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Avalanche Forecast

Archived

Feb 13th, 2020–Feb 14th, 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.

Small but touchy new wind slabs are likely to form on the surface with forecast weather. Keep the big picture in mind as you manage new surface instabilities. Our snowpack has the capacity to produce very large avalanches with the right trigger in shallow rocky start zone.

Confidence

High -

Weather Forecast

Thursday night: Cloudy with flurries bringing 5-10 cm of new snow. Moderate to strong southwest winds, easing from an afternoon peak.

Friday: Cloudy with continuing isolated flurries and up to 5 cm of new snow. Moderate west winds, increasing a bit overnight. Alpine high temperatures around -8.

Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate southwest winds. Alpine high temperatures around -8.

Sunday: Cloudy with continuing scattered flurries and up to 5 cm of new snow. Light west or northwest winds. Alpine high temperatures around -8.

Avalanche Summary

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. No new avalanches were reported on Tuesday, however another recent large deep persistent slab is described in the following MIN report.

Over the weekend numerous natural, human triggered and control work induced avalanches to size 2 were observed, there is a great MIN that serves as an example of this kind of activity here.

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. The group was using excellent travel protocol and thankfully no one was hurt. 10 or so climbs had been made in the same area in the days leading up to this avalanche without incident - a great illustration of the tricky, low probability/high consequence nature of persistent slabs.  

Before the above avalanche, the last avalanche cycle to include persistent slabs was during the first weekend in February when some large (size 2.5) deep persistent slab avalanches in the Elk Valley (see photos in this MIN report) ran. 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

5 to 15 cm snow from last weekend's storm added to variable amounts of wind affected snow that sits above a widespread rain crust that exists up to roughly 2100 m. The storm snow has been formed into slabs by wind from a variety of directions. 

The Elk Valley has about 5-20 cm of snow above the crust while the eastern slope of the region has closer to 15-35 cm above the crust. There have been observations of surface hoar forming in the Elk Valley prior to Friday Night's storm, check that out here. 

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

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

Problems

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.

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.