New snow drifted by wind may form reactive slabs at upper elevations. Anticipate changing conditions and monitor the depth, cohesiveness, and bond of the new snow to the old snow surface. A deep weak layer remains a concern.
Up to 10 cm of new snow may accumulate by Monday afternoon in favored areas. Wind slab avalanches may increase in their sensitivity to human-triggering where moderate southwest winds are loading the new snow into slabs on lee features.
Weak faceted snow near the base of the snowpack continues to be a concern. Treat wind-scoured, rocky, shallow terrain as suspect and avoid big alpine slopes that are threatened by cornices overhead.
Sunday night: Mostly cloudy, up to 5 cm of snow, light southwest wind with moderate gusts at ridge-tops, alpine temperature -7 C, freezing level 1000 m.
Monday: Mostly cloudy, scattered flurries with up to 5 cm of snow, light southwest wind, alpine temperature -6 C, freezing level 1500 m.
Tuesday: Mostly cloudy, 5-10 cm of snow, light southwest wind, alpine temperature -8 C, freezing level 1300 m.
Wednesday: Mix of sun and cloud, light west wind, alpine temperature -11 C, freezing level 1200 m.
Over the past several days, avalanche activity was reported as natural loose wet avalanches (size 1-2.5) running in steep, sun-exposed terrain. One large (size 2.5) cornice failed as a result of explosive mitigation.
Last week, there was a report of a skier remotely triggering (from a distance) a large (size 2) deep persistent slab avalanche at 2600 m on a northwest aspect. The avalanche was triggered from a thin spot, released 40-80 cm deep, and ran on depth hoar near the base of the snowpack.
If you decide to travel in the backcountry, consider sharing your observations via the Mountain Information Network (MIN) to supplement our data stream as operators are shutting down. A conservative mindset and margins are recommended at this time.
Up to 10 cm of new snow is forecast to accumulate by Monday afternoon in favored areas. Moderate southwest winds at ridge-tops may build wind slabs primed for human triggering on lee features.
The new snow is falling on a variety of snow surfaces, consisting of sun crusts, hard wind-affected snow, and soft faceted snow. There have also been reports of surface hoar forming on sheltered, shady slopes. See this MIN for a helpful illustration from nearby Glacier National Park. It will be important to track the depth, cohesiveness, and bond of the new snow to these various old snow surfaces across aspects and elevations where you are travelling.
Cornices are large and looming. Surface hoar buried February 22 may be found 50-100 cm deep. Avalanche activity on this layer was last reported March 11th.
Deeply buried facets lurk near the bottom of the snowpack. This layer has been responsible for sporadic deep persistent slab avalanches, usually triggered from shallow, rocky start zones.
