Avalanche Forecast

Issued: Apr 11th, 2017 4:24PM

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

South Columbia.

Winter continues in the alpine. A series of new storms are expected to develop new wind slabs over the next few days.

Summary

Confidence

High -

Weather Forecast

Overnight: Cloud and moderate southeast winds developing with freezing down to 700 metres. Wednesday: 5-8 cm of new snow with moderate southeast winds and daytime freezing up to 1600 metres. Thursday: 5-10 cm of new snow with a chance of convective flurries producing up to 15 cm in some areas. Daytime freezing up to 1700 metres. Friday: Mostly cloudy with a chance of sunny breaks in the afternoon and daytime freezing up to 1400 metres.

Avalanche Summary

Natural cornice falls were reported up to size 3.0 on Monday. There were also reports of isolated wind slabs up to size 1.0. Loose dry and loose wet avalanches to size 1.0 were reported on Sunday.

Snowpack Summary

The recent storm snow is 30-50 cm including the snow that fell late lat week. The recent snow sits above 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. Yet another deep release was reported in the region on Saturday. This activity, although growing more sporadic, is keeping these layers an ongoing concern. They 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 may have developed wind slabs on several aspects in the alpine and at treeline. Forecast new snow may hide recent wind slabs.

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 and as recently as Saturday.

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.

Recognize and avoid avalanche runout zones.Cornices or smaller slab avalanches could step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 4

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