack. It has not produced an avalanche since February 17th. Human-triggering is unlikely, though if one were to trigger the layer, it would likely be in a thin, shallow, rocky spot. A large load, such as from a cornice fall, or sustained warm temperatures have the potential to trigger this layer.
