South Columbia

Winter is loosening its grip as sunshine and warm temperatures team up to test the snowpack in the coming days. Check out the latest Forecasters' Blog for more details: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up

Moderate - Timing or intensity of solar radiation is uncertain

Saturday: A mix of sun and cloud, clearing over the day. Light southeast winds. Freezing level rising to 1500 metres with alpine high temperatures around -4.Sunday: A mix of sun and cloud, becoming cloudier over the day. Light south winds. Freezing level rising to 1800 metres with alpine high temperatures of -2.Monday: A mix of sun and cloud. Light southeast winds. Freezing level rising to 2100 metres with alpine high temperatures of +1.

Reports from Thursday included several observations of size 1 storm slabs and wind slabs releasing with ski cutting above 1800 metres. A snowcat also managed to trigger a size 2 persistent slab that failed on the mid-January weak layer by using its blade to undercut a slope known to harbour surface hoar.A natural cycle of size 1-2.5 loose wet avalanches was reported on south-facing slopes on Wednesday. A handful of very large slab avalanches have been reported over the last couple of days: 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.