Thursday is a classic late winter day with cool temps & a few clouds. A warm storm arrives Thursday night, & then warming continues through the weekend. Peak warming may initiate a natural avalanche cycle, especially in the east where there are deeper concerns in the snowpack.
The recent winds have created wind slabs across exposed leeward and cross loaded terrain. Strong southwest wind and another shot of snow Thursday night into Friday will likely form touchy wind slabs that are expected to be problematic Friday.
The persistent slab problem appears to have been put to rest in deep snowpack areas in the west of the region, but on the eastern slopes (e.g. Kakwa/Tumbler Ridge) there have been very large recent natural avalanches. The most likely triggers are surface avalanches stepping down, cornice fall, or the weight of a machine or a person hitting a thin-spot.
A shot of cold snow Thursday night and then a pretty significant warm up this weekend.
WEDNESDAY NIGHT: Freezing level at valley bottom, light west/northwest wind, no snow expected.
THURSDAY: A few clouds, freezing level rising to about 1350 m in the afternoon, strong southwest wind, no snow expected during the day, 5 to 10 cm possible Thursday night.
FRIDAY: Broken cloud cover, freezing level climbing to about 1800 m, strong southwest wind, 5 to 10 cm of snow at upper elevations with rain at valley bottom.
SATURDAY: Scattered cloud cover, freezing level potentially climbing as high as 2000 m, strong southwest wind, no precipitation expected.
Our field team found some large and disturbingly wide avalanches in the Hasler Tuesday, lots of compelling images in their MIN report here. It's suspected that these are running on facets that are about 80 cm below the surface.
This adds to the tally of recent large avalanches they started collecting in Pine Pass on Monday. All of this activity leaves me feeling uneasy about a big warm up this weekend.
The warm temperatures last week triggered loose wet avalanches on solar (south through west) aspects. Strong winds triggered wind slabs naturally up to size 2 and explosive controlled avalanche (near Pine Pass) up to size 3.
Strong south to west winds in exposed areas have scoured some slopes and built wind slabs on others. Freezing levels reached treeline last Thursday and Friday. It has cooled since so you will likely find 5 to 10 cm of new new snow on the surface or a crust at treeline and below.
About a metre of snow covers a weak layer of facets buried mid February. Slightly deeper there is a widespread persistent weak layer from late January/early February that consists of surface hoar. It is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. These layers are both significantly shallower in the east of the region.
