Avalanche Forecast

Archived

Mar 5th, 2021–Mar 6th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Kootenay Boundary.

Incremental snowfall and moderate winds from the southwest may form fresh wind slabs at upper elevations that could be possible to trigger. Monitor for these conditions where you travel.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Friday night: Mostly cloudy, isolated flurries with trace accumulations moderate southwest wind, freezing level dropping to 1100 m.

Saturday: Mostly cloudy, 5-10 cm of snow, moderate southwest wind, freezing level rising to 1500 m and dropping to 500 m overnight.

Sunday: Mostly cloudy, 5-10 cm of snow, moderate southwest wind, freezing level rising to 1300 m and dropping to valley bottom overnight.

Monday: Partly cloudy, light southwest wind, freezing level rising to 1200 m.

Avalanche Summary

Numerous small to large (size 1-2) wet loose avalanches released naturally on south-facing aspects up to 2000 m during the past few days of sunny, warm weather.

Last weekend, large explosives produced very large (size 2-3) results at Kootenay Pass. In thin snowpack areas on solar aspects, a few of these large avalanches are suspected to have stepped down to the January layer described in the snowpack summary.

Snowpack Summary

A gradual cooling trend will improve the overall snowpack stability. 5-10 cm of new snow is forecast to accumulate by midday Saturday. Shallow wind slabs may form as a result of moderate southwest winds at ridgetop on lee features.

At upper elevations, snow is wind-pressed in most exposed areas, and a melt freeze crust has formed on sunny slopes. In shaded, sheltered areas, 15-30 cm of well-settled snow may sit over a layer of small surface hoar crystals buried Feb 25th. A more prominent persistent weak layer from late January is buried 80-150 cm deep and is composed of a combination of surface hoar, crusts, and facets. The past few days of warm weather were likely the final test on these layers. There is some lingering uncertainty about whether this problem remains reactive on isolated upper elevation slopes on solar aspects in thin snowpack areas.

As described in this MIN report, shallow snowpack areas in the east of the region may harbor a faceted basal snowpack. This structure can typically be managed by avoiding shallow rocky areas where the snowpack transitions from thick to thin.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.