Avalanche Forecast

Issued: Feb 11th, 2017 3:58PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Deep Persistent Slabs.

Avalanche Canada cgarritty, Avalanche Canada

Changing weather has added complexity to our wind slab problem. Rising freezing levels early this week may coax our persistent slab problem into action.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Sunday: Mainly cloudy with flurries bringing up to 10 cm of new snow. Extreme southwest winds. Freezing level rising to 1000 metres with alpine temperatures of -3.Monday: Mainly cloudy with isolated wet flurries and a trace of new snow. Winds strong to extreme from the southwest. Freezing level rising to 1900 metres with alpine temperatures of +1.Tuesday: Mainly cloudy with isolated wet flurries and a trace of new snow. Winds strong to extreme from the southwest. Freezing level to 2100 metres with alpine temperatures of +3.

Avalanche Summary

No new avalanches have been reported in the past few days. Our most recent avalanche activity was reported last weekend and included a remotely triggered Size 2 avalanche as well as naturally triggered avalanches to Size 2.5. Some of the natural avalanches involved the full depth of the snowpack.For Sunday, expect recently formed wind slabs to be reactive to human triggering. Older hard slabs will be more stubborn, but also capable of much wider propagation. A storm currently impacting the north coast should bring modest new snow accumulations inland along with strong to extreme southwest winds that will promote new wind slab formation in lee areas. A basal weakness continues to drive a low probability/high consequence problem for the region. Very large avalanches remain possible, especially in shallow snowpack areas.

Snowpack Summary

A light snowfall in some parts of the region has given a thin cover to the widespread wind affected surfaces recently reported in exposed terrain. This includes scoured surfaces, sastrugi, and hard wind slabs. The new snow will contribute to wind slab formation in wind exposed areas. In areas sheltered from the wind, new snow has begun to cover faceted surface snow as well as surface hoar. Below around 1400 m elevation, a rain crust can be expected beneath the new snow. Deeper in the snowpack, several buried surface hoar layers can be found between 30-70 cm deep. Recent reports suggest these layers have generally stabilized but isolated weaknesses may still exist, especially where buried surface hoar is still intact. A generally stiff mid pack sits above weak sugary snow near the ground. This basal weakness woke up during the last storm and produced numerous large avalanches which released on the ground. The layer is dormant for the time being but is expected to wake up with warming, heavy loading, or by the weight of a smaller avalanche stepping down.

Problems

Wind Slabs

An icon showing Wind Slabs
Strong outflow winds have shifted to a strong southwest flow, coupled with light accumulations of new snow. The changing pattern leaves us with a mix of touchy new wind slabs along with older, more stubborn hard slabs on a wide range of aspects.
Be aware of the potential for wide propagations due to the presence of hard windslabs.Be cautious as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
A weakness at the bottom of the snowpack is lingering and may be triggered in shallow snowpack areas or by the weight of smaller avalanches. The potential for a deep release on this layer will increase with rising freezing levels.
Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Feb 12th, 2017 2:00PM

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