We're looking at a sunny & warm weekend which will destabilize the snowpack throughout the region. Cornice failures and loose wet avalanches are expected to be widespread, and there is potential for larger avalanches to fail naturally during periods of peak warming.
Cornice failure is likely this weekend as the strong mid-March sun and warming temperatures go to work. As cornices impact underlying slopes there is potential for them to trigger persistent slab avalanches.
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 rising freezing level this weekend may wake this problem up. The most likely triggers are surface avalanches stepping down, cornice fall, or the weight of a machine or a person hitting a thin-spot.
Potentially large loose wet avalanches are likely Saturday afternoon, especially on steep solar aspects.
It looks like this will be the weekend where the weather really transitions from winter to spring.
FRIDAY NIGHT: Freezing level holding around 1500 m, strong southwest wind, trace of snow in most locations but Mackenzie and the Pine Pass could see 10 to 15 cm of snow at upper elevations with rain at valley bottom.
SATURDAY: Scattered cloud cover, freezing level climbing to about 2100 m, strong southwest wind, no significant precipitation expected. Very little overnight refreeze expected Saturday night.
SUNDAY: Scattered cloud cover, freezing level holding between 2000 and 2500 m, strong southwest wind, no significant precipitation expected. Freezing level returning to valley bottom Sunday night.
MONDAY: A few clouds, freezing level rising to 2000 m, moderate southwest wind, no significant precipitation expected.
The rising freezing level this weekend may induce a natural avalanche cycle as the snow is destabilized by warming temperatures. Some natural cornice failure was noted on Thursday which is likely a portent of things to come. 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 dramatic rise in temperature this weekend is going to be a good test for our snowpack. Wind effect is widespread in the alpine and treeline across the region and solar aspects currently sport a sun crust. The north of the region around Pine Pass picked up almost 15 cm of new snow Thursday night, but very little new snow has fallen recently in the rest of the region.
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.
