Avalanche Forecast

High -

Tuesday: A mix of sun and cloud. Light southwest winds. Alpine temperatures around -15.Wednesday: Mainly cloudy with isolated flurries bringing a trace of new snow, increasing overnight. Light southwest winds. Alpine temperatures around -15.Thursday: Cloudy with scattered flurries bringing approximately 5 cm of new snow. Light to moderate southwest winds. Alpine temperatures around -11.

Sunday's reports include observations of numerous explosives-controlled persistent slab releases east of Invermere. Sizes were typically smaller, with one Size 1.5 recorded. These all occurred on north to northwest aspects in the alpine. A MIN report from the Dogtooth Range on Saturday showed remote triggered Size 1 releases occurring in sheltered areas below treeline. Another MIN report from Friday included observations of ski traffic easily producing shooting cracks in mellower terrain between 1700-2000m in the Dogtooth. These releases and cracks likely failed at the December 15th interface. Persistent slab avalanche danger can be expected to persist in areas where last week's storm snow consolidates into a slab above the December 15 interface. In areas where new snow has not yet consolidated into a slab, expect continued potential for triggering loose dry avalanches in steep terrain.

Last week's storm brought 30-50cm of new snow to the region. Shifting winds (most recently from the northwest) have redistributed this storm snow into wind slabs on a variety of aspects at higher elevations while cold temperatures have inhibited slab formation elsewhere. The storm snow lies over a wide variety of old surfaces, including large surface hoar (weak, feather-like crystals), hard crusts formed by sun or wind, and sugary facets. The bond at this old snow interface is of critical importance where the overlying storm snow has consolidated into a slab. The most concerning areas are those that saw pronounced surface hoar development before the storm, particularly in sheltered areas at and below treeline. Recent snowpack tests show wide ranging reactivity at this interface but suggest that it may be most reactive on northerly aspects. A crust which was formed by rain in late November remains a major feature in the snowpack and is down approximately 60-100cm at tree line elevations. This interface shows good signs of bonding in the Purcells, but has indicated some reactivity in steep, variably loaded features in adjacent regions.