Avalanche Forecast

Issued: Apr 10th, 2017 4:19PM

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 marches on at higher elevations. Wind slabs and cornice falls are the most likely problems. Persistent layers continue to exist in the snowpack, and may become reactive during periods of strong sun or daytime heating.

Summary

Confidence

High -

Weather Forecast

Overnight: 5-8cm of new snow with light westerly winds and freezing down to 600 metres. Tuesday: Another 3-5 cm of new snow with light south winds and daytime freezing up to 1400 metres. Wednesday: A mix of sun and cloud with periods of convective flurries. Daytime freezing up to 1700 metres. Thursday: 5-8 cm of new snow with light southeast winds and daytime freezing up to 1600 metres.

Avalanche Summary

Loose dry and loose wet avalanches to size 1.0 were reported on Sunday. Saturday's reports included details of one Size 2.5 deep persistent slab triggered by a large cornice fall on a north aspect in the Valhallas. Numerous storm slabs were observed releasing naturally in various areas of the region from Size 1.5-2.5, with crown fractures ranging from 30-50 cm and north to northeast aspects seeing the majority of this activity.

Snowpack Summary

5-10 cm of new snow has added to the 30-40 cm of recent snow that blanketed upper elevations of the region late last 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.

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 - 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.

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.

Cornices or smaller slab avalanches could 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

2 - 4

Valid until: Apr 11th, 2017 2:00PM