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Avalanche Forecast

Archived

Feb 25th, 2020–Feb 26th, 2020

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

Regions

Kootenay Boundary.

Human triggering of storm slabs remains possible. Caution around wind loaded features and convexities in the alpine and upper treeline.

Confidence

High - The number, quality, or consistency of field observations is good, and supports our confidence.

Weather Forecast

Tuesday night: A trace of new snow. Moderate west wind. Freezing level 1000 m.

Wednesday: Cloudy. Moderate northwest wind. Freezing level 1500 m.

Thursday: Mix of sun and cloud. Moderate southwest wind. Freezing level 1700 m.

Friday: Mix of sun and cloud. Moderate southwest wind. Freezing level 2100 m.

Avalanche Summary

A skier triggered wind slab avalanche size 2 was reported on a wind loaded northeast aspect near ridgetop. A few small loose wet avalanches ran on steep solar features during clear periods Tuesday.

On Monday, numerous natural, explosive, skier triggered, and remotely triggered storm slab avalanches were observed size 1-2 on all aspects at alpine and upper treeline elevations. 

A natural avalanche cycle occurred Sunday, consisting of size 1-1.5 loose dry and soft slab avalanches. Activity was observed on various aspects but was especially concentrated on southeast to southwest where they ran on the surface hoar/crust combo. 

Snowpack Summary

15-30 cm of recent snow is settling over a layer of surface facets, surface hoar in sheltered shady aspects or sun crusts on solar aspects. In the alpine and exposed treeline, recent snow has been redistributed by strong southwest to northwest wind, loading deep deposits into lee features.

An older layer of surface hoar now sits 30-50 cm deep. This weak layer produced significant avalanche activity focused in the east of the region prior to the last storm. While it is likely bonding over time, there is uncertainty around remnant reactivity. The remainder of the snowpack is well settled.

Terrain and Travel

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.

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.