South Columbia

Another day of sunshine and warm temperatures should keep surface instabilities active. Concern for persistent slab problems is still on the rise.Check out the Forecasters' Blog for more: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up

Moderate -

Sunday: Sunny. Light south winds. Freezing level to 1900 metres with alpine high temperatures of -1 to 0.Monday: Sunny. Light south winds. Freezing level to 2200 metres with alpine high temperatures of +1 to +2.Tuesday: Sunny. Light to moderate southwest winds. Freezing level to 2700 metres with alpine high temperatures of +5.

Reports from Friday included numerous storm slabs and wind slabs ranging from size 1.5 to 2.5. These were triggered naturally as well as with ski cutting and all aspects and elevations were represented. Many recent loose snow avalanches were also observed in the region and in adjacent regions.On Thursday a snowcat triggered a size 2 persistent slab that failed on the mid-January weak layer when its blade undercut a slope harbouring buried surface hoar.A handful of very large slab avalanches were reported earlier last week: cornice fall triggered a size 2.5 slab on a north-west aspect at 2700 m and sun triggered a size 2.5 persistent slab on a south aspect at 2200 m. A chunk of falling glacial ice triggered a size 3.5 slab on a north-west aspect. Avalanche activity is expected to increase as we move into a period of intense sun and prolonged warming. Predictable loose wet avalanches from steep, sunny terrain should be easy to manage. The trickier problem will emerge as warmth penetrates into the snowpack to tickle deeper persistent weak layers. The next few days will be a time to avoid exposure to large sun-exposed features and keep well away from corniced slopes.

Around 20-30 cm of new snow has formed new storm slabs which overlie sun crusts on solar aspects. This latest snow sits on well-settled storm snow from regular snowfalls over the past couple of weeks. Several other sun crust layers may be found within this storm snow on solar aspects.A couple of layers buried in mid-late February (down around 70-120 cm) are variably reactive, but both have the potential to create surprisingly large avalanches if triggered. Initially, these interfaces were most reactive on solar aspects, where they present as buried sun crusts. However, persistent slabs have been triggered on shady aspects too, where surface hoar and/or facets exist.Deeper persistent weak layers from January and December are generally considered dormant, but could wake up with forecast warming, a surface avalanche stepping down, cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets. Facets linger at the base of the snowpack.