Avalanche Forecast

High -

Sunday night: Cloudy with clear periods. Light north winds.Monday: A mix of sun and cloud. Light northwest winds shifting to southwest in the evening before increasing. Alpine high temperatures around -11.Tuesday: Mainly cloudy with isolated flurries and a trace of new snow, increasing a bit overnight. Light to moderate west winds. Alpine high temperatures around -6.Wednesday: Mainly cloudy with easing flurries bringing about 5 cm of new snow, including Tuesday night's accumulations. Light northwest winds. Alpine high temperatures around -5.

Small wind slabs and storm slabs (size 1) have been reported throughout the region over the past couple of days, as light snowfall combined with strong wind to create new slabs, mainly focused in steeper lee terrain. Several larger (size 2) storm slabs were also observed in steep alpine start zones.However, given the weak nature of the snowpack, the main concern remains the possibility for triggering large deep persistent slab avalanches. Large and very large (size 2.5-3.5) avalanches have been reported regularly over the past few weeks (with the most recent report from Wednesday). Most activity in the past week was in south facing alpine terrain, but the problem has presented itself on all aspects over the past few weeks.Last weekend, a group of snowmobilers triggered a fatal avalanche near Invermere, also on the basal weak faceted grains. The avalanche was on a south aspect and ran approximately 900 to 1100 m. Two snowmobilers were fatally involved in this slide. See here for more information.

The snowpack is weak and touchy in large portions of the Purcells, with very large avalanches being reported on a regular basis. Read the Forecaster's Blog here for a more detailed description of conditions in the Purcells.5-15 cm of new snow is burying large surface hoar crystals and/or sun crusts, which could eventually develop into a touchy problem as snow accumulates. The most suspect terrain features will be steep slopes and rolls below 2000 m (where the largest surface hoar exists) and steep south-facing slopes in the alpine (where sun crusts exist).The weak nature of the snowpack lies at depth. There is a weak layer around 80 to 120 cm deep, composed of sugary faceted grains, feathery surface hoar, and a sun crust. The base of the snowpack is also composed of weak faceted grains in many parts of the region. Humans have and will continue to be able to trigger these layers in areas where the snowpack is shallow.