Forecast snowfall for the storm varies across the region, and it's not a clear split between north and south. Avalanche danger will increase over the day as new snow accumulates. Expect warming to bring wet loose avalanche concerns into the mix later in the day.
Forecast snowfall for the storm varies across the region, and it's not a clear cut split between north and south. In areas where less than 15 cm of new snow accumulates, anticipate fresh wind slabs to form in leeward terrain. In areas that see more, a more widespread storm slab problem may emerge by the end of the day.
Warming temperatures and possible rain will promote wet loose avalanche activity at lower elevations on Sunday. These are most likely to occur on steep slopes and may initiate naturally or with a human trigger. The warmest temperatures are expected in the south of the region.
Two layers that cause concern in the northern part of the region include:
Loading from new snow and avalanches in surface snow layers may test these layers over the weekend.
Saturday night: Cloudy with Continuing flurries bringing 5-10 cm of new snow. Moderate to strong southwest winds.
Sunday: Cloudy with easing flurries bringing a trace to 10 cm of new snow, ending with light rain below 1500-1700 metres. Moderate to strong southwest winds easing over the day. Alpine temperatures reaching 0 as freezing levels rise to 1800-2000 metres, warmest in the south of the region.
Monday: Mainly cloudy with isolated flurries in the north of the region. Moderate south winds easing over the day. Alpine high temperatures around -2 in the north of the region, closer to 0 in the south.
Tuesday: Cloudy with flurries and a trace to 5 cm of new snow. Light to moderate south winds. Alpine high temperatures around -4.
A report from Thursday in the McGillivray pass area in the north of the region included observations of several storm slabs reaching size 2.5 (large) releasing naturally from steep north aspects in the alpine during a period of intense snowfall.
Last Saturday, a few explosives-triggered avalanches in the north of the region stepped down to the Christmas surface hoar layer mentioned in our snowpack summary, buried 50-60 cm deep at the time.
Two Thursdays ago, explosive control work produced a size 2 avalanche off the Duffey Lake road that released on the mid November facet/crust layer.
2-day snow totals over the region are expected to reach a variable 10-30 cm by the end of the day on Sunday. The new snow is burying recent wind slabs and wind-affected surfaces in exposed areas at all elevations and soft, low density snow in sheltered areas.
90-150 cm of snow currently sits above a weak layer of surface hoar from Christmas that professionals are tracking in the north of the region. It may be found at treeline and below on shaded aspects in sheltered areas.
A deep persistent weak layer remains a serious concern at the bottom of the snowpack in the northern half of the region (e.g., Duffey, Hurley). It's made up of sugary faceted grains and a hard melt-freeze crust. This layer is most likely to be triggered in thin, rocky features where it exists closer to triggering forces on the surface.
Concern for very large avalanches releasing over this weak basal layer will increase in areas of the north where loading from new snow, wind, and rising temperatures strain the snowpack and cause avalanche activity in surface layers.
There are currently no concerns about deep weaknesses in the snowpack near Coquihalla summit and elsewhere in the south of the region.
