North Columbia

Cold temperatures will keep persistent slab problems in play for longer than usual. Be especially wary of wind-affected snow at lower elevations.

High -

Wednesday: Mainly cloudy with isolated flurries and a trace of new snow. Light west winds. Alpine high temperatures of -17.Thursday: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Light west winds. Alpine high temperatures of -17.Friday: Cloudy scattered flurries bringing 2-5 cm of new snow, increasing overnight. Light east winds. Alpine high temperatures of -15.

Recent reports show continued observations of wind slabs releasing to Size 1 with skier traffic and ski cutting, primarily on south aspects around exposed terrain features in the alpine. One naturally triggered Size 1.5 was also observed on Sunday. Skier traffic has also been producing small dry loose sluffs from steep, sheltered terrain. Persistent slab avalanche danger remains a primary concern in areas where last week's storm snow consolidates into a slab above the December 15 interface. In areas where the storm snow has not yet consolidated into a slab, expect continued potential for triggering loose dry avalanches in steep terrain.

Last week's storm brought 40-60cm of new snow to the region. Shifting winds (predominantly from the north) have since redistributed this storm snow into wind slabs on a variety of aspects at higher elevations while cold temperatures have inhibited slab formation elsewhere. Cold has also worked to decrease the cohesion and reactivity of older wind slabs. 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 in areas where the overlying snow has consolidated into a slab. The most concerning areas are those that saw pronounced surface hoar development before the storm, such as sheltered openings 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 is another major feature in the snowpack and is down approximately 80-110cm at treeline elevations. Recent evidence suggests it may be coaxed into reacting in steep, variably loaded terrain features in the alpine.