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Avalanche Forecast

Archived

Feb 14th, 2020–Feb 15th, 2020

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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Rockies.

New snow and wind has reactivated our wind slab problem at higher elevations. Seek out sheltered areas holding low density snow for the best and safest skiing and riding.

Confidence

High -

Weather Forecast

Friday night: Mainly cloudy with continuing isolated flurries and a trace of new snow. Moderate west winds, becoming strong at ridgetop.

Saturday: Cloudy with isolated flurries and a trace of new snow, increasing a bit overnight. Moderate southwest winds, strong at ridgetop. Alpine high temperatures around -8.

Sunday: A mix of sun and cloud with isolates flurries and up to 5 cm of new snow. Light west winds. Alpine high temperatures around -9.

Monday: Mainly sunny. Light west winds. Alpine high temperatures around -10.

Avalanche Summary

Locally enhanced snowfall in the Castle area over Thursday night led to a moderate rise in avalanche activity in that part of the region of Friday. Preliminary reports show ski cutting and explosives control yielding mainly small (size 1) dry loose releases. One natural size 1.5 storm slab was also observed, giving some indication of conditions in the range.

Over the last few days, reported avalanche activity was mainly limited to small dry loose avalanches and small wind slabs triggered with ski cutting and explosives control, however another recent large deep persistent slab is described in the following MIN report.

There was also a bigger avalanche reported in this MIN on February 9th (check out the photos, they're humbling). The very large avalanche ran on a north facing feature at 2400 m and was triggered by a snowmobile. 10 or so climbs had been made in the same area in the days leading up to this avalanche without incident.

Before the above avalanche, the last avalanche cycle to include persistent slabs was during the first weekend in February. These patterns of activity suggest our deep persistent slab problem may resurface more decisively during stormy periods but also that it can't easily be ruled out even when surface instabilities are limited.

Snowpack Summary

Another variable 5-20 cm of new snow accumulated in the region over Thursday night, with the Castle area appearing to hold the most substantial amounts.

The new snow buried mainly wind-affected surfaces and aging wind slabs in exposed areas, while adding to about 10-30 cm of older settled storm snow in sheltered areas. This brings snow totals above our widespread rain crust to about 20 to a possible 50 cm, with the east slope of the region again generally holding the deeper amounts.

We have previous observations of surface hoar forming in the Elk Valley in advance of last Friday's storm (see here), meaning this weak layer is now likely about 20 cm deep in that part of the region, and possibly elsewhere as well.

A well consolidated mid-pack overlies generally weak basal facets, that may be possible to trigger in isolated shallow rocky start zones.

Terrain and Travel

  • Caution around slopes that are exposed to cornices overhead.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.