Avalanche Forecast

Issued: Jan 23rd, 2017 3:48PM

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

Avalanche Canada shorton, Avalanche Canada

Conditions are improving, but the consequence of triggering a large persistent slab avalanche warrants a cautious approach to steep open terrain.

Summary

Confidence

High - Due to the number and quality of field observations

Weather Forecast

TUESDAY: Cloudy with isolated flurries along the coast, 20-40 km/h southwest winds, freezing level up to 500 m.WEDNESDAY: Flurries with up to 5 cm of new snow, 30-50 km/h southwest winds, freezing level up to 700 m.THURSDAY: Flurries with 5-10 cm of new snow, 50-70 km/h southwest winds, freezing level up to 800 m.

Avalanche Summary

Over the weekend there were several reports of natural and skier triggered wind slabs in the size 1-1.5 range, primarily on west aspects. Evidence of a previous widespread natural avalanche cycle during last week's storm was also reported, where size 2 to 3 avalanches released in both the storm snow as well as on deeper surface hoar layers (likely the January 5th). Triggering wind slabs as well as lingering persistent slabs remains a possibility at higher elevations.

Snowpack Summary

Light flurries and moderate winds have formed fresh wind slabs above 40-60 cm of settled storm snow from last week. Freezing levels reached 1200 m during the storm, which has left a hard supportive crust at lower elevations. At this point there is some uncertainty as to how deeper persistent weak layers are responding to the recent loading and warming. Several weak surface hoar and facet interfaces were reactive during the storm, but have shown signs gaining strength since. This includes the January 5th layer about 50 cm deep and the December 25th layer up to a metre deep. These are not typical conditions for this coastal region, and it will take more time to gain confidence about the distribution and likelihood of triggering these deeply buried weak layers.

Problems

Wind Slabs

An icon showing Wind Slabs
Lingering wind slabs are expected to remain reactive to human triggering in steep wind loaded terrain features.
Use ridges or ribs to avoid pockets of wind loaded snow.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Use caution on open slopes and convex rolls

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
It may still be possible to trigger avalanches on buried weak layers (Dec 25, Jan 5th, Jan 12th surface hoar) ...or have a smaller avalanche 'step down' and trigger one of these layers.
Assess start zones carefully and use safe travel techniques.Carefully evaluate terrain features by digging and testing on adjacent, safe slopes. Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Jan 24th, 2017 2:00PM