Mountain Conditions

Posted on Friday, March 27, 2009

Mar 27, 2009

Whistler Avalanche conditions

For Fri Sat Sun
Alpine: Considerable Considerable Considerable
Treeline: Moderate Considerable Moderate
Below Treeline: Moderate Moderate Moderate
Avalanche Danger Rating Descriptions

Travel Advisory:
Large slab avalanches continue to be reported by ski operators across the Coast Mountains. Wind loaded soft slabs are sitting over variable surfaces in the alpine and treeline. Areas of stiff windslab are loaded onto exposed alpine features. Caution is advised around any previously shallow rocky areas that are now loaded with storm snow. Although cooling temperatures have tightened up the snowpack, we have seen widespread natural and skier triggered deep slab avalanches stepping down to the December facets. Remember that sun warming may make the snowpack more fluid and ready to react. Give cornices a wide berth as cornices have triggered many of the recent large avalanches.

Avalanche Activity:
Large slab avalanches continue to be reported throughout the Coast Mountains from steep shallow areas. These avalanches are running into skiable terrain. Widespread natural avalanche activity with dozens of deep size three slabs, and even a size four, ran last weekend. Triggers for this cycle ranged from naturals and cornice faliures to skier-remote and explosives triggered avalanches. This avalanche activity has settled down somewhat since Monday. The deeper releases were all between 1700m and 2300m on all aspects. One fracture line profile at 1775m on a NE aspect showed the bed surface to be surface hoar on a crust. Most large avalanches in the alpine appeared to involve the Dec 6 facet layer.

Wind loaded snow is sitting on a variety of surfaces in the alpine and treeline. There continue to be several persistent weak layers in the snowpack. Stepped fracture lines would indicate that the weaknesses from December, February and March are all at or near their threshold. Stability tests in profiles are indicating hard shears, but the widespread easily triggered large avalanche activity indicates a more acute weakness. As always, the areas to avoid are those where the snowpack is shallow and the weak basal layers are more extensive.