Avalanche Forecast

Issued: Feb 2nd, 2015 8:30AM

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

rbuhler, Avalanche Canada

Northwest Coastal.

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. On Tuesday, light flurries are expected to continue (2-4mm) with freezing levels at valley bottom and light SW winds in the alpine. Light scattered flurries may continue on Wednesday morning but a weak ridge of high pressure is expected to build during the day and should keep things dry through midday Thursday. The next frontal system is currently forecast to reach the region on Thursday afternoon. Moderate-to-heavy precipitation is forecast for Friday through to at least Sunday.

Avalanche Summary

No new avalanches were reported on Sunday.Â On Saturday, a skier triggered a size 1 which released down 25cm.Â Natural avalanches to size 2.5 were reported on Thursday and Friday during and after the storm.Â Skier triggering remains a concern for Monday but natural avalanches are generally not expected.Â Wind loaded features are my biggest concern for triggering but thin-spot triggering of persistent weakness would have the biggest consequences.

Snowpack Summary

Prior to the weekend, moderate to heavy snowfall and strong southwest winds built deep storm slabs which are expected to be most reactive in wind-exposed terrain. Continued light snowfall is adding to these mature storm slabs or may be forming thin new slabs. About 100cm 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 up to 150cm below the surface). This layer is likely gaining strength, although I would keep it on my radar especially in thin snowpack areas and at higher elevations as it was the bed surface for much of the recent destructive avalanche activity. The November crust/ facet combo near the bottom of the snowpack is thought to be generally well bonded. However, this deep and destructive layer is still reported to be reactive in the far north of the region.

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.

Be alert to conditions that change with elevation.>Use ridges or ribs to avoid pockets of wind loaded snow.>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 alert to conditions that change with elevation.>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

3 - 5

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