Avalanche Forecast

Issued: Feb 13th, 2018 4:14PM

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

cgarritty, Avalanche Canada

South Coast.

Touchy new storm slabs are expected to form over Tuesday night. Wind affected areas where new snow will fall on firm crust are the most concerning.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Tuesday night: Periods of snow bringing approximately 20 cm of new snow. Moderate to strong southwest winds.Wednesday: A mix of sun and cloud with clearing over the day. Light to moderate northeast winds. Freezing level rising to 900 metres with alpine high temperatures of -3.Thursday: Mainly cloudy with cloud and light flurries increasing over the day. About 5 cm of new snow accumulating by Friday morning. Light southwest winds, increasing overnight. Freezing level to 500 metres with alpine high temperatures of -4.Friday: A mix of sun and cloud. Light to moderate northwest winds. Freezing level to 900 metres with alpine high temperatures around -2.

Avalanche Summary

On Saturday, a cornice collapse was the likely cause of a size 2 avalanche on a north facing slope near the West Lion. See here for images and more details. Looking forward, avalanche danger will increasing quickly over Tuesday night as new storm slabs form over the firm crust that exists at most elevations. This crust is likely to act as a very effective sliding layer that will resist bonding to the new snow over the near term. Treeline elevations may see the touchiest conditions develop because of the combination of this crust with the added factor of winds promoting slab formation.

Snowpack Summary

Increasing flurries are expected to bring about 20 cm of new snow to the region by Wednesday morning. Beneath the new snow, the upper snowpack at most elevations has locked up as a firm rain crust. In the high alpine, the new snow is accumulating over wind affected surfaces and thin wind slabs. It will take time for the new snow to form a solid bond with these varied surfaces - especially the rain crust. The average snowpack depth at treeline is 300 cm of well settled snow with no significant layers of concern.

Problems

Storm Slabs

Up to 20 cm of new snow is expected to fall overnight and form fresh storm slabs at all elevations. The new snow will fall on a hard rain crust at all but high alpine elevations and it is not expected to bond well.

Watch for signs of instability such as cracking and recent avalanches.Expect to find increasingly touchy slabs on the surface as you enter wind affected terrain.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely - Certain

Expected Size

1 - 2

Cornices

Large cornices have formed and will be building weak new growth over Tuesday night. Cornices are inherently unstable, unpredictable, and demand respect. Give them a wide berth from above and below.

Firm cornices may pull back into flat terrain at ridgetop if they fail.Give cornices a wide berth when traveling on or below ridges.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Feb 14th, 2018 2:00PM