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Avalanche Forecast

Archived

Jan 9th, 2020–Jan 10th, 2020

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

Regions

Cariboos.

A couple of problems are in play for the region. Seek sheltered terrain to avoid wind slabs and use careful snowpack evaluation and low consequence terrain to assess and manage the problematic persistent weak layer

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Forecast snowfall amounts are uncertain.

Weather Forecast

Thursday night: Mostly cloudy, isolated flurries with trace accumulations, light to moderate southwest wind, alpine temperature -16 C. 

Friday: Cloudy, 10-25 cm of snow, strong south wind, alpine high temperature -10 C.

Saturday: Cloudy, 5-15 cm of snow, moderate southwest wind, alpine high temperature -10 C.

Sunday: Cloudy, 5-15 cm of snow, light south wind, alpine high temperature -18 C.

Avalanche Summary

In the aftermath of the recent storm, there have been several reports of very large (size 3) avalanches from both natural and human triggers releasing on a surface hoar layer formed in late December. These avalanches have been breaking 60-120 cm deep. 

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!

Freshly formed wind slabs on Friday are expected to be reactive to human triggering and will have the potential to step-down to this deeper layer, forming very large and destructive avalanches.

Snowpack Summary

Low density snow will begin to accumulate tomorrow afternoon with 10-25 cm possible. Strong south winds will likely drift this new snow into stiffer slabs on lee terrain features at higher elevations, especially near ridge crests.  

The most recent storm delivered 15-35 cm of snow across the region with southwest winds. Higher accumulations fell in the southern and eastern parts of the region. The storm snow loaded a concerning layer of surface hoar from late December, which is now buried 60-120 cm deep. Recent snowpack tests have confirmed this weak layer's propagation potential, and this layer continues to produce large avalanches across aspects and elevations. 

Terrain and Travel

  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.