Regions
Northwest Coastal.
The storm continues, and avalanche danger is HIGH at all elevations.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Storm continuing overnight with strong southwest winds and 15-30 mm of precipitation by morning. Freezing levels will be variable across the region, likely 1200 metres in areas that receive the most precipitation in the south and around 500 metres in the north. Storm continuing on Wednesday with strong southwest winds and up to 20 mm of precipitation in the south with freezing levels around 1000 metres. Storm weakening on Thursday with moderate winds and 5-10 mm of precipitation. Clearing and cooler on Friday with light winds.
Avalanche Summary
I expect that a natural storm slab avalanche cycle is on-going in the south of the region near Terrace and also near Kitimat. The peak of the storm may have already passed through the north of the region. We have not had any reports of persistent slab avalanches, but that may be due to poor visibility and travel conditions.
Snowpack Summary
We've had a significant warming trend since the arctic outbreak, and a large storm snowfall gradient (30-40cm in the south ; 60-80cm near Stewart). The new snow fell with moderate to strong SW winds, and formed touchy soft slabs and wind slabs. Expect this new snow to bond poorly to all the windslabs (and a spotty layer of surface hoar and facets buried Jan 12th) that formed during last week's arctic outbreak conditions. The older wind slabs sit on a variable interface composed of hard wind slabs, weak surface hoar (Jan 5/6 layer) and faceted snow. If you're starting to think it's a dog's breakfast, you're right! With the recent new snow loading, the deeper slabs have remained reactive, especially on southwest facing features near ridge crests. Deeper in the snowpack, the Christmas surface hoar layer (buried 70-120 cm) is still preserved in some southern areas and has been reactive in sheltered areas and steep open features at treeline and below treeline. Lower elevations (below treeline) have moist snow below 1000m elevation, making for heavy and difficult riding.
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.
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.
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.