Avalanche Forecast

Issued: Apr 11th, 2017 4:54PM

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

triley, Avalanche Canada

Purcells.

Stormy weather is forecast for the next few days. Expect new wind slabs to develop and watch for reverse loading if the wind is out of the East.

Summary

Confidence

High -

Weather Forecast

Overnight: Cloud and moderate southeast winds developing with freezing down to 800 metres. Wednesday: 3-5 cm during the day with moderate southeast winds and daytime freezing up to 1600 metres. Thursday: 5-15 cm by morning, with the heaviest amounts in the south of the region. Daytime freezing up to 1800 metres. Friday: Another few cm of new snow with light winds and daytime freezing up to 1400 metres.

Avalanche Summary

Explosive control and natural triggers released cornices up to size 3.0 in the central part of the region on Monday. One cornice failed during explosives control when the shot was dropped onto the cornice structure resulting in a size 2.0 that did not release a slab on the slope below.

Snowpack Summary

Recent moderate to strong winds have redistributed new snow into wind slabs on a range of aspects at higher elevations. Fragile new cornice growth also occurred along ridgelines over the course of the week. The new snow has buried melt-freeze crusts on all aspects below about 2200 metres and in the high alpine on solar aspects. Isolated surface hoar may be found below the new snow on shaded aspects at high elevations. Below the new snow interface, a number of storm snow and crust layers that formed over mid to late March appear to be well bonded. At higher elevations, the February crust/facet layer is now down around 130-150 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These layers were active during a storm in mid-March and produced some very large avalanches. Occasional deep releases were also reported in late March and early April, keeping these layers an ongoing concern.

Problems

Wind Slabs

Wind slabs have developed on several aspects over the past few days. Forecast new snow may make it difficult to observe these recent wind slabs.

Keep an eye out for reverse loading created by shifting winds.Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Cornices have grown large and may break off naturally due to solar exposure or daytime warming. Cornice falls were responsible for triggering a number of large persistent slab avalanches last week.

Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.Avoid travel on slopes that are exposed to cornices overhead.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3

Persistent Slabs

A cornice fall or smaller slab avalanche currently has the potential to trigger large, destructive avalanches on deeply buried weak layers. This is more likely to occur in thin or variable snowpack areas at higher elevations.

If triggered, wind slabs or cornices may step down to deeper layers and result in large avalanches.Recognize and avoid avalanche runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 4

Valid until: Apr 12th, 2017 2:00PM