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Avalanche Forecast

Archived

Dec 19th, 2018–Dec 20th, 2018

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

Regions

Kootenay Boundary.

Expect snowfall and strong winds on Thursday, which will load a touchy weak layer buried 50 to 100 cm deep. Treat the danger as HIGH if you find more than 20 cm accumulation. It is a good day to stick to low-angled slopes without overhead exposure.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

WEDNESDAY NIGHT: Partly cloudy. THURSDAY: Cloudy with snowfall, accumulation 10 to 15 cm, strong southwest winds, alpine temperature -1°c, freezing level rising to 1600m over the day. FRIDAY: Partly cloudy, moderate west winds, alpine temperature -8°c, freezing level 1000m. SATURDAY: Partly cloudy, moderate southwest winds, alpine temperature -9 °c, freezing level valley bottom.

Avalanche Summary

Large (size 2 to 3) slab avalanches were triggered naturally, by skiers, and explosives on Tuesday and Wednesday. The avalanches were generally 50 to 70 cm deep and either within the storm snow or on the weak layer described in the snowpack discussion.

Snowpack Summary

Around 50 to 100 cm of recent storm snow overlies a weak layer of feathery surface hoar, sugary facets, and variable crusts. Avalanche activity, remote triggering, and snowpack test results tell us that it is a critical layer. It is best to travel extremely cautiously with this layer in the snowpack.Lower in the snowpack, previous weak layers from November appear inactive. These deeper layers could possibly cause problems on north-facing slopes at high elevations where the snowpack is thin.

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.

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.