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Avalanche Forecast

Archived

Jan 6th, 2020–Jan 7th, 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 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

Cariboos.

Snow, wind, and buried weak layers are keeping conditions complicated and dangerous. Stay vigilant with simple terrain choices as this pattern continues.

Confidence

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

Weather Forecast

Monday night: Partly cloudy with isolated flurries with trace accumulations, light west winds, alpine temperature -12 C.

Tuesday: Cloudy, 5-15 cm of snow, moderate south winds, alpine high temperature -8 C.

Wednesday: Cloudy, 10-20 cm overnight and throughout the day, moderate west winds, alpine high temperature -9 C.

Thursday: Mix of sun and cloud, isolated flurries with trace accumulations, light southwest winds, alpine high temperature -11 C. 

Avalanche Summary

There have been many reports of small to large (size 1.5-2.5) avalanches from both natural and human triggers on a variety of aspects and elevations. Most of these avalanches released on a surface hoar layer formed in late December. A few avalanches have been remote-triggered, like this one observed Wednesday. 

Be sure to check out this MIN, this MIN, and this MIN for helpful illustrations of slopes that are likely to harbor this problem. A sincere thanks to the community for submitting these reports!

Snowpack Summary

Recent snowfall has been redistributed by wind in exposed areas, loading lee features with stiffer, more reactive slabs.

Over the past week, a total of 70-100 cm of snow has accumulated burying a weak layer of feathery surface hoar and a hard melt-freeze crust on sun-exposed aspects. This layer formed in late December and continues to produce large avalanches across aspects and elevations. Snowpack tests have also confirmed this weak layer's propagation potential (check out this MIN from Saturday).

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Choose simple, low-angle, well supported terrain without convexities.
  • Be aware of the potential for large avalanches due to the presence of buried weak layers.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.