Avalanche Forecast

Issued: Apr 13th, 2017 3:00PM

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.

Avalanche Canada triley, Avalanche Canada

New storm slabs have developed at higher elevations. Changing winds may result in reverse loading.

Summary

Confidence

Moderate - Wind speed and direction is uncertain on Friday

Weather Forecast

Overnight: 5-8 cm of new snow with moderate west winds and freezing down to 800 metres. Friday: Overcast with another 3-5 cm of snow combined with moderate west winds and daytime freezing up to 1600 metres. Saturday: Overcast with flurries and moderate west winds and daytime freezing up to 1300 metres. Sunday: Mostly sunny with light winds and daytime freezing up to 1800 metres.

Avalanche Summary

Two deep persistent natural avalanches size 3.5 were reported on Wednesday with fractures that were about 4 metres deep. The december surface hoar weak layer is expected to be the sliding layer. Natural avalanches up to size 3.0 were reported on Tuesday on south thru west aspects in the alpine, it was not mentioned if they were cornice triggered.

Snowpack Summary

The new storm slab is 20-30 cm deep and arrived with east or southeast winds in most areas. The winds are forecast to change to the west, and this may result in some reverse loading and new wind slabs on several aspects. This new snow is sitting on another 30-60 cm of recent snow from the past week. The recent snow buried a mix of old surfaces that include melt-freeze crusts on all aspects at treeline and below, and on solar aspects in the alpine. Cornices are reported to be large and fragile, and reports of natural cornice falls continue on a regular basis. The February weak layers are now down about 170-220 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers produced large avalanches with cornice falls and other heavy triggers in late March and early April. They remain an ongoing concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.

Problems

Storm Slabs

An icon showing Storm Slabs
Forecast new snow and wind may develop storm slabs in the alpine and at treeline. Watch for reverse loading if the winds change from east to west. Rain at lower elevations may result in loose wet avalanches.
Use ridges or ribs to avoid pockets of wind loaded snow.Keep an eye out for reverse loading created by shifting winds.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Cornices

An icon showing Cornices
Cornices have grown large and may fall off naturally with solar effect 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, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Persistent Slabs

An icon showing Persistent Slabs
A couple of natural deep persistent slab avalanches size 3.5 were reported on Wednesday that were 400 cm deep. Deep persistent avalanches are more likely on solar aspects when the sun is out and solar radiation is strong.
If triggered, slab avalanches or cornices may step down to deeper layers.Recognize and avoid avalanche runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 4

Valid until: Apr 14th, 2017 2:00PM