Avalanche Forecast

Issued: Apr 12th, 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.

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

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Overnight: 3-5 cm of new snow with moderate southeast winds and freezing down to 800 metres. Thursday: 5-10 cm of new snow with a chance of convective flurries providing enhanced snowfall amounts in some areas. Expect moderate southeast winds becoming southwest in the afternoon. Daytime freezing up to 1600 metres. Friday: Another 3-5 cm of new snow with light southwest winds and daytime freezing up to 1400 metres. Saturday: A few more cm of snow with overcast skies and light winds. Daytime freezing up to 1400 metres.

Avalanche Summary

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. 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

Storm Slabs

Forecast new snow and wind may develop storm slabs in the alpine and at treeline. Rain at lower elevations may result in loose wet avalanches.

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: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

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