Avalanche Forecast
Regions: Northwest Inland.
Wind-loaded pockets of recent storm snow will likely remain reactive to human triggering especially where it sits over surface hoar or sun crust.
Confidence
High -
Weather Forecast
Saturday night: A trace of new snow. Light to moderate west wind, increasing in the afternoon. Alpine low -11 C. Freezing level valley bottom.
Sunday: 5-10 cm new snow. Southeast wind easing to light. Alpine high -8 C. Freezing level 500 m.
Monday: Mix of sun and cloud. Light to moderate west wind. Alpine high -7 C. Freezing level 300 m.
Tuesday: Flurries. Moderate to strong west wind. Alpine high -4 C. Freezing level 300 m.
Avalanche Summary
A few natural wind slab avalanches up to size 1.5 were observed on north to east aspects on Friday.
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. Last 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. Last 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
10-15 cm of recent snow has been redistributed by strong westerly winds in exposed alpine and treeline areas. In sheltered areas, the new snow rests on a layer of surface hoar, and on a sun crust on solar aspects.
An older, patchy layer of small surface hoar crystals and 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 buried 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
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
- Approach steep, open and/or sparsely treed slopes cautiously.
- Storm slabs in motion may step down to deeply buried weak layers resulting in very large avalanches.
Avalanche Problems
Storm Slabs
10-15 cm of new snow and strong southwesterly winds have formed fresh storm slabs. 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: 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: Unlikely - Possible
Expected Size: 2.5 - 3.5