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Avalanche Forecast

Archived

Feb 10th, 2021–Feb 11th, 2021

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

Regions

Kootenay Boundary.

Although cold may cause our persistent slab problem to trend a bit less reactive, it also slows the process that would allow it to heal it into the snowpack. Instead of gambling on which effect is more significant, choose terrain that minimizes your exposure to the problem.

Confidence

Moderate -

Weather Forecast

Wednesday night: Clear. Light north winds.

Thursday: Sunny. Light northeast winds. Alpine high temperatures around -23.

Friday: Sunny. Light northeast winds. Alpine high temperatures around -20.

Saturday: Becoming cloudy. Light to moderate east winds. Alpine high temperatures around -18.

Avalanche Summary

We are still receiving reports of persistent slab avalanches, triggered by skiers and explosives, generally large (size 2-3) with wide propagation, at elevations around treeline (1800-2000 m) where our active persistent weak layer exists as surface hoar. Check out this great MIN describing a remotely triggered persistent slab avalanche in Kootenay Pass on Sunday. Most other MINs from the region from the past few days detail other persistent slab releases. 

An explosives-triggered persistent slab in the Bonningtons on Tuesday stepped down to our early December crust layer to produce a 200 cm-deep, size 3.5 (very large!) avalanche. A similar avalanche (size 3.5, step down to December crust) occurred naturally in the same area in the first week of February.

A natural storm slab cycle up to size 2 was observed Saturday. Explosive and skier controlled storm slabs to size 1.5 were produced through the weekend.

Snowpack Summary

Snow from the past week has seen some wind effect at upper elevations and may contain a freezing rain crust or surface hoar at lower elevations. It continues to settle over a reactive weak layer buried 60-80 cm deep. 

This persistent weak layer may exist as facets or a crust but it has been most reactive where it exists as large surface hoar crystals in sheltered areas treeline and below. Surface hoar has potential to surprise backcountry users with how widely the fracture can travel across slopes. This layer is slow to gain strength and requires careful terrain selection, even as its likelihood of triggering gradually diminishes.

There are potentially several more layers of surface hoar in the mid snowpack, with the most notable one down about 80-120 cm. This layer was buried in early January.

A crust surrounded by weak faceted grains is buried deep within the snowpack. It may be possible to trigger this layer with a large load in a shallow rocky start zone.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.