Avalanche Forecast

Issued: Nov 21st, 2011 9:35AM

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

ccampbell, Avalanche Canada

Sea To Sky.

This bulletin is based on limited data. Local variation in conditions and danger levels are likely to exist. To produce more accurate forecasts, we need information. Please send an email to forecaster@avalanche.ca.

Summary

Confidence

Fair - Due to limited field observationsfor the entire period

Weather Forecast

Very heavy precipitation is expected overnight Monday into Tuesday, with over 100mm for coastal areas, before easing Tuesday Afternoon. Winds are expected to be strong to extreme southwesterlies during the height of the storm and freezing levels generally around 1500m could briefly rise as high as 1700m.Wednesday: Another 20-40cm of snow expected with freezing levels dropping down to 1000m and strong southwesterly winds.Thursday: Continued moderate to heavy precipitation with associated strong southwesterly winds, especially for coastal areas.

Avalanche Summary

I suspect widespread natural avalanche activity will occur overnight Monday into Tuesday during the height of the storm. Large avalanches from alpine and treeline elevations could run well below treeline.

Snowpack Summary

Newly formed surface hoar is now buried in many locations, particularly sheltered open treeline slopes. A rain crust with associated facets is generally down 50-80cm also has surface hoar crystals sitting on top and/or slightly below it. A deeper crust with associated facets and/or depth hoar is approximately 50cm off the ground. Recent snowpack tests on a northeast facing treeline slope gave moderate sudden results on both of these weaknesses.

Problems

Persistent Slabs

Particularly touchy where there is an associated rain crust, which is prominent between 1800m and 2050m.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

3 - 6

Wind Slabs

Near ridgecrests and terrain breaks, and in cross-loaded gullies. Heavy wind-loading is expected to cause widespread large avalanche activity.

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

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

2 - 5

Storm Slabs

Heavy loading from snow and rain is expected to cause widespread avalanche activity, particularly in immediate coastal areas.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Valid until: Nov 22nd, 2011 8:00AM