Avalanche Forecast

Issued: Mar 24th, 2017 3:36PM

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

Avalanche Canada rbuhler, Avalanche Canada

Tricky conditions are expected to persist at higher elevations with new snow and wind building slabs as well as the continuing possibility of avalanches releasing on deep weak layers. Conservative terrain selection remains highly recommended.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Saturday

Weather Forecast

5-10 cm of snowfall is expected Friday overnight with moderate to strong southwest wind in the alpine and freezing levels around 1000 m. Another 3-6 cm is expected on Saturday with the possibility of sunny breaks in the afternoon. Alpine wind is forecast to be moderate from the southwest and freezing levels are expected to reach around 1400 m. On Sunday, a mix of sun and cloud is expected with light alpine wind and freezing levels reaching around 1600 m. Mainly cloudy conditions are forecast for Monday with light snow flurries.

Avalanche Summary

On Thursday, a natural size 2 avalanche was reported on a southeast aspect at 2600 m. Skiers triggered a couple size 1 storm slabs on northwest and east aspects at 2100 m which were 20-25 cm thick. No new avalanches were observed on Wednesday. On Tuesday, a size 3 cornice released on a northeast aspect at 2800 m scrubbed down to rock and a size 2.5 storm slab released on a north aspect at 1900 m. Explosives released a cornice on a north aspect which triggered a size 3.5 deep persistent slab which stepped down to the November crust and to the ground in places. Explosives also released a size 2 cornice with a small slab and a size 2.5 persistent slab on a south aspect which failed on the mid-February crust layer down 120 cm. On Saturday, storm slabs are expected to be reactive at higher elevations, especially in wind loaded terrain and on steep convexities. 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 buried weak layers. Click here for more details. Click here for photos of the recent large avalanche cycle.

Snowpack Summary

15-30 cm of new snow overlies a rain crust at lower elevations 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 and expected to be biggest on northerly aspects in the alpine. The mid-March crust is down 40-60 cm in the south of the region and shallower in the north. The mid-February crust/facet layer is now typically down 100-150 cm and has recently been reactive with many avalanches stepping down to it. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches stepped down to these layers recently resulting in very large avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs
Ongoing incremental loading is building slabs which may sit over a rain crust or sun crust. These slabs are most reactive in wind loaded terrain.
Be alert to conditions that change with elevation.Use ridges or ribs to avoid pockets of wind loaded snow.Use caution on steep open slopes and convex rolls

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
Various persistent weaknesses throughout the snowpack create the potential for avalanches stepping down to buried weak layers. Sustained sun exposure or heavy triggers like a cornice falling could trigger deep, destructive avalanches.
If triggered, storm slabs or cornices may step down to deeper layers resulting in large avalanches.Use conservative route selection, choose moderate angled and supported terrain with low consequence.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 during the heat of the day or during a storm.
Cornices become weak with daytime heating. Give cornices a wide berth when traveling on ridges.Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

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