North Columbia

Touchy storm slabs sit above several deeply buried weak layers, which are reactive to human triggers and propagating far.  Be disciplined: perform cautious route-finding and limit overhead exposure.

Moderate - Timing, track, or intensity of incoming weather system is uncertain

TUESDAY: Mostly cloudy, light to moderate northwesterly winds, alpine temperature near -12 C, freezing level below valley bottom.WEDNESDAY: Cloudy with snowfall, accumulation 15 to 25 cm, moderate westerly winds, alpine temperature near -4 C, freezing level near 1200 m.THURSDAY: Cloudy with snowfall early morning, accumulation 15 to 25 cm, moderate westerly winds, alpine temperature near -8 C, freezing level near 1200 m dropping to below valley bottom.

On Sunday, numerous slab avalanches were reported in the region.  Storm and wind slabs were small to large (size 1.5 to 3) at all elevations and aspects and triggered naturally and by skiers.  Many persistent slab avalanches were reported on all of the layers described in the section below.  They were generally large (up to size 3), on all aspects, between 1500 and 2600 m, and triggered naturally and by large loads.  One avalanche occurred on the November crust/facet layer, on a slope that was heavily skied, with over 300 skiers on it this season.  Similar avalanches were reported on Saturday, showing a steady trend of avalanche activity.Looking forward, dangerous snowpack conditions will persist in the region until a more stable weather pattern governs and we see a decrease in avalanche observations. All of our buried weak layers (described below) continue to produce large, destructive avalanches from natural and human triggers. Recent storm slabs and wind slabs have the potential to step down to deeper weak layers, which could produce large, destructive avalanches.

Around 100-200 cm of storm snow from the past two weeks has formed a widespread storm slab and wind slabs in lee features, which sit over an unstable snowpack.  There are four active weak layers that we are monitoring:1) 80 to 150 cm of snow sits on the crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, except for possibly high elevation north aspects. The surface hoar is 5 to 20 mm in size and was reported up to tree line elevations and possibly higher.2) The early-January persistent weak layer is 120 to 170 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands.3) Another weak layer buried mid-December consists of a facet/surface hoar/crust combination, which is buried 200 cm or more below the surface. It is most problematic at and below tree line.4) A crust/facet layer from late November is yet another failure plane responsible for recent very large avalanches.