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Avalanche Forecast

Archived

Dec 12th, 2019–Dec 13th, 2019

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

Regions

Cariboos.

New snow sitting on a layer of surface hoar may be a recipe for thin but reactive storm slabs over the next few days.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Thursday Night: Flurries accumulating up to 5 cm. Alpine low -6, moderate southwest wind.

Friday: Flurries with trace accumulation, alpine temperature -4, light northwest wind.

Saturday: Mainly cloudy, isolated flurries with trace accumulation, alpine temperature -8, light northwest wind.

Sunday: Mainly cloudy, isolated flurries with trace accumulation, alpine temperature -10, moderate northwest wind.

Avalanche Summary

Reports from today included sloughing and loose dry size 1 avalanches in the storm snow, as well as a persistent slab avalanche triggered remotely by a helicopter. It is important to keep in mind the potential for large, persistent slab avalanches.

Snowpack Summary

A total depth of 150-250 cm of snow sits in the alpine in central parts of the region. 5-10 cm of new snow has covered a layer of feathery surface hoar crystals that were observed at all elevations throughout the region. We will be keeping an eye on this layer as it gets buried further.

The primary layers of concern at this time are a couple of weak layers in the mid snowpack, formed in late November and early December which can be found most notably at treeline, and may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect. These types of weak layers are typical failure planes, on which overlying slabs can start to slide and produce avalanches. 

Below, a variety of facet/crust layers from late October are buried near the bottom of the snowpack and are not active with respect to avalanche activity at this point in the season.

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.