Avalanche Forecast

Issued: Nov 25th, 2011 9:21AM

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

Jlammers, Avalanche Canada

Sea To Sky.

Summary

Confidence

Fair - -1

Weather Forecast

Up to 30 cms of snow is expected for saturday accompanied by strong southwesterly winds. Freezing levels are expected to rise to 1500m. The system will continue through sunday bringing another 20-40 cms of snow. Winds are expected to remain strong but switch to north/northwest with freezing levels dropping to surface late in the day. A ridge should develop through sunday evening bringing mostly cold and clear conditions for monday.

Avalanche Summary

Explosives control in the region has produced numerous size 2 and 3 avalanches suspected to have stepped down to both of the facet/crust interfaces. Recent weather has limited the ability to make field observations, but there has probably been wide-spread natural activity as well due to recent snow and wind.

Snowpack Summary

The snowpack sits at approximately 150 cms just below treeline. At treeline and above, expect variable snow depths with much deeper wind deposits. In the lower snowpack there is a crust/ facet layer just above the ground that has been reactive to explosive testing in the region. In the mid snowpack, there has been widespread surface hoar observed at all elevations although reactivity on this layer seems to be decreasing. A more persistent weakness of facets with an associated crust can be found in the mid snowpack from 40-70 cms above the ground. This weakness exists at treeline and into the alpine where it is sensitive to human triggers and has a high propensity to propagate fractures. There's been over 120 cms of new snow since Sunday. Fluctuating freezing levels and varying wind and precipitation intensity during the recent storms has probably resulted in various storm snow weaknesses.

Problems

Persistent Slabs

Particularly touchy where there is an associated rain crust, which is prominent between 1800m and 2050m. Potential for remote triggering means that even low-angle terrain may not be safe if there is exposure from above.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 6

Wind Slabs

Newly formed weak wind slabs are likely lurking well below ridgecrests and terrain breaks, and in cross-loaded gullies.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

2 - 5

Storm Slabs

Any open slope with enough snow to smooth out ground roughness. Various weaknesses with and under the recent storm snow are likely sensitive to human triggers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

Explosives testing in the region has produced very large avalanches on this layer on unsupported, rocky terrain features

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 6

Valid until: Nov 26th, 2011 8:00AM