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Avalanche Forecast

Archived

Jan 5th, 2020–Jan 6th, 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 unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Cariboos.

Recent snow and wind are out-pacing the snowpack's ability to adjust. Stay vigilant with simple terrain choices as this pattern continues.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Sunday night: Cloudy, 5-10 cm of snow, strong west winds, alpine temperature -10 C.

Monday: Mostly cloudy with isolated flurries, moderate west winds, alpine high temperature -8 C.

Tuesday: Cloudy, 5-10 cm of snow, moderate south winds, alpine high temperature -8 C.

Wednesday: Cloudy, 10-15 cm overnight and through the morning, moderate west winds, alpine high temperature -9 C.

Avalanche Summary

On Friday and Saturday there were reports of small to large (size 1.5-2.5) avalanches releasing from both natural and human triggers on a variety of aspects and elevations. Check out this MIN report and this MIN report for helpful illustrations of this problem. A few avalanches have also been remote-triggered, like this one observed Wednesday. Avalanche activity is beginning to reflect a distinction between smaller, wind-drifted slabs breaking within the storm snow versus larger slabs releasing on the late December surface hoar layer. 

Snowpack Summary

The most recent snow has been redistributed by strong winds in exposed areas, loading lee features with stiffer, more reactive slabs.

Over the past week, a total of 60-90 cm of snow has fallen burying a weak layer of feathery surface hoar and a hard melt-freeze crust on sun-exposed aspects. This layer has demonstrated reactivity past its due date as a storm slab interface, and it continues to produce large avalanches across aspects and elevations. Snowpack tests (check out this MIN report from Saturday) have also confirmed this weak layer's propagation potential.

There are a couple more deeply buried weak layers, including a surface hoar layer from mid-December and a facet/crust layer from late November. Despite the significant load from recent snowfall and wind as well as a widespread, large natural avalanche cycle, avalanches have not been observed stepping down to these layers.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be alert to conditions that change with elevation and wind exposure.
  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.

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.