Avalanche Forecast

Issued: Feb 2nd, 2012 9:10AM

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

swerner, Avalanche Canada

Purcells.

Summary

Confidence

Good - -1

Weather Forecast

A strong ridge of high pressure will persist through the forecast period bringing dry conditions, sunny skies, and warmer temperatures. On Friday/Saturday freezing levels may rise to 1600m in the afternoon, then drop to valley bottom at night. Ridgetop winds should generally be light from the South. Maximum alpine temperatures near -1. Sunday brings alpine sun, valley cloud, and possibly temperature inversions.

Avalanche Summary

No new natural avalanche activity has been reported. On Tuesday two size 2 slab avalanches were reported in the Dogtooth range on Repeater Ridge. These occurred on a East aspect @2400m. On Monday explosive avalanche control done in the Dogtooth Range produced 2 avalanches up to size 2, running full depth to ground basal facets. These were on NW-N aspects, @ 2300m.

Snowpack Summary

Wind slabs are likely to be found on exposed areas at treeline, and above into the alpine. Storm slabs can be found at all elevations. They seem to be settling out quick, but still show sensitivity to rider triggers; especially on stepper slopes and convex rolls. Below this sits a pretty, well settled mid-pack. Yet, there are a few exceptions. The Jan. 13th SH/FC combo has been reactive in ski hill testing. Remember this is somewhat of a modified snowpack when compared to a true backcountry uncontrolled snowpack. Regardless, I feel like we can't take our eyes off this layer just yet, remember, it's only a couple weeks old.The mid December facet layer is buried approx. 80 cm on the east side and 200+ cm on the west side. This layer seems to have more energy in the Purcells than any other region in the province and was reactive on Jan. 28th, when a skier remotely triggered a size 3 avalanche. At this point we're looking at a low probability high consequence situation.There are basal facets at the ground which remain a concern, especially on Northerly aspects at high elevations. During the earlier part of the week a couple of slab avalanches have occurred, running down to these basal weaknesses. Snowpack depths at 2000m sit near 2m deep.

Problems

Wind Slabs

You're likely to find wind slabs on N-E facing aspects, below ridgecrests and lee of terrain features.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Storm Slabs

Storm slabs may be reactive to rider triggers, especially on steeper slopes and convex rolls. Use small test slopes with minimal consequence to see how reactive the storm slabs are.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 4

Persistent Slabs

Recent avalanche activity indicates that deeply buried weak layers are once again reactive. A skier, sledder or avalanche running in the storm snow could trigger a large avalanche, especially in steep rocky terrain.

Aspects: North, North East, East, South East, South.

Elevations: Alpine.

Likelihood

Possible

Expected Size

4 - 6

Valid until: Feb 3rd, 2012 3:00AM