Avalanche Forecast

Issued: Mar 26th, 2017 3:20PM

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

Wind slabs are expected to remain touchy at higher elevations. Deeply buried weak layers continue to be reactive and produce sporadic large avalanches.  Use extra caution on solar aspects and around cornices if the sun comes out on Monday afternoon.

Summary

Confidence

Moderate -

Weather Forecast

2-4 cm of new snow is forecast for Sunday overnight with moderate southwest wind in the alpine. Another 2-4 cm is expected on Monday morning with light alpine wind. Sunny breaks are forecast for the afternoon with freezing levels reaching around 1700 m. 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 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

A natural size 3 persistent slab was observed on Saturday northwest of Valemount on a north aspect at 2500 m which failed down 50-100 cm. On Friday, a natural size 3.5 avalanche was reported southwest of Valemount on a east aspect at 2600 m. It's not certain how old it was, but it was likely triggered by a cornice or ice fall, stepped down to ground, and destroyed some mature timber. Earlier last week, several size 2.5-3.5 avalanches were triggered naturally and by explosives. This included a natural cornice triggered size 3 avalanche on a northeast aspect, an explosive triggered size 3.5 deep persistent slab that stepped down to the November crust, and a explosive triggered size 2.5 persistent slab that failed on the mid-February crust layer down 120 cm.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

20-40 cm of snow has now accumulated over the past week which 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 in the alpine. At lower elevations, there may be multiple crust layers in the upper snowpack which are now expected to generally be well bonded and stable. At higher elevations, the February crust/facet layer is down 100-150 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 recently resulting in some very large full depth avalanches. Heavy triggers like cornices and explosives continue to sporadically trigger deep weaknesses in the snowpack as recently as Saturday.

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.
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: 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.
If triggered, wind 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 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