Avalanche Forecast

Issued: Feb 1st, 2015 8:33AM

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

jlammers, Avalanche Canada

Northwest Inland.

As snow accumulates on Monday, the Avalanche Danger will rise. Expect reactive new storm slabs to form.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Another pacific frontal system will bring snowfall to the coast on Monday. Lingering flurries are expected on Tuesday before a weak dry ridge of high pressure builds on Wednesday. Sunday night and Monday: Up to 15cm of snow / Strong southwest winds / Freezing level at valley bottom Tuesday: Very light snowfall and broken cloud / Moderate southwest winds / Freezing level at valley bottom Wednesday: Broken cloud / Moderate southwest winds / Freezing level at valley bottom

Avalanche Summary

Several storm slabs to size 2.5 were reported in the wake of Thursday night's storm. With more snow and wind on the way on Sunday night and Monday, I'd expect continued storm slab activity. It's important to keep in mind, a surface avalanche in motion may be what it takes to trigger deeper, more destructive persistent slab avalanches.

Snowpack Summary

Prior to the weekend, moderate to locally heavy snowfall and strong southwest winds built deep storm slabs which may still be reactive in wind-exposed terrain. More snow and wind forecast for Sunday night and Monday will add to this ongoing storm slab problem.About 70cm below the surface, you'll likely find a rain crust which was buried on January 26. Limited observations suggest the overlying slab may have a reasonable bond at this interface.A rain crust and/or surface hoar layer buried mid-January may be found at variable depths (in some areas over 100cm below the surface). This layer has reportedly gained significant strength, although I would keep it on my radar especially at higher elevations or in the far north of the region. Near the base of the snowpack is a crust-facet combination buried in November. This deep persistent weakness was recently reactive, and may still be touchy in the far north of the region. Wherever you are, I'd be cautious of this deep and destructive layer. Possible triggers include thin spot triggering in high elevation terrain, or a cornice fall.

Problems

Storm Slabs

New snow and wind on Sunday night and Monday will form new storm slabs. Watch for triggering in higher elevation, wind-exposed terrain.

Be cautious as you transition into wind affected terrain.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

In the mid snowpack there are a few crusts which may be reactive with the potential for large avalanches. Although less likely to trigger, these persistent weak layers may "wake-up" in response to a large trigger such as a cornice fall.

Make observations and assess conditions continually as you travel.>Be aware of the potential for large, deep avalanches due to the presence of buried crusts and/or surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Deep Persistent Slabs

Although less likely to trigger, recent avalanche activity suggests weak layers buried at the beginning of the winter should still be our radar, especially in the north of the region. Avalanches at this interface may reach their run-out zones.

Avoid convexities or areas with a thin or variable snowpack, especially in the north of the region.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Feb 2nd, 2015 2:00PM