Avalanche Forecast

Issued: Apr 10th, 2017 3:56PM

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.

It is still winter in the alpine, and wind slabs and cornices continue to be the most likely problems.

Summary

Confidence

High -

Weather Forecast

Overnight: Overcast with light flurries and light southwest winds. Freezing down to 600 metres. Tuesday: 3-5 cm of new snow with light westerly winds and daytime freezing up to 1500 metres. Wednesday: Overcast with flurries and moderate southeast winds. Daytime freezing up to 1600 metres. Thursday: 5-10 cm of new snow with moderate southeast winds and daytime freezing up to 1700 metres.

Avalanche Summary

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.

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

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

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.

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

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 4

Valid until: Apr 11th, 2017 2:00PM