Avalanche Forecast

Issued: Jan 23rd, 2019 5:22PM

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

Avalanche Canada cgarritty, Avalanche Canada

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Our new snow is sitting over a nasty weak layer. The greatest concern is around wind-affected mid elevations where wind loading and buried surface hoar are most likely to coexist.

Summary

Confidence

Moderate -

Weather Forecast

Wednesday night: Mainly cloudy. Light southwest winds, increasing to strong northwest in the alpine.Thursday: A mix of sun and cloud. Light southwest winds, increasing to strong northwest in the alpine. Alpine temperatures starting around -9 and rising by a few degrees in the afternoon.Friday: A mix of sun and cloud. Strong northwest winds decreasing over the day. Alpine high temperatures around 0 as freezing levels rise to about 2000 metres.Saturday: Mainly sunny. Moderate to strong west winds. Alpine high temperatures around +3 with freezing levels reaching a possible 2900 metres.

Avalanche Summary

New snow was reactive on Sunday with several reports of skier-triggered, cornice-triggered, and natural avalanches. On Monday, explosives triggered size 2 storm slab avalanches and cornices. A weak layer of surface hoar buried 10-30 cm is responsible, especially around treeline 1500-1900 m. Most storm slab avalanches are reported on north-northeast aspects 1700-2000 m. However 2 recent avalanches occurred on southerly aspects. On Sunday, a size 2 avalanche released naturally around 2000 m on a southeast aspect with solar input with surprising propagation. On Monday, a snowboarder triggered a size 2 avalanche on a south aspect in open trees outside the Fernie boundary, fortunately with no injury. Two large snowmobile triggered avalanches were reported over a week ago. One was triggered on a thin, rocky, southwest facing feature near ridge crest north of Fernie (report here). The other was triggered on a wind affected south facing slope at treeline in the Corbin area (report here). Deep persistent slab activity has been most common in parts of the region with shallow snowpacks (such as near the continental divide) and alpine features with thin variable snowpack depths.

Snowpack Summary

Flurries with strong winds overnight brought recent snowfall accumulation to around 10-30 cm. In alpine and treeline areas, winds are redistributing storm snow loading lee terrain features and building cornices. Lower down, the recent snow is sitting over a weak layer of surface hoar and sun crusts. The surface hoar is most prominent around treeline elevations (1500-1900 m). On solar aspects and below treeline, the surface hoar and new snow overlie sun and temperature crusts.In shallow snowpack areas, the base of the snowpack may still be composed of weak faceted grains. In deeper snowpack areas, the middle and lower portions of the snowpack are generally considered to be well-settled and strong.

Problems

Persistent Slabs

An icon showing Persistent Slabs
A weak layer of surface hoar is buried under 10-30 cm recent snow, with deposits up to 50 cm deep in wind-loaded areas. This layer occurs with a crust on solar aspects and is most prevalent between 1500-1900 m.
Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Watch for signs of instability such as whumpfing, or cracking.Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Jan 24th, 2019 2:00PM