Backcountry Advisory 

As of Wednesday, May 16

The early part of the week brought us 15-20cm of new snow in the alpine terrain. The snowline was at times down to the 1,300 metre elevation. Moderate winds from the SE. and SW. have resulted in variable distribution of the new snow layers. On Wednesday morning, pockets of soft slabs of up to 40cm in depth were observed on some isolated lee slopes.

At this time of year, daily temperature fluctuations cause any new snow to settle out rapidly. It may initially fall as light density winter-like snow, but daytime warming and moisture absorbed from the underlying moist layers will generally quickly change its quality. If the snow becomes too moist however, it will lose stability and begin to sluff or snowball naturally. If the underlying old snow surface is a smooth crust, even an initially small sluff has the potential to amass into a considerable river of destructive mush.

A cornice fall earlier this week triggered a deep slab release down to the November facet layer on a steep rocky N. aspect. Keep it in mind as a possibility whenever a series of warm days and nights destroys the crusts that are maintaining the stability of the snowpack. The deeper slab releases are more likely to occur in rocky terrain where the snow cover remained relatively shallow throughout the winter. In these areas, the facetted layer developed more extensively, and the warm temperatures will permeate down to the weak layer more quickly.

Moist snow layers will generally stabilize when cooling occurs. Cornices on the other hand may become more brittle when a period of warm weather has caused them to soften and droop and is then followed by a quick drop in the temperature. Stay well away from the edge if you are travelling the ridgelines. Allow for a large margin of error – a cornice failure could pull back into the old layers. Many accidents are the result of larger then expected cornice releases.

Travel with caution if you are heading into the mountains. Get as much snow and weather information as possible before you leave, but remember that Mother Nature will always prevail. Don’t be too stubborn to turn back if conditions are beginning to compromise the safety of your group.

As of May 16, the avalanche danger is rated as MODERATE. This may increase during the day with exposure to the sun or warming temperatures.

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