Avalanche Forecast

Issued: Apr 11th, 2017 4:07PM

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

North Columbia.

Winter continues in the alpine. A new series of storms is forecast over the next few days. Watch for new wind slabs developing.

Summary

Confidence

High -

Weather Forecast

Overnight: Broken skies or scattered cloud with moderate southeast winds developing and freezing down to 500 metres. Wednesday: Overcast with moderate southeast winds and 3-5 cm of new snow in the afternoon. Daytime freezing up to 1500 metres. Thursday: Overcast with 5-8 cm of new snow and a chance of convective flurries producing up to 15 cm in some areas. Daytime freezing up to 1600 metres. Friday: Mostly cloudy with a chance of sunny breaks. Expect a few flurries combined with light winds and daytime freezing up to 1400 metres.

Avalanche Summary

No new avalanches reported on Monday. One Bergschrund collapsed on a north aspect at 2700 metres. Natural cornice falls and a couple of natural wind slabs size 2.0 were reported on Sunday. Some sluffing continues to be reported from steep shaded alpine terrain.

Snowpack Summary

The recent storm snow is now 30-60 cm including the snow from the end of last week. The recent snow buried a mix of old surfaces that include melt-freeze crusts at treeline and below and on solar aspects in the alpine. Fragile new cornice growth also occurred along ridgelines over the course of the week. 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. 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

Wind Slabs

Variable wind directions over the past few days have developed wind slabs on several aspects in the alpine and at treeline. Forecast new snow may hide recent pockets of wind slab.

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: Alpine, Treeline.

Likelihood

Possible - Likely

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.

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

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, slab avalanches or cornices may step down to deeper layers.Recognize and avoid avalanche runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

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