Avalanche Forecast

Issued: Feb 1st, 2012 10:13AM

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

Fair - Freezing levels are uncertain for the entire period

Weather Forecast

Wednesday the region may have seen the last drips and drabs of precipitation for a while. A strong ridge building from the western part of the province will bring dryer conditions for the forecast period. On Thursday ridgetop winds will be light from the NW; freezing levels may rise to 1200m and alpine temperatures steady near -5. Friday and Saturday the ridge of high pressure holds true with freezing levels potentially reaching 1800m.

Avalanche Summary

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

The Purcell region hosts a complex and variable snowpack right now.Up to 40cms of storm snow fell over the weekend. This new snow was accompanied by moderate to strong winds from the SE-SW. 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. Reports indicate these slabs are touchy; especially to rider triggers. This new snow fell on a snow pack that is for the most part, pretty well settled. 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 snwpack 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 two weeks old.It sounds like there is a lot of strong snow over the mid December facet layer which 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

New snow and winds blowing from all directions have formed wind slabs on most slopes. You're likely to find the bigger wind slabs on N-E facing aspects but you need to be suspect of all open slopes at and above treeline.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Storm Slabs

Storm slabs are still reactive to rider triggers, especially on steeper slopes and convex rolls. It may take a few days for the storm snow to settle out. Use small test slopes with minimal consequence to see how reactive the storm slabs are.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

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 2nd, 2012 3:00AM