Avalanche Forecast

Issued: Feb 14th, 2017 4:40PM

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

jlammers, Avalanche Canada

Northwest Inland.

Sustained warming is set to undermine stability over the coming days. The scale of the impact is uncertain, but the strength of the snowpack is being tested

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Wednesday: 3-5 cm of new snow / Strong southwest winds / Freezing level at about 1100mThursday: 2-4 cm / Light and variable winds / Freezing level at about 1100mFriday: Light flurries / Light and variable winds / Freezing level at about 800m

Avalanche Summary

A MIN report from Sunday includes observations of recent Size 2 wind slab in the Hudson Bay area that is suspected to have run naturally on an east aspect. Perhaps more striking is the fact that the party also experienced several whumphs, suspected to be failures at one of our more shallow persistent weak layers. For Wednesday, expect recently formed wind slabs to be reactive to human triggering. Older hard slabs may be more stubborn, but also capable of much wider propagation. A storm focused on the north coast has brought modest new snow accumulations inland along with strong to extreme southwest winds that have promoted the formation of touchy new wind slabs in lee areas. Also keep in mind that a basal weakness continues to drive a low probability/high consequence deep persistent avalanche problem for the region. Very large avalanches remain possible, especially in shallow snowpack areas and as warm temperatures begin to penetrate deeper into the snowpack.

Snowpack Summary

A light snowfall over most 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 as well as a rain crust below about 1400 m. The new snow will contribute to wind slab formation in wind exposed areas while covering faceted surface snow as well as surface hoar in more sheltered areas. 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 has recently been considered dormant but it may become active once again with sustained warming over the coming days. It may also be possible for a smaller avalanche to 'step down' to this layer.

Problems

Wind Slabs

Last week's outflow winds have shifted to a strong southwest flow, coupled with light accumulations of new snow. The changed pattern leaves us with a mix of touchy new wind slabs along with older, more stubborn hard slabs on a wide range of aspects.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be cautious as you transition into wind affected terrain.Be aware of the potential for wide propagations due to the presence of hard windslabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

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 remain elevated while warm temperatures persist.

Avoid steep convexities or areas with a thin or variable snowpack.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Loose Wet

Rain and moist snow accumulating at lower elevations will promote loose wet avalanches on Monday, especially in steep terrain. This problem will present at higher elevations as the freezing level rises.

Use extra caution on slopes if the snow is moist or wet.Be cautious of sluffing in steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Valid until: Feb 15th, 2017 2:00PM