Avalanche Forecast

Issued: Apr 6th, 2014 10:01AM

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

swerner, Avalanche Canada

Sea To Sky.

What's going to happen to the snowpack if it warms up significantly over the next couple of days? Read a discussion here...

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

By Tuesday the cold front will reach the south coast bringing light-moderate precipitation, cloudy skies and rising freezing levels.Monday: A mix of rain and snow with freezing levels rising to 2100 m. Alpine temperatures near 2.0 degrees. Ridgetop winds moderate from the SW, gusting strong. Freezing levels will slowly start to drop overnight to 1600 m. Tuesday: Periods of snow 15-25 cm. Alpine temperatures near 0.0 and freezing levels rising to 1700 m with no re-freeze overnight. Up to 20 mm expected by Tuesday. Alpine temperatures near 2.0 degrees. Ridgetop winds remain strong from the SW.Wednesday: Snow 5-10 cm. Alpine temperatures near -3.0. Ridgetop winds light from the SW.

Avalanche Summary

On Friday, a deep persistent slab avalanche occurred on a NE aspect at 2400 m. It is suspect that it failed on the mid-March interface. Additionally, numerous size 1 wind slab avalanches were easily triggered by the weight of a person on leeward loaded slopes near ridgetop. A natural cornice failure also pulled out small size 1 wind slab from the slope directly below.

Snowpack Summary

Higher elevation areas have recently received up to 20 cm of new snow which sits on a variety of old snow surfaces including surface hoar, facets and melt freeze crusts. Isolated wind slabs have formed and a poor bond seem to exist, especially on slopes with a buried crust.Recent warm temperatures have helped to settle and strengthen the upper snowpack and tests are producing hard resistant planar shears on the late March crust. Below treeline a spring-like melt-freeze snowpack exists. Persistent weak layers exist lower in the snowpack. The mid-March surface hoar/ crust interface now down 80 -110 cm and is decreasing in sensitivity to triggering. The early-March crust/facet layer is down about 100-150 cm and the early February layer is now down close to 200 cm. These layers are largely dormant at this time; however, they should remain on your radar as we begin to transition into a warm-up with minimal overnight refreeze through the forecast period.

Problems

Storm Slabs

New snow and wind will add to the storm and wind slab problems. A poor bond may exist, especially on slopes with a buried crust. Natural avalanche activity is possible for tomorrow and rider triggers are likely. Cornices are a concern with warming.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>Give cornices a wide berth when travelling on or below ridges.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Deep Persistent Slabs

Three buried weak layers exist in the snowpack. Deep releases have become rare, but I would be concerned about an increased likelihood of a large destructive event during a period of intense warming.

Be aware of the potential for large, deep avalanches due to the presence of buried facets and surface hoar.>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Loose Wet

Rising freezing levels and warm temperatures for the next 36 hrs will likely make the upper snowpack weak and cohesionless. A good indicator of weak snow is snowballing, wet or moist surface snow and natural avalanche activity.

Watch for clues, like pinwheels from slopes, moist and/ or wet snow surfaces means that the snowpack is warming up and becoming weak. >Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Apr 7th, 2014 2:00PM