Avalanche Forecast

Issued: Jan 18th, 2012 9:35AM

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

pgoddard, Avalanche Canada

Purcells.

Conditions in the alpine are variable across the region. Areas with minimal wind loading are MODERATE.

Summary

Confidence

Good - -1

Weather Forecast

Thursday: One more day of frigid cold to endure - although some minor warming may creep into the far south. Light winds. No precipitation.Friday: Light snow starting late in the day. Moderate south-westerly winds and temperatures rising slightly. Saturday: Continued light to moderate snowfall. South-westerly winds.

Avalanche Summary

A natural avalanche cycle to size 2.5 was reported on alpine slopes in the northern Purcells, failing in response to an overnight wind event. Skiers have been triggering soft slabs in steep terrain in the size 1-1 .5 range over the past few days, however many observers say that the snow remains mostly cohesionless due to the intense cold.

Snowpack Summary

20-45 cm of low density storm snow has been redistributed by mainly south-westerly winds. Cold temperatures have limited the widespread development of storm slabs, but wind slabs and cornices of variable reactivity have built up. Below the storm snow are various surfaces including facets, surface hoar in sheltered areas, wind crust, soft slabs and hard slabs. The mid-December surface hoar/facet persistent weakness, now down around 50cm on the eastern side of the range and as deep as 160cm on the western side, is still causing operators concern, especially in shallow snowpack areas. The consequences of a failure on this layer would be large. Facets and depth hoar exist at the base of the snowpack.

Problems

Wind Slabs

Wind slabs have formed recently, causing large avalanches in some areas. Be alert for wind slabs behind ridges and ribs, especially on east and north-facing slopes.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

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

Deep Persistent Slabs

Susceptible to human triggers particularly from thin spots on slopes with variable snow distribution, heavy impacts, or deep penetration. If triggered, slabs are likely to release across wide areas.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Jan 19th, 2012 8:00AM