Regions
Northwest Coastal.
Confidence
Fair - Freezing levels are uncertain on Tuesday
Weather Forecast
Light flurries on Sunday are expected to become moderate snowfall overnight into Monday morning, bringing 10-15 cm to the mountains near Terrace, and 5-10 cm more inland near Smithers. Moderate south winds on Sunday night are forecast to swing to the southeast by Monday morning and then shift to southwest and build to about 35 km/hr at ridgetops by Monday afternoon. This is a relatively fast moving low pressure between two week ridges of high pressure. The next big event is forecast for Tuesday morning, when freezing levels are expected to begin to rise and heavy precipitation combined with strong southwest winds will move into the region from the Pacific. Freezing levels are expected to briefly rise as high as 1500 metres by Tuesday afternoon. Temperatures should cool and snow should continue on Wednesday.
Avalanche Summary
Reports of widespread whumpfing at treeline and above on hard windslabs. Skier accidental reported to size 2.0 from a south aspect on a convex roll in the backcountry near Shames on Saturday.
Snowpack Summary
The main concern is windslab. The old windslabs are on south through west aspects, and they are stiff and continue to be easily triggered. New windslabs are building on north through east aspects, making travel a bit tricky; limited options exist for avoiding both types of windslab. Change is coming on Monday night or Tuesday morning, when heavy snowfall and warmer temperatures may overload all of the current weakness. I have left in the paragraph from yesterday because the problems are slow to heal, and I believe they are still valid. The deep snowpack is considered to be well settled with no persistent layers of concern. There is now 30-40 cm of dry cold snow above windslabs that have developed due to strong NE outflow winds which have not bonded to the January 8th surface. These pockets of hard windslab can be triggered by light loads such as a single skier or rider. Some areas have developed surface hoar or surface facetting on sheltered slopes in the alpine and at treeline, that are now getting buried by new snow and shifting winds.
Problems
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.
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.