South Columbia

Avalanche danger will increase on sunny slopes where wet loose avalanches are very likely. Concern is increasing for persistent slabs and cornices.See the Forecaster's Blog for more: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up

Moderate - Timing or intensity of solar radiation is uncertain on Tuesday

Sunny and warm until light precipitation arrives on Wednesday. TUESDAY: Mainly sunny with some thin cloud. Light to moderate southeast winds. Freezing level to 2500 metres with alpine high temperatures of +3.WEDNESDAY: Cloudy with rain changing to flurries in the afternoon (2-5 cm possible). Light to moderate south west winds. Freezing level falling to 1700 metres late in the day, with alpine high temperatures of +1.THURSDAY: Scattered flurries (2-5cm). Light southerly winds. Freezing level around 1500 metres with alpine high temperatures around 0 degrees.

A widespread natural avalanche cycle to size 3 was reported throughout the weekend and Monday. These were primarily wet loose avalanches on sunny aspects; however, some did step down to the mid-February layer (with 50-70 cm crowns) on southerly aspects. Large cornice falls were also reported on the weekend. 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. See this MIN report for an example.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.

15-25 cm of snow from Thursday into Friday sits on sun crusts on solar aspects and well-settled storm snow on more northerly aspects. Several other sun crust layers may be found within the older storm snow on solar aspects. The main story, however, has been the sun's effect on south and west facing slopes over the past three days. Daytime heating has resulted in moist or wet snow on sunny aspects, freezing to form a crust overnight.A couple of layers buried in mid-late February (down around 60-110 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.