While the avalanche hazard is slowly dropping, human triggering remains possible. The primary concern is the threat of superficial slabs stepping down to the deep persistent weakness which could result in full-depth avalanches.
Moderate to strong S and SW winds have built wind slabs in lee features in the alpine and down into treeline. Wind-loading is expected to continue through Wednesday. These slabs are a particular concern where they sit over weak facets which could result in step-downs to the basal layers.
Weak facets and depth hoar associated with crusts near the base of the snowpack continue to produce slab avalanches 60-100 cm deep. Any area with a stiffer slab over facetted lower packs has the potential to generate a larger avalanche that steps down ground.
Ski hill reported continued wind slab and cornice development. Explosive control triggered wind slabs up to size one. Sunshine reported one deep persistent explosive triggered avalanche in Delirium.
On Monday a large cornice failure on Ptarmigan Peak (SE aspect) triggered a 250 m wide windslab that scoured down into the basal facets. (See photo)
A skier triggered deep-persistent avalanche was reported from a shallow west facing aspect above Sherbrook Lake on Monday.
15-20 cm of storm snow from the past week, combined with strong W/SW winds, has formed wind slabs in alpine lee areas which extend down into treeline.
The mid and lower snowpack is faceted and weak, with facet/crust interfaces near the ground. This is more pronounced east of the divide, while western regions display a deeper more settled snowpack.
Snowpack depths at tree-line are about 60 cm in eastern areas and 100 cm west of the divide.
The forecast is for a mix of sun and cloud on Christmas Day followed by light flurries along the Continental Divide on Boxing Day. Ridgetop winds will be from the west/southwest in the moderate range with stronger gusts. Day-time high temperatures at treeline forecasted to be around -8.
