Avalanche Forecast

Issued: Dec 23rd, 2017 4:53PM

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

cgarritty, Avalanche Canada

South Columbia.

Slab formation remains the critical factor for avalanche danger under current conditions. The best and safest riding will be in soft, unconsolidated snow.

Summary

Confidence

Moderate -

Weather Forecast

Sunday: A mix of sun and cloud. Light west winds. Alpine temperatures around -14.Monday: Mainly cloudy. Light northeast winds. Alpine temperatures around -17Tuesday: A mix of sun and cloud. Light southwest winds. Alpine temperatures around -17.

Avalanche Summary

Reports from Friday included observations of numerous wind slab releases, mainly Size 1, with a couple of Size 2. These were initiated by a mix of natural and skier triggers on varied aspects above 2000 metres. Persistent slab activity to Size 1 was also reported at lower elevations. Reports from the previous few days included explosives controlled and natural storm snow avalanches to size 2.5 in the alpine and treeline. There were also several reports of skier accidental and skier remote (triggered from a distance) avalanches to size 1.5 at and below tree line. Persistent slab avalanche danger can be expected to persist in areas where our recent snow consolidates into a slab above the December 15 interface. In areas where new snow has not yet consolidated into a slab, expect continued potential for triggering loose dry avalanches in steep terrain.

Snowpack Summary

Stormy weather over the past week has brought 50-80 cm of new snow to the region. The new snow lies over a wide variety of old surfaces, including large surface hoar (weak, feather-like crystals), hard crusts formed by sun or wind, and sugary facets. The bond at this old snow interface is of critical importance in areas where the overlying snow has consolidated into a slab. The most concerning areas areas will be those that have seen previous surface hoar development, such as sheltered areas at and below tree line and sheltered northerly aspects in the alpine. Additionally, any steep solar aspects where surface hoar may be sitting on sun crust should be considered areas where this weak layer may be more likely to trigger. A crust which was formed by rain in late November is a major feature in the snowpack and is down approximately 90-120cm at tree line elevations. Snowpack tests suggest the snow above is currently bonding well to it.

Problems

Wind Slabs

Shifting winds since the storm have been redistributing new snow into wind slabs on a variety of aspects. The freshest slabs are the result of recent northerly winds. Keep this reverse loading pattern in mind as you gain elevation.

Use ridges or ribs to avoid pockets of wind loaded snow.Be aware of areas that have been reverse loaded by winds.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

The December 15 interface will likely be most reactive where the new snow has settled into a slab over buried surface hoar. Use extra caution around steeper, sheltered slopes at treeline and below - especially if you see signs of slab formation.

Watch for signs of slab formation, such as whumphing or shooting cracks.Buried surface hoar is more likely to be preserved in sheltered openings at and below tree line.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Dec 24th, 2017 2:00PM