Natural avalanches are expected on Tuesday with reactive slabs at higher elevations and loose wet avalanches below. The snow will load buried weak layers and could produce very large slab avalanches.
A couple of problematic layers may be found around 80 to 180 cm deep. The layers are primarily in the north of the region (e.g. Duffey, Hurley) and include weak layers of surface hoar and faceted grains above a hard melt-freeze crust. The likelihood of triggering a persistent slab has reduced, but the consequence of doing so remains high.
New storm slabs will continue to build Monday night and Tuesday. The new snow/ rain load will destabilize the snowpack and natural avalanches are likely. New wind slabs are expected to form at higher elevations due to strong southerly wind.
Yet another strong Pacific frontal system is slated to hit the Coastal regions tonight and persist until Wednesday morning bringing rising freezing levels, heavy precipitation, and strong to extreme wind. There will likely be a division in this region with the Coquihalla seeing heavier precip, while the Duffy sees a bit less as it falls as snow. Regardless, Tuesday will see significant weather.
Monday Night: Snow 5-10 cm (up to 20 mm on the Coquihalla) with freezing levels near 1300 m. Alpine temperatures near -2 and ridgetop wind strong from the south- southeast.
Tuesday: Snow 10-25 cm (30-45 mm on the Coquihalla) with freezing levels rising to 2000 m. Alpine temperatures near 0 degrees with strong to extreme ridgetop wind from the southwest.
Wednesday: Generally a drying and cooling trend bringing a mix of sun and cloud. Alpine temperatures near -4 and light southwesterly wind. Freezing levels near 900 m.
On Monday, no new avalanches were reported at the time of publishing this forecast.
Two large avalanches were observed near Duffey Lake on Saturday, described here and here. It is suspected that both avalanches were triggered naturally and on the weak layers described in the snowpack summary. Also, a notable skier-triggered avalanche occurred near Whistler, not far from this region (see the Sea to Sky bulletin for more info).
New and reactive storm and wind slabs will continue to build Tuesday. The storm is expected to drop around 15 cm Monday night and another 20-30 cm Tuesday. The storm will come with strong southwest wind so wind slabs are expected at higher elevations. Treeline and below treeline elevations may see a loose wet avalanche cycle where the precipitation falls as rain. In sheltered areas, this snow may overlie surface hoar. The higher snow amounts mentioned above are forecast for the Coquihalla with less expected in the North (Duffy, Hurley).
A melt-freeze crust from early December is found around 80 to 180 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. This persistent weak layer is most prevalent in the north (e.g., Duffey Lake, Hurley).
