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Avalanche Forecast

Archived

Dec 24th, 2021–Dec 25th, 2021

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 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.

Regions

Kootenay Boundary.

A suspicious layer of surface hoar is buried under the new snow, and responsible for recent avalanches - dig down and investigate the slab properties of the new snow and bond with the old surface.

Confidence

Moderate -

Weather Forecast

Light to heavy snowfall is expected across southern BC Friday night through Sunday. An easterly arctic front meeting a southwesterly flow will produce enhanced snowfall where this clash occurs; a band of heavy snowfall is forecasted to clip the Kootenay Pass area.

Friday Night: Flurries, 10-20 cm new snow overnight, Kootenay pass is expected to see the deepest deposits. Moderate and gusty southerly winds. Treeline temperatures near -10 and freezing level at valley bottom.

Saturday: Ongoing scattered flurries, 5-10 cm. Moderate gusty southerly winds. Treeline temperatures near -10 and freezing levels at the valley bottom.

Sunday: Cloudy and flurries, up to 7-12 cm. Light winds from the southwest and colder temperatures at -13.

Monday: Cloudy with sunny breaks. Light winds from the southwest and colder temperatures at -13.

Avalanche Summary

On Thursday, several natural and skier-controlled storm slab avalanches up to size 2 were reported, and explosives triggered slab avalanches to size 2.5; avalanches ranged from 20-60 cm deep.

Snowpack Summary

20-40 cm of recent storm snow overlies a thin freezing rain crust and a surface hoar interface. Recent westerly winds have pressed surfaces and loaded leeward features.

The upper snowpack overlies a substantial crust from early December. This crust is approximately 70-100 cm below the surface, 10 cm thick on average, and is present across all aspects to at least 2300m. A layer of weak facets (sugary snow) has been reported above this crust. 

The lower snowpack is composed of several early-season crusts. Snow depths at treeline average 150-200 cm. Below 1800 m the snowpack remains relatively shallow with 80-120 cm on average. The deepest snowpack can be found in the Kootenay Pass area.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Start with conservative lines and watch for clues of instability.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Dial back your terrain choices if you are seeing more than 25cm of new snow.

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.