Avalanche Forecast

Issued: Feb 21st, 2020 4:00PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs and Deep Persistent Slabs.

Avalanche Canada JSmith, Avalanche Canada

Email

The new snow may be more reactive than expected to human triggers; especially on slopes where it has been wind loaded and is sitting on a layer of surface hoar.

Summary

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

FRIDAY NIGHT: 2-5 cm. snow, strong west wind, alpine temperature -7 C.

SATURDAY: 2-5 cm snow, moderate west wind, alpine temperature -3 C.

SUNDAY: Mostly cloudy, light southeast wind, alpine temperature -5 C.

MONDAY: Mix of sun and cloud, light west wind, alpine temperature -7 C.

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. 

Snowpack Summary

10 cm. of new snow and strong southwesterly winds have redistributed 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.

Problems

Storm Slabs

An icon showing Storm Slabs

10 cm of new snow and strong southwesterly winds have formed fresh storm slabs that will be reactive to human triggers. 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

An icon showing 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

Valid until: Feb 22nd, 2020 5:00PM