Avalanche Forecast

Issued: Feb 17th, 2012 9:00AM

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

ghelgeson, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

A storm passes to the South of the region Friday night into Saturday, but the Purcells will be just on the edge of the system. As a result, only a few cm of snow are expected. Winds will be out of the SW Saturday at Moderate speeds, gusting strong. The freezing level is expected to remain near 1000m.Skies will remain overcast Sunday as a weak upper trough passes over the region. Freezing levels remain constant near 1000m and winds should be light out of the W, SW.

Avalanche Summary

A couple of size 3.0 avalanches were reported from the northern Purcells, one that stepped down to the ground around midway down the path. The other avalanche was on a cross loaded slope at about 2100 metres. These were reported as recent, but I am not sure of the occurrence date. No new avalanche observations were reported Thursday.

Snowpack Summary

Widespread surface hoar has been buried by a couple of cm of new snow in most of the region. A melt-freeze crust has developed on southerly aspects at all elevations. North and east aspects continue to have dry snow and some surface sloughing in steep terrain. Basal facets have not been reactive, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are suspect locations.

Problems

Wind Slabs

Forecast new snow and strong southwest wind are expected to develop windslabs in the alpine and at treeline.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 5

Cornices

Watch for tender cornices at ridge tops. They may be destructive by themselves, and have potential to trigger large avalanches on the slope below.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 5

Deep Persistent Slabs

Although a deep persistent slab would most likely require a large trigger, they are still possible; especially in thin snowpack areas or in unsupported, rocky terrain.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

3 - 7

Valid until: Feb 18th, 2012 9:00AM