Avalanche Forecast

Issued: Apr 12th, 2017 3:11PM

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

triley, Avalanche Canada

Purcells.

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

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Overnight: 5-10 cm of new snow with moderate southeast winds and freezing down to 1000 metres. Thursday: 3-5 cm of new snow with winds becoming moderate southwest. Daytime freezing up to 1800 metres. Friday: Another 3-5 cm of new snow with moderate westerly winds and daytime freezing up to 1400 metres. Saturday: A few more cm of new snow with moderate southwest winds and a chance of sunny breaks in the afternoon. Daytime freezing up to 1400 metres.

Avalanche Summary

Natural cornice falls to size 2.0 and explosives control to size 3.0 were reported from the central part of the region on Tuesday. 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

Storm Slabs

Forecast new snow and wind may develop storm slabs in the alpine and at treeline. Rain at lower elevations may result in loose wet avalanches.

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: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

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 13th, 2017 2:00PM