Avalanche Forecast

Issued: Jan 21st, 2012 10:34AM

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

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Sunday: 5-8cm of snow / Moderate westerly winds / Freezing level at surfaceMonday: Light snowfall / Moderate westerly winds / Freezing level at surfaceTuesday: Moderate snowfall / Strong southwest winds / Freezing level at surface

Avalanche Summary

Recent observations include loose snow avalanches running in steep terrain and isolated skier-triggered wind slabs in the size 1-2 range. Avalanche activity slowed down towards the end of the week, but is expected to increase again in the wake of Friday night/Saturday's storm.

Snowpack Summary

New storm snow from friday night/saturday morning has built up over wind slabs in exposed features and over loose dry snow in sheltered areas. New snow amounts from friday's pulse were highly variable throughout the region. Lesser 24hr snowfall amounts were at about 6-10cm on the east side, and up to 25cm on the west side. Anomalous southeast moderate winds were observed in Golden, so expect irregular loading patterns at ridge top in that area. The mid-December surface hoar/facet persistent weakness, now down around 55cm on the eastern side of the range and as deep as 190cm on the western side, is still causing operators concern, especially in shallow snowpack areas. Recent snowpack tests show moderate to hard, sudden planar results on this layer. The consequences of a failure on this layer would be large. Facets and depth hoar exist at the base of the snowpack. Cornices are large and weak in some areas.

Problems

Wind Slabs

Moderate winds from saturday will have created touchy windslabs on lee features at higher elevations.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Storm Slabs

A classic recipe for storm slabs has evolved; particularly on the west side of the range: new snow falling with rising temperatures onto loose dry snow. Watch for deeper storm slab avalanches, especially in steep or convex terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 5

Persistent Slabs

Two layers to watch: 1. Buried surface hoar, most likely triggered on steep, unsupported slopes amongst the trees. 2. Basal facets, triggerable from thin snowpack areas or by a very heavy load (cornice fall, airborne sled). Avalanches could be large.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

4 - 7

Valid until: Jan 22nd, 2012 8:00AM