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Avalanche Forecast

Archived

Mar 5th, 2020–Mar 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 unlikely, human triggered possible.
Treeline
Natural avalanches possible, human triggered probable.
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.

Regions

Cariboos.

Strong winds and new snow have formed reactive wind slabs at upper elevations. A buried weak layer continues to surprise riders and warrants a conservative mindset and terrain use strategy.

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Thursday night: Cloudy, convective flurries with up to 5 cm of snow, strong southwest winds decreasing to moderate, alpine temperature -10 C, freezing level dropping to valley bottom.

Friday: Mix of sun and cloud, isolated flurries with trace accumulations, light southwest winds, alpine high temperature -6 C, freezing level 600 m.

Saturday: Mostly cloudy, isolated flurries with trace accumulations, light variable winds, alpine high temperature -7 C, freezing level at valley bottom.

Sunday: Mix of sun and cloud, isolated flurries with trace accumulations, light southwest winds, alpine high temperature -7 C, freezing level at valley bottom.

Avalanche Summary

Over the past several days, there has been a natural cycle of large to very large (size 2-3) avalanches releasing in the recent storm snow, primarily on northeast, east, and southeast aspects above 1800 m. Several were triggered by large cornices failures. 

Over the past week, there have been many reports of persistent slab avalanches releasing on the Feb 22 surface hoar. These avalanches primarily occurred on north, northeast, and east aspects between 1400-2100 m. Check out this MIN for a helpful illustration of where you might expect to find this problem. 

Snowpack Summary

Incremental snowfall and strong winds continue to build wind slabs in the alpine and open areas at treeline. A few sun crusts exist on solar aspects in the upper snowpack. Convective snowfall in the wake of the storm may obscure the evidence of these wind slabs.

A weak layer of surface hoar may be found 60-100 cm deep. There is uncertainty about the distribution and reactivity of this layer, especially in the north of the region. Sheltered slopes near and below treeline are most suspect. Read more about surface hoar on our forecaster blog! 

Below a melt-freeze crust down 80-120 cm from early February, the snowpack is well settled and strong.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Use conservative route selection and resist venturing out into complex terrain.
  • Even brief periods of direct sun could produce natural avalanches.

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.