Avalanche Forecast

Moderate -

TUESDAY: Mainly cloudy. Ridge wind light gusting strong, southwest. Temperature -5. Freezing level valley bottom.WEDNESDAY: Cloudy, light flurries. Accumulation trace. Ridge wind moderate, southwest. Temperature -3. Freezing level 1200 m.THURSDAY: Snow. Accumulation 20-30 cm. Ridge wind light gusting strong, east. Temperature -2. Freezing level 1200 m.

On Saturday the east facing Mt. Corrigan slidepath produced a very large natural avalanche. The avalanche is estimated to be a size 4.0, and it took out mature timber in the path as it overran the Flathead FSR south of Corbin. Photos available here.Also on Saturday, several 20-50 cm thick storm slabs were triggered with explosives at treeline elevations. A few natural cornice falls occurred on north and east aspect, one triggering a size 2 storm slab on the slope below.Early last week, many large (size 2-3) avalanches were triggered naturally and with explosives. Most of the natural avalanches were triggered by cornices falling and releasing slabs on the December and November layers, producing 150-250 cm thick crowns.

Surface snow conditions are highly variable depending on the position of the Arctic front. The Fernie area experienced warm temperatures Saturday morning followed by a sudden drop to frigid temperatures in the afternoon. The results was a new surface crust below 1700 m. Areas closer to the divide likely stayed cold with low density snow. Higher elevations throughout the region stayed cold and windy, allowing the growth of touchy wind slabs and cornices.For the past month there has been regular avalanche activity on multiple deep weak layers. A layer buried mid-January is composed of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and a sun crust on solar aspects and is 60-80 cm deep. Another surface hoar layer from early-January is 90-110 cm deep. A widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 120-160 cm deep. Finally, a rain crust with sugary facets buried in late-November is near the base of the snowpack.The bottom line is the snowpack structure is weak. Human triggering is most likely on the shallower weak layers, but any avalanche has the potential to step down to deeper layers and become much larger.