Avalanche Forecast

Issued: Feb 2nd, 2015 8:41AM

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.

rbuhler, Avalanche Canada

Northwest Inland.

Last week's storm snow appears to have stabilized but observations have been limited. A conservative approach is still recommended. The more recent snowfall may be forming new instabilities, especially in wind-loaded features.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Another 3-5mm of precipitation is expected Monday overnight in the south of the region. On Tuesday, light scattered flurries are expected to continue (2-4mm) with freezing levels at valley bottom and light SW winds in the alpine. Generally dry conditions are expected for Wednesday and Thursday but scattered flurries are possible in some areas. Freezing levels should stay at valley bottom and alpine winds should remain light. The next frontal system is currently forecast to reach the region on Thursday evening. Moderate precipitation is forecast for Friday through to at least Sunday.

Avalanche Summary

No new slab avalanches were reported on Sunday but sluffing from steep terrain was. On Saturday, a skier triggered a size 1 which released down 20-30cm. Natural activity up to size 3 was reported on Thursday and Friday during and following the storm. Skier triggering remains a concern for Monday but natural avalanches are generally not expected. Wind loaded features are my biggest concern for triggering but thin-spot triggering of persistent weakness would have the biggest consequences. Small avalanches also have the potential to step-down to a deeper weakness.

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. Continued light snowfall is adding to these mature storm slabs or possibly forming new thin storm slabs. 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 but I would keep it on my radar, especially in thin-snowpack areas, at higher elevations, and 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 potentially destructive layer. Possible triggers include thin spot triggering in high elevation terrain, a cornice fall, or a smaller avalanche stepping down.

Problems

Storm Slabs

Thick, old storm slabs may still be a concern. Thin, new storm slabs are more likely, especially in wind-loaded features. Small avalanches may have the potential to step-down to a deeper weakness.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - 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.

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

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 6

Valid until: Feb 3rd, 2015 2:00PM