Significant amounts of new snow and warming will set up very dangerous avalanche conditions.
Weather Forecast
Heavy precipitation is expected to start on Friday afternoon. The freezing level is expected to remain at valley bottom in this region, although temperatures will climb to around -5C. Overnight, accumulations will be heavy and strong southwesterly winds will blow. Around 20-30 cm dense new snow is expected to be on the ground by Saturday morning. On Saturday, further heavy snowfall is anticipated, as unstable, convective air moves in behind the storm. Temperatures will cool slightly and strong SW winds will continue to blow. On Sunday, another punchy winter storm system will bring further heavy snowfall.
Avalanche Summary
Only loose snow activity was observed on Thursday. I anticipate a significant avalanche cycle will occur with heavy amounts of dense new snow expected to fall on existing cold, low density snow.
Snowpack Summary
30-80 cm very low density snow has accumulated over the last few days. The Coquihalla and areas around Hope have seen the highest amounts. Winds recently picked up into moderate range from the southwest - just enough to create some soft slabs on lee slopes in exposed areas. Below the storm snow lies a rain crust at lower elevations (up to around 1800 m) and old wind slabs in exposed areas at higher elevations. Weak layers lower in the snowpack have generally ceased to be of concern, except perhaps in thin rocky areas.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.