Avalanche Forecast

Issued: Apr 5th, 2012 10:20AM

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.

ccampbell, Avalanche Canada

Sea To Sky.

Summary

Confidence

Good

Weather Forecast

Friday: Unsettled conditions with scattered flurries and sunny breaks. Freezing levels around 1000m and light winds. Saturday: A ridge of high pressure is expected to keep things mainly sunny and dry. Freezing levels are expected to hover around 1200m, and winds should remain light. Sunday: Some increasing clouds with light precipitation later in the day.

Avalanche Summary

Reports from Wednesday include natural activity up to Size 3 in response to direct sun-exposure. One natural Size 3, 160cm thick slab avalanche on a steep NE facing alpine glacier was suspected to have failed on the late-March interface. A settlement was felt 1 Km away during this avalanche, which suggests a high propensity to propagate fractures. More evidence of the widespread natural avalanche cycle during the storms earlier in the week was also observed, with slabs up to Size 3.5 running full path.

Snowpack Summary

Over 60cm of new snow in the past couple of days was redistributed by strong southwesterly winds into thick wind slabs. A predominately crusty weak interface from late March, now down 50-150cm, remains a potential failure layer for large slab avalanches, especially with heavy triggers such as cornice falls and step-down avalanches. Not only will daytime warming and sun-exposure cause surface snow to lose cohesion and cornices to weaken, they will also increase settlement rates and decrease slab stability.

Problems

Wind Slabs

Generally lurking below ridgecrests, behind terrain features, and in gullies. Sun-exposure is expected to increase sensitivity to triggers, and deeper weaknesses with step-down potential can result in very large avalanches.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 5

Cornices

Large and weak cornices could easily start popping off with sun-exposure. Not only are they a hazard in themselves, but can also act as a heavy trigger for very large avalanches on the slope below.

Aspects: North, North East, East, South East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

The potential for remote triggering, step down avalanches, and wide propagations, makes the current snowpack structure particularly tricky to manage.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Apr 6th, 2012 9:00AM