Avalanche Forecast
Regions: Northwest Inland.
Storm slabs will build through the day Friday with up to 20 cm of new snow falling amid strong winds. Storm slabs will be especially reactive where freshly wind loaded pockets sit over surface hoar or sun crusts.
Confidence
Moderate -
Weather Forecast
Thursday night: 5-10 cm new snow. Southwest wind increasing to extreme. Freezing level 800 m.
Friday: 5-10 cm new snow. Strong southwest wind. Freezing level 1000 m.
Saturday: Mix of sun and cloud with isolated flurries. Moderate southwest wind. Freezing level 600 m.
Sunday: Cloudy with isolated flurries. Moderate southeast wind. Freezing level 400 m.Â
Avalanche Summary
Some very large and destructive avalanches have been sporadically running on deeply buried weak layers near the bottom of the snowpack, predominantly on north through east aspects in the alpine. On Tuesday, a natural size 2.5 was observed. It is suspected to have started as a wind slab in a thin rocky area before stepping down. On Monday, two deep persistent slab avalanches size 2-3 were triggered from thin snowpack areas by very large loads pushed by snowcats.Â
Snowpack Summary
10-20 cm of new snow is forecast to fall by the end of the day Friday. Strong winds are redistributing the new snow in exposed alpine and treeline areas, over extensively wind affected old surfaces. In sheltered areas, the new snow falls on a layer of surface hoar, and onto a sun crust on solar aspects.
An older, patchy layer of small surface hoar crystals a sun crust both from early February may still exist under previous storm snow, 30-60 cm deep.
A couple of weak layers that formed in January are burried in close proximity to one another 80-140 cm below the surface and continue to give hard results in snowpack tests. Below, an early season crust lurks at the base of the snowpack. Some large avalanches have been triggered on these layers, usually during periods of rapid loading by new snow or wind and by large loads or from thin, rocky areas.
Terrain and Travel
- Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
- Approach steep, open and/or sparsely treed slopes cautiously.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Storm slabs in motion may step down to deeply buried weak layers resulting in very large avalanches.
Avalanche Problems
Storm Slabs
10-20 cm of new snow is forecast to fall by the end of the day Friday. Strong winds are expected to redistribute new snow into deeper slabs in lee features. Storm slabs will be especially reactive where freshly wind loaded pockets sit over surface hoar or sun crusts.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 1.5
Deep Persistent Slabs
Some very large and destructive avalanches have been sporadically failing on deeply buried weak layers, predominantly on north through east aspects in the alpine. The bulk of events occur during periods of rapid loading by new snow or wind, or are triggered by very large loads (wind slab avalanche, cornice or snowcat).
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 2.5 - 3.5