Avalanche Forecast

Issued: Apr 12th, 2017 3:00PM

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

triley, Avalanche Canada

Cariboos.

Winter continues at higher elevations, watch for wind slabs and cornices that may be large and fragile.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Overnight: Moderate southeast winds, 3-5 cm of new snow, and freezing down to 800 metres. Thursday: 5-8 cm of new snow with moderate southeast winds and daytime freezing up to 1600 metres. Friday: Another 3-5 cm of new snow in the morning with light westerly winds and daytime freezing up to 1400 metres. Saturday: A few more cm of snow with light winds and a chance of scattered or broken cloud in the afternoon. Daytime freezing up to 1400 metres.

Avalanche Summary

Several natural cornice releases were reported up to size 2.5 on Tuesday. Explosive control produced cornice falls up to size 2.0 on Monday. Natural cornice falls up to size 2.5 were reported on Sunday from North aspects in the alpine between 2300-2400 metres.

Snowpack Summary

Recent moderate to strong winds redistributed new snow from the past few days into wind slabs on a range of aspects in the alpine and at treeline. These wind slabs have developed above a mix of old surfaces that include melt-freeze crusts below about 1900 metres and on solar aspects in the alpine. Fragile new cornice growth also developed along ridgelines over the course of the week. Below the new snow, a number of storm snow and crust layers that formed over mid to late March appear to be well bonded. The February weak layers are now down about 120-150 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 a concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.

Problems

Wind Slabs

Variable wind directions may have developed wind slabs on several aspects in the alpine and at treeline. Forecast new snow may make it difficult to locate these wind slabs. Forecast new snow may develop new wind slabs over the next few days.

Keep an eye out for reverse loading created by shifting winds.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

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.

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, Treeline.

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 resulting in large avalanches.Recognize and avoid avalanche runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

Valid until: Apr 13th, 2017 2:00PM