South Columbia

Direct sun is likely to weaken surface snow layers and give cornices a bit of an extra nudge. Avalanche danger may spike higher than forecast on sun-exposed slopes.

Moderate - Forecast snowfall amounts are uncertain on Thursday

THURSDAY NIGHT: 10-20 cm overnight with moderate south-westerly winds.FRIDAY: Cloud clearing. Treeline temperature near -8. Light winds.SATURDAY: Sunny. Treeline temperature near -3. Light winds.SUNDAY: Mainly sunny. Treeline temperature near -1. Light winds. 

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 beast will be when warmth penetrates into the snowpack and starts tickling deeper persistent weak layers. I'd avoid exposure to large sun-exposed features and keep well away from corniced slopes over the next few days.

Around 20 cm new snow has formed storm slabs and variable wind slabs, which overlie sun crusts on solar aspects. A couple of layers buried in mid-late February (down around 60-120 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.