Continued snowfall with consistently strong southwesterly winds will gradually increase avalanche danger over the next few days. If 24 hour new snow amounts exceed 20 cm, increase the danger to high for exposed treeline and alpine areas.
70-100 cm of recent snow is available to build wind slabs on mainly north through easterly aspects in response to strong southwesterly winds. Especially east of Terrace, a chance of step-down to lower layers exists, increasing the potential size for that part of the region.
The rain on snow event will likely result in loose wet avalanches below treeline.
Precipitation amounts given are for Shames area. Heavier precipitation expected for Friday and Saturday near coastal inlets.
Thursday night: 5-10 cm new snow. Strong southwesterly winds. Freezing level around 1200 m.
Friday: 5-10 cm new snow. Strong southwesterly winds. Freezing level around 1200 m.
Saturday: 10-20 cm new snow. Strong southwesterly winds. Freezing level around 1000 m.
Sunday: 5-10 cm new snow. Moderate southwesterly winds. Freezing level around 800 m.
On Wednesday, natural and explosive triggered size 2 storm slab avalanches were reported throughout the south of the region. Some of these natural events may have run during the widespread natural cycle that occurred during the big storm last weekend.
Reports of deep persistent slab avalanches have been trickling in throughout the month, with the last reported event occurring on Jan 17th. They are associated with a November crust layer near the base of the snowpack which has produced very large avalanches (size 3+) with crown depths of around 2 m. These have typically run in alpine terrain, on lee or cross-loaded slopes. Recent loading has been a good test for this layer and it seems to be trending less reactive.
70-100 cm or recent storm snow is settling rapidly with mild weather. In exposed areas, expect southerly winds to build fresh wind slabs on north aspect slopes. The new snow rests on extensively wind affected surfaces at upper elevations, and a thick layer of weak facets in sheltered areas treeline and below.
A deep crust from mid November lurks at the base of the snowpack. Although the last reported avalanche on this layer was from Jan 17th, I wouldn't write this layer off. At this time it is most likely to react in response to a large trigger such as a cornice fall, or in response to significant warming.
