The storm is easing off, but avalanche hazard will remain heightened for now. Conservative terrain selection is recommended.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
TUESDAY NIGHT - Cloudy with isolated flurries, up to 5 cm / light to moderate southwest winds / freezing level 1300-1400mWEDNESDAY - Mainly cloudy with isolated flurries, up to 5 cm / light to moderate southwest winds / freezing level 1400mTHURSDAY - Cloudy with scattered flurries, up to 5 cm / light southwest winds / freezing level 1300mFRIDAY - Cloudy with sunny periods and isolated flurries / freezing level 700-1000m
Avalanche Summary
There have been recent reports of size 1 rider triggered storm slab avalanches at treeline. On Saturday, November 24 a human triggered size 3 avalanche was reported in the region. This avalanche likely ran on the October crust, as it was reported as a full depth avalanche. Two reports on this avalanche can be found on the Mountain Information Network.
Snowpack Summary
The storm that arrived Sunday night has continued to deliver snow over the South Columbia region, bringing total accumulations to anywhere from 40-75 cm by Wednesday morning. This snow sits on top of a weak layer of surface hoar (feathery crystals) and sun crust on steep south facing slopes. The surface hoar is widespread at treeline and below, but it may be found in sheltered alpine areas. At the base of the snowpack is a crust that formed near the end of October. This crust has shown limited reactivity in the South Columbia region, but with recent additional snow, high winds and warm temperatures, this layer could come into play. Snowpack depths taper quickly with elevation, many areas have over 200 cm in the alpine, between 100-160 cm at treeline, and 10-100 cm below treeline.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.