Regions
Northwest Coastal.
Weather models are having a hard time pinning down the details of the incoming storm. Snow, wind, rain and rising temperatures are all possible, and will increase the avalanche danger.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The Jet stream clips the NW coastal region, while directing the most intense precipitation north of the area. On Thursday and overnight, 5-15 mm precipitation is expected with the freezing level climbing towards 2000 m on Thursday afternoon. Winds become strong from the south. Light snow is expected on Friday, with winds easing to moderate south-westerlies. There is a lull in the weather forecast for Friday night/ Saturday.
Avalanche Summary
A handful of size 1-2 loose wet avalanches failed yesterday on steep solar aspects. Skiers have also triggered a few small wind slabs over the last couple of days. Northeast of Bell 2, a natural avalanche at treeline was observed to have stepped down to the early January surface hoar on Sunday. While this avalanche technically occurred in the Northwest Inland region, it is a good reminder that this layer remains a concern, especially in thin snowpack areas.
Snowpack Summary
Recent strong winds have created wind slabs on a variety of slopes at alpine and treeline elevations. Some solar aspects have a thin sun crust at the surface. In some spots sheltered from the wind and sun, surface hoar has survived. Incoming snow may bond poorly to these surfaces. 40-100 cm of snow sits above a melt freeze crust buried around February 12th. This crust extends up to about 2000 m. Although the snow above is bonding well to this crust in most places, recent snow pit tests northwest of Terrace produced failures on or in facets just below this layer under moderate to hard loads. Below this, a layer of surface hoar buried late in January remains a concern in thin snowpack areas in the east and north of the region. The snowpack in these areas may also sit on a weak base of facets near the ground.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.