North Columbia

Watch for new wind slabs forming over old ones as the leading edge of next storm brings a first wave of new snow to the region.

Moderate - Forecast snowfall amounts are uncertain

Tuesday night: Cloudy with scattered flurries bringing a trace to 5 cm of new snow. Light to moderate northwest winds shifting southwest.Wednesday: Cloudy with increasing flurries bringing an uncertain 5-15 cm of new snow, continuing and increasing overnight. Moderate southwest winds. Alpine high temperatures around -6.Thursday: Cloudy with continuing flurries bringing an uncertain 10-30 cm of new snow, continuing overnight. Strong southwest winds. Alpine high temperatures around -3 as freezing levels rise to 1800 metres.Friday: Mainly cloudy with lingering scattered flurries as a trace to 5 cm of new snow, ending midday. Moderate west winds easing over the day. Alpine high temperatures around -9 as freezing levels return to valley bottom by end of day.

Monday's reports have shown a steep decline in storm slab activity and a transition to ski cut wind slabs. Reports from Saturday and Sunday revealed an active couple of days for avalanches in the Columbias. A more notable MIN report from Saturday describes a large (size 2) snowmobile remote (from a distance) triggered storm slab in the Clemina Creek area. (link here) Numerous other small (size 1-1.5) storm slabs were also triggered with ski cutting and skier traffic. A notable outlier was a large (size 2.5) persistent slab release that was skier triggered below ridgecrest on a southwest aspect in the Connaught Creeek area in Glacier National Park.Aside from the above report, the last reported persistent slab activity was last Sunday when a few large (size 3) persistent slab avalanches were observed on south facing alpine features. This was the final report from a widespread persistent slab avalanche cycle that was quite active last week. The failure of our recent storm to produce a renewal of persistent slab activity suggests that this layer may now be dormant.

Saturday's storm brought about 30-40 cm of new snow to the region. Winds during and since the storm drove fairly aggressive wind slab development on most aspects at higher elevations. Outside of wind loaded areas, the new snow is showing good signs of bonding well to the old snow interface, which appears for the most part to be free of any weak surface hoar crystals. Below this interface, 10 to 20 cm of older low density snow sits above old wind slabs in the alpine, and in some isolated areas above small surface hoar (feathery crystals). Avalanche activity on the 100-140 cm deep weak layer that formed during the dry spell in early December has greatly diminished over the past week. This aspect-dependant mix of facets, surface hoar, and sun crust is believed to be trending toward a dormant state after the loading test brought by Saturday's storm failed to produce consistent reports of avalanches 'stepping down'. A heavy trigger might still coax reactivity out of steep north and east facing slopes between 1900-2300 m or a steep south-facing slope in the alpine.The lower snowpack is generally strong and settled, with a crust that formed in late October near the bottom of the snowpack.