Avalanche Forecast

Issued: Apr 6th, 2014 9:59AM

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

South Coast.

What's going to happen to the snowpack if it warms up significantly on Monday/Tuesday? 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. Precipitation will be less on the Duffy.Monday: A mix of rain and snow up to 10 mm. Freezing levels rising to 2300 m. Alpine temperatures near 5.0 degrees. Ridgetop winds moderate from the SW, gusting strong. Freezing levels will slowly start to drop overnight to 1800 m. Tuesday: Periods of rain 15-25 mm. Alpine temperatures near 5.0 and freezing levels rising to 2100 m with no re-freeze overnight. Ridgetop winds remain strong from the SW.Wednesday: A mix of sun and cloud. Light precipitation. Alpine temperatures near -3.0 and freezing levels dropping to 1200 m. Ridgetop winds moderate from the SW.

Avalanche Summary

Small loose dry avalanches were seen from steep rocky terrain features. Loose wet avalanches were also seen on solar aspects. I suspect natural activity will continue with the warmer temperatures and rain through Monday/Tuesday. Smaller surface avalanches may trigger deeper weak layers, especially in thinner snowpack areas.

Snowpack Summary

Up to 20 cm of new snow sits above a mix of surface hoar, facets and melt freeze crusts. The new snow seems to have a poor bond to old surfaces and isolated wind slabs likely exist. Warmer temperatures and rising freezing levels will likely weaken the snow surfaces and become moist or wet.Recent warm temperatures have helped to settle and strengthen the upper snowpack and snowpack tests have been producing hard resistant planar shears on the late March crust down 30-50 cm.The persistent weak layers from early March and early February continue to be a concern. The March melt-freeze crust/surface hoar is reported to be down 60 - 100cm. The February crust/facet/surface hoar layer is now deeply buried down 150 - 250cm. These layers are mostly inactive at this time, but could re-awaken with extended warming, solar influence and precipitation through the forecast period.

Problems

Storm Slabs

New snow with strong SW winds has set up storm and wind slab problems on steep lee terrain features. Watch for sensitive storm slabs lee of both ridge crest and mid slope features like ribs/rock outcroppings. Cornices may become weak 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

With warmer temperatures, limited overnight re-freeze and rain forecast, loose wet avalanches are likely. A good indicator of weak snow is wet or moist surface snow, snowballing, and natural avalanches.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Avoid slopes when temperatures rise and the surface snow becomes moist or wet and shows signs of instability, like pinwheels and natural avalanches. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

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