A solar-induced warming cycle is expected with warm temperatures this weekend.
Summary
Confidence
Poor - Timing or intensity of solar radiation is uncertain
Weather Forecast
Saturday will have prolonged periods of sunshine. Winds should remain light. Freezing level should go to around 1600 m during the day. Sunday looks bright, sunny and warm, with freezing levels going up to around 2300 m. Very little overnight cooling is expected Sunday night as clouds move in overnight. Monday will stay warm, with freezing levels around 2200 m and some good periods of sunshine.
Avalanche Summary
On Friday, a very large (up to 10 m high) cornice collapsed at 2400 m on a NE aspect in the Monashees. On Thursday, a very large avalanche (size 3) ran naturally on a south aspect all the way to valley bottom and part-way up the other side. On Wednesday, a size 3 slab failed on the mid-Feb weakness on a west aspect, with a 2 m deep crown. It was suspected that solar warming was the trigger. While avalanche activity on this layer is no longer widespread, large avalanches continue to occur on a sporadic basis. Last weekend, size 3-3.5 slabs, 100-180 cm deep, failed naturally and two size 3 avalanches were triggered accidentally by snowmobilers just south of the region near Kimberley. Solar warming may lead to another spike in deep persistent slab activity over the next few days. A number of size 1-1.5 storm slabs and wind slabs were also triggered naturally and by people over the last couple of days.
Snowpack Summary
Wind slabs in the alpine and at treeline are becoming less reactive. A melt-freeze crust exists from valley floor into the alpine on solar aspects. Older storm slabs are mainly bonding well to underlying surfaces. A key concern is a persistent weak layer of buried surface hoar from mid-February that is buried 1-2 m deep. Snowpack tests give sudden "pops" results on this layer in some areas, indicating the ongoing potential for very large avalanches. Because the layer is so deeply buried, it's unlikely to fail without a large trigger (e.g. cornice fall or explosive). However, there's always the chance of someone stumbling across a sweet spot, particularly in shallow snowpack areas.
jfloyer,
Avalanche Canada
