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

North 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 -14.Wednesday: Cloudy with isolated flurries bringing a trace of new snow, increasing overnight. Light southwest winds. Alpine temperatures around -16.

Avalanche Summary

Reports from Saturday include observations of a skier triggered Size 1 wind slab on a south aspect at 2200 metres as well as smaller dry loose sluffs from steep, sheltered terrain. Reports from Friday included one skier-triggered Size 2 persistent slab avalanche from a steep, rocky feature on a west aspect at 2100m in the Monashees. The late November crust was indicated as its failure plane. 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

Last week's stormy weather brought 40-60cm of new snow to the region. Shifting winds have since 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 storm 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 another major feature in the snowpack and is down approximately 80-110cm at treeline 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 whumpfing and shooting cracks

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Wind Slabs

Shifting winds have been redistributing last week's storm snow into wind slabs on a variety of aspects. Ridge crests and crossloaded areas will be the most likely trigger points. Use extra caution at treeline where wind slab may overlie surface hoar

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

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