South Columbia

Sunday is set to be great day to be in the mountains, with lots of new snow and weather clearing. Manage the inevitable euphoria with a constant reminder that the new snow needs time to settle and that storm slabs are primed for human triggering.

High -

Saturday night: Cloudy with diminishing flurries bringing another 5-7 cm of new snow. Moderate to strong northwest winds easing to light by morning.Sunday: A mix of sun and cloud, becoming sunnier over the day. Light north winds. Alpine high temperatures around -11.Monday: A mix of sun and cloud. Light west winds. Alpine high temperatures around -12.Tuesday: Mainly cloudy. Light southwest winds. Alpine high temperatures warming to -5 as an alpine temperature inversion layer establishes toward evening.

Preliminary reports from Saturday show evidence of a natural cycle of small storm slab avalanches focused in steep, unsupported terrain. Small storm slabs (size 1 or less) were also reactive to skier triggering throughout the day.Reports from before the storm showed a steady declining trend in persistent slab avalanche activity. On Wednesday, reported activity was limited to two events. One was a large (size 2) persistent slab avalanche that was triggered by a skier in the far southwest of the region as they entered an open glade below a treed ridge on a southeast aspect at 2200 metres. The second was a small wind slab on a west facing aspect at ridgecrest.  Looking forward, expect diminishing snowfall and wind to decrease natural avalanche activity while the potential for human triggering remains elevated. Although the likelihood of storm slabs 'stepping down' to deeper persistent slab problems is in question, travel plans should account for very large avalanches as the possible result.

Saturday's storm left about 20-30 cm of new snow on the surface. Below the new snow, 10 to 20 cm of older low density snow sits above old wind slabs in the alpine, and in some isolated areas above small surface hoar (feathery crystals).A weak layer that formed during the dry spell in early December is now 70 to 130 cm deep. The layer is composed of facets, surface hoar, and a sun crust on steep south-facing slopes. Although activity at this layer has greatly diminished over the last week, it remains a concern for the possibility of surface slabs acting as a trigger for 'step down' avalanches. The places of greatest concern for this type of avalanche will be north and east facing slopes between 1900-2300 m and steep south-facing slopes in the alpine.The lower snowpack is generally strong and settled, with a crust that formed in late October near the bottom of the snowpack.