Avalanche Forecast

Issued: Apr 8th, 2017 4:19PM

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

cgarritty, Avalanche Canada

North Columbia.

The upper snowpack will gain strength overnight, but watch for breaks in cloud cover to undermine slab and cornice stability on Sunday. Spring sunshine packs a punch.

Summary

Confidence

High -

Weather Forecast

Sunday: Mainly cloudy with isolated flurries and a trace of new snow. LIght west winds. Freezing level to 1700 metres with alpine temperatures of -4.Monday: A mix of sun and cloud. Light southwest winds. Freezing level to 1700 metres with alpine temperatures of -5.Tuesday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1600 metres with alpine temperatures of -5.

Avalanche Summary

Reports from Friday showed storm slabs releasing naturally from Size 2-2.5 on north aspects in the Rogers Pass area. Smaller wind slabs (Size 1-1.5) released naturally and with ski cutting on west aspects northeast of Revelstoke. Numerous loose wet releases up to Size 2 occurred over the previous 24 hours.Reports from Thursday included observations of two storm slab releases, Sizes 1 and 2.5. The smaller of these was skier triggered and the larger ran naturally. They both occurred on north aspects at 2200 metres and above. Loose wet avalanches were observed running naturally and with ski cutting from Size 1-2.5 in various areas in the region.Reports from Wednesday included details of one natural Size 3.5 deep persistent slab release that occurred on a northeast aspect in the alpine, just northeast of Revelstoke. It was triggered by a smaller storm slab that released above it due to solar warming. Natural cornice falls up to size 3.5 were reported on Tuesday.

Snowpack Summary

Roughly 30-40 cm of new snow has formed fresh storm slabs on the surface after a series of storms over the end of the week. These new storm slabs have developed above a mix of old surfaces that include melt-freeze crusts at treeline and below and on solar aspects in the alpine. In addition to storm slab formation, the new snow has also contributed to fragile new cornice growth. 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 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 a concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.

Problems

Storm Slabs

New snow and variable winds have developed storm slabs and wind slabs at higher elevations. These slabs may remain reactive to human triggering on Sunday and are more likely to react in areas that were exposed to recent strong winds.

Be especially careful with wind loaded pockets near ridge crests and roll-overs.Use ridges or ribs to avoid pockets of wind loaded snow.Be increasingly cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 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 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 9th, 2017 2:00PM