Avalanche Forecast

Issued: Mar 26th, 2017 3:10PM

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

Avalanche Canada rbuhler, Avalanche Canada

Ongoing light snowfall and moderate winds Sunday night should continue to build wind slabs and cornices at higher elevations. Use extra caution on solar aspects and around cornices if the sun comes out Monday afternoon.

Summary

Confidence

Moderate -

Weather Forecast

3-6 cm of new snow is forecast for Sunday overnight with moderate southwest wind in the alpine. Another 5-10 cm is expected on Monday with light alpine wind and freezing levels reaching around 1500 m in the afternoon. Tuesday is expected to be mainly cloudy with sunny breaks in the morning and light snow in the afternoon. Alpine wind is forecast to be light to moderate from the southwest and freezing levels are expected to reach around 1500 m. Similar unsettled conditions are currently forecast for Wednesday with sunny breaks and light snowfall both possible.

Avalanche Summary

On Saturday, a natural cornice release triggered a size 2 storm slab on a north aspect at 2600 m and a size 1.5 wind slab was observed on a north aspect at 2500 m. Skiers and snowmobiles triggered several size 1 storm slabs and wind slabs, mainly on northwest through northeast aspects above 2000 m. Most of these recent slab avalanches were 20-40 cm thick but one was 50 cm thick and released on the mid-March crust. On Friday, small storm slabs were reactive to skier traffic on convex and wind loaded northerly aspects. The last avalanches to step down to deeper layers were on Thursday when explosives triggered cornices which pulled slabs 100-200 cm thick. On Monday, the recent storm snow is expected to be reactive at higher elevations, especially in wind loaded terrain and on steep convex features. Cornices are large and may become weak with daytime warming or during stormy periods. We are in a low probability, high consequence scenario for persistent slab avalanches failing on deep buried weak layers. Click here for more details. Click here for photos the avalanche cycle last week.

Snowpack Summary

20-50 cm of snow has now accumulated over the past week which overlies a rain crust below around 2000 m or a sun crust on solar aspects at higher elevations. Alpine wind has recently been strong mainly from south through west directions and has loaded leeward slopes in exposed terrain at treeline and in the alpine. Large cornices are also reported in the alpine. At lower elevations, there may be multiple crust layers in the upper snowpack which are now generally well bonded and stable. At higher elevations, the February weak layers are down 120-150 cm and woke up during last week's storm with many avalanches stepping down. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls also stepped down to these layers last week resulting in some very large full depth avalanches.

Problems

Wind Slabs

An icon showing Wind Slabs
Recent wind from south through west directions has redistributed the new storm snow in exposed terrain at higher elevations forming reactive wind slabs.
Use ridges or ribs to avoid pockets of wind loaded snow.Be alert to conditions that change with elevation.Use caution on steep open slopes and convex rolls

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
Sustained sun exposure or heavy triggers like a cornice falling could trigger deep, destructive avalanches on buried weak layers.
Use conservative route selection, choose moderate angled and supported terrain with low consequence.If triggered, wind slabs or cornices may step down to deeper layers resulting in very avalanches.Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Cornices

An icon showing Cornices
Cornices are large and may become weak with daytime warming, sun exposure, or during stormy periods.
Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.Give cornices a wide berth when travelling on or below ridges.Pay attention to overhead hazards like cornices.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 27th, 2017 2:00PM