South Columbia

Watch for signs of instability as warm temperatures arrive ahead of the storm on Monday.

Moderate - Forecast snowfall amounts are uncertain on Tuesday

Monday: Flurries bringing 10-15 cm of new snow beginning late in the day. Winds moderate from the south. Freezing level to 900 metres with a temperature inversion and alpine temperatures around -3. Tuesday: Periods of snow bringing 10-20 cm accumulations. Winds moderate from the south. Freezing level to 1300 metres with alpine temperatures around -1. Wednesday: 10-20 cm of new snow accumulating. Winds moderate to strong from the south. Freezing level to 1500 metres with alpine temperatures around 0.

Reports from Saturday show a decline in natural wind slab avalanches with a maintained potential for small, human-triggered wind slabs. Pockets of wind slab in steep lee terrain will likely remain reactive over the short term. Friday's reports included several size 1-1.5 wind slab avalanches releasing from steeper terrain on mostly north to northeast aspects. A report of particular interest details a Size 2 avalanche releasing from a lower-angle south aspect in the Valhalla Range. Although isolated, it being reported to have failed on the 25 cm-deep December 26 surface hoar layer raises concern for shallower snowpack areas. Aside from wind slab and possible persistent slab problems, additional caution is advised in steep terrain where loose snow sluffing may present an unexpected hazard.

Recent cold and clear weather has promoted both faceting of surface snow as well as the growth of surface hoar that has been reported to be up to 10mm in size in some areas. Reports also exist of a sun crust beginning to form on steep solar aspects. Below the surface, up to 30 cm of low density snow fell earlier this week. During and in the days after the storm, moderate to strong southwest and then northerly winds shifted this snow into reactive wind slabs on leeward slopes. The mid-December facet/surface hoar persistent weakness can be found buried 70-120 cm deep and is generally considered dormant. However, we are still receiving occasional reports of sudden results in snowpack tests, suggesting that it has to potential to propagate into a large avalanche if triggered, particularly in shallow spots where this layer is closer to the snow surface. The lower snowpack is well bonded and features a thick rain crust near the ground.