Avalanche Forecast

Issued: Dec 24th, 2017 5:01PM

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

cgarritty, Avalanche Canada

South Columbia.

As storm snow settles, persistent slab problems emerge. Sheltered treeline elevations are a primary concern.

Summary

Confidence

High -

Weather Forecast

Monday: A mix of sun and cloud. Light northwest winds. Alpine temperatures around - 16.Tuesday: Mainly cloudy. Light southwest winds. Alpine temperatures around -15.Wednesday: Cloudy with isolated flurries bringing a trace of new snow, increasing overnight. Light southwest winds. Alpine temperatures around - 14.

Avalanche Summary

Reports from Saturday include a several observations of wind slab releases from Size 1-2. The Size 1 slabs were ski cut on varied aspects in the alpine. The Size 2 was at least a day old and was triggered naturally on a steep alpine face. 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. 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 early last week brought 50-80 cm of new snow to the region. Shifting winds over recent days have redistributed this storm snow into wind slabs on a variety of aspects at higher elevations while cold temperatures have worked to inhibit slab formation in wind-sheltered areas. The recent 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 are those that saw pronounced surface hoar development before the storm, particularly in sheltered areas at and below treeline. Recent snowpack tests show wide ranging reactivity at this interface but suggest that it may be most reactive on northerly aspects.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. Recent snowpack tests as well as an isolated avalanche report from the North Monashees suggests it may be coaxed into reacting in steep, variably loaded terrain features.

Problems

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.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Wind Slabs

Shifting winds have been redistributing storm snow into wind slabs on a variety of aspects. Northwest winds were the most recent. Exercise extra caution at lower elevations where winds may have formed a slab over a touchy surface hoar layer.

Be aware of variable wind loading patterns.Use ridges or ribs to avoid pockets of wind loaded snow.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 25th, 2017 2:00PM