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Avalanche Forecast

Archived

Feb 24th, 2020–Feb 25th, 2020

Alpine
Natural avalanches possible, human triggered probable.
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.
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.

Storm slabs are sitting over a weak layer and continue to be reactive. Some uncertainty surrounds a deeper weakness which, if triggered, could produce high consequence avalanches. Uncertainty is best managed by conservative terrain choices and avoiding terrain traps.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Monday night: Clear. Light to moderate northwest wind. Freezing level valley bottom.

Tuesday: Mix of sun and cloud. Light to moderate northwest wind. Freezing level 1200 m.

Wednesday: Mix of sun and cloud. Moderate northwest wind. Freezing level 1500 m.

Thursday: Mix of sun and cloud. Light to moderate northwest wind. Freezing level 1800 m.

Avalanche Summary

A natural avalanche cycle occurred Sunday afternoon and overnight, 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. Slabs were reported to be touchy and easily triggered by skier traffic. Explosive control work conducted Monday produced size 1.5-2 running far on the crust. Reactivity is expected to continue.

Snowpack Summary

15-30 cm of recent snow is settling into a storm slab over a layer of widespread surface facets, surface hoar in sheltered areas 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 last week. While it is likely bonding over time, there is uncertainty around remnant reactivity. The remainder of the snowpack is well settled.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
  • Be aware of the potential for human triggerable storm slabs at lower elevations, even on small features.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

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.