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Avalanche Forecast

Archived

Mar 11th, 2020–Mar 12th, 2020

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

The snowpack in our region has become complex, with multiple avalanche problems and weak layers in play. Picking out which layer or layers you're managing on a given slope carries lots of uncertainty, so manage it with conservative terrain selection.

Confidence

High -

Weather Forecast

Wednesday night: Clear periods. Light to moderate northwest winds.

Thursday: A mix of sun and cloud. Light northwest winds. Alpine high temperatures around -10.

Friday: Cloudy with flurries bringing about 5 cm of new snow, easing overnight. Moderate east winds increasing over the day. Alpine temperatures dropping to about -15.

Saturday: Mainly cloudy with isolated flurries and a further trace of low density new snow. New snow totals of 10-20 cm. Alpine high temperatures around -19.

Avalanche Summary

Numerous small avalanches were triggered naturally and with skier traffic during the peak of Tuesday's storm, with crown depths between 5-30 cm deep suggesting both wind redistribution and the potential for multiple storm slab failure planes in the upper snowpack.

Two large (size 2 and 2.5) persistent slab avalanches were triggered by a skier and intentionally with a large snow machine on Monday. Both ran on the February surface hoar layer described in our Snowpack Summary and occurred on north and northeast aspects around treeline and below.

Over the past two weeks, small to large (size 1 to 2) avalanches have released on this surface hoar layer. They have most often released between 1800 and 2300 m on northwest to east aspects. This trend is suspected to continue as this layer slowly gains strength.

Snowpack Summary

10-20 cm of new snow accumulated in the region during Tuesday's storm. The new snow buried a thin new weak layer of surface hoar on shaded aspects as well as new sun crusts on more sun-exposed slopes. Numerous storm slabs were observed failing at this interface on Tuesday.

The new snow adds to 10-15 cm of snow in the west of the region and 20 to 35 cm in the east of the region from the past weekend. In some cases, the interface below this older storm snow may act as a secondary failure plane in the upper snowpack.

Collectively, these recent snowfalls have been loading a layer of feathery surface hoar crystals from late February that is now found 50 to 80 cm deep. This layer is most commonly found in open trees (e.g. in this MIN) or sheltered terrain around the upper part of below treeline, treeline, and lower alpine elevations. Check out the latest forecaster blog that offers a deeper dive into these conditions.

The remainder of the snowpack is strong and well-settled.

Terrain and Travel

  • Use careful route-finding and stick to moderate slope angles with low consequences.
  • Avoid freshly wind loaded terrain features.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.