Avalanche Forecast

Issued: Jan 25th, 2019 5:01PM

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

Avalanche Canada cgarritty, Avalanche Canada

The intensity of warming is uncertain, and so is its potential impact on our buried weak layer. Sun exposed wind slabs and large loose wet sluffs could be triggers for this layer, and mid elevations are the most likely places to find it preserved.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Friday night: Mainly cloudy. Light southwest winds, increasing to strong northwest in the alpine. Saturday: Mainly cloudy with a chance of isolated flurries and a trace of new snow. Light southwest winds, increasing to strong northwest in the alpine, extreme overnight winds. Alpine high temperatures around 0 with a strong chance of an alpine temperature inversion bringing alpine temperatures well above freezing.Sunday: Cloudy with sunny periods. Strong to extreme northwest winds easing over the day. Alpine temperatures falling from around 0 to -6 as freezing levels decline from 2000 to 1000 metres.Monday: Mainly sunny. Light variable winds. Alpine high temperatures around -8.

Avalanche Summary

Avalanche observations from Wednesday were limited to smaller (size 1-1.5) loose dry sluffs and small slabs releasing naturally from steep alpine features.On Monday, explosives triggered size 2 storm slab avalanches and cornices. Our 10-30 cm-deep weak layer of surface hoar was the failure plane.Skier-triggered, cornice-triggered, and natural storm slab avalanches were reported mainly on north-northeast aspects from 1700-2000 m over the weekend, including 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

10-30 cm of badly wind-affected snow forms the current snow surface, the product of snowfall this past weekend and more recent strong and shifting winds. In alpine and treeline areas, winds have been redistributing this 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) and is an increasing concern during the warming forecast in our region. 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.
Moist sluffs from sun-exposed slopes may act as a trigger for slabs in the afternoon.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 - Likely

Expected Size

1 - 2

Wind Slabs

An icon showing Wind Slabs
Strong, shifting winds have been redistributing loose snow into wind slabs at all elevations. Analyze slopes for patterns of wind redistribution and steer clear of wind loaded pockets and thinner areas adjacent to them.
If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Sun exposed, moist surface snow on steep slopes will be likely to produce loose wet sluffs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 26th, 2019 2:00PM