Avalanche Forecast

Issued: Apr 6th, 2012 4:00PM

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

pmarshall, Avalanche Canada

Sea To Sky.

Avalanche danger will rise during the day with intense spring sunshine and warming temperatures. Plan to be off big sun-exposed slopes early before the snow becomes moist or wet.

Summary

Confidence

Good

Weather Forecast

Synopsis: A ridge of high pressure should maintain mainly sunny skies on Saturday and Sunday. Freezing levels should climb to 1500m on Saturday and 1800-2000m on Sunday. Upper level winds are light and variable. An upper level low pressure system should spread more cloud and light precipitation on Monday. The freezing level should hover around 1600-1800m.

Avalanche Summary

New observations include loose-wet avalanches up to Size 2 from steep solar aspects. 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

Loose Wet

Very likely on steeper sun-exposed slopes in the afternoon. A heavy wet slide could have serious consequences if you are exposed to terrain traps.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

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

Possible

Expected Size

2 - 6

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

Valid until: Apr 7th, 2012 9:00AM