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Avalanche Forecast

Archived

Jan 7th, 2020–Jan 8th, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Cariboos.

Rapid loading from snow and wind on a reactive buried weak layer is creating very dangerous avalanche conditions. If triggered, avalanches could break deeper, propagate wider, and travel farther than anticipated. Travel in avalanche terrain is not recommended.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Tuesday night: Cloudy, 15-25 cm of snow, moderate to strong southwest wind, alpine temperature -7 C.

Wednesday: Cloudy, isolated flurries with trace accumulations, moderate west wind, alpine high temperature -10 C.

Thursday: Mix of sun and cloud, isolated flurries with trace accumulations, light west wind, alpine high temperature -12 C. 

Friday: Cloudy, 5-15 cm of snow, strong south wind, alpine high temperature -10 C.

Avalanche Summary

There have been many reports of large (size 2-2.5) avalanches from both natural and human triggers on a variety of aspects and elevations releasing on a surface hoar layer formed in late December. These avalanches have been breaking 80-120 cm deep. Several of them have been remote-triggered, like the one in this MIN from 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!

As the new snow settles, storm slab avalanches are likely to be triggered and have the potential to step down to these deeper layers, forming very large and destructive avalanches.

Snowpack Summary

20 to 35 cm of snow is forecast to accumulate by Wednesday afternoon with moderate to strong southwest wind. Expect storm slabs to be especially touchy in lee terrain features.

A very concerning layer of surface hoar from late December is now buried 80-120 cm deep. This layer formed in late December and continues to produce large avalanches across aspects and elevations. Recent snowpack tests have confirmed this weak layer's propagation potential (check out this MIN from Saturday).

Terrain and Travel

  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Choose simple, low-angle, well supported terrain without convexities.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.

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.