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Avalanche Forecast

Archived

Feb 16th, 2020–Feb 17th, 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.

Avoid steep, rocky, and wind affected areas where triggering slabs is more likely. Be ready to step back from sun exposed slopes in the afternoon.

Confidence

Moderate -

Weather Forecast

Sunday night: Clear. Light northwest winds. Alpine low -14 C. Freezing level valley bottom.

Monday: Mix of sun and cloud. Light northwest winds. Freezing level 700 m.

Tuesday: Mix of sun and cloud. Light northwest winds. Freezing level 700 m.

Wednesday: Sunny. Light northwest winds. Freezing level 700 m.

Avalanche Summary

Explosive and skier control work on Sunday produced size 1.5-2 storm slabs, and size 1 loose dry. Solar triggered loose dry avalanches to size 1.5 were also observed in steep south facing terrain.

Reports have been trickling in of deep persistent avalanches on deep weaknesses near the bottom of the snowpack. A 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 avalanches, 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 fully be ruled out even when surface instabilities are limited.

Snowpack Summary

Up to 40 cm of recent storm snow sits over 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 between 20 and 70 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

  • The best and safest riding will be on slopes that have soft snow without any slab properties.
  • Avoid freshly wind loaded terrain features.
  • Caution around slopes that are exposed to cornices overhead.
  • 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.