Regions
Northwest Coastal.
Be aware of the potential for smaller avalanches to step down to deeper persistent weaknesses. The avalanche danger may be higher in the north of the region where very large, full depth avalanches remain a concern.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Clear skies are expected for Wednesday and Thursday with increased cloud forecast for Friday. Ridgetop winds should remain generally light to moderate from the east for Wednesday and Thursday, intensifying on Friday. Freezing levels should remain at valley bottom for the forecast period.
Avalanche Summary
Over the weekend, alpine and treeline features were observed running naturally to size 3.5 in the mountains northwest of Terrace. A few of these avalanches were thought to have failed on buried surface hoar. Several avalanches involving the full depth of snowpack to size 3.5 were also reported in the Ningunsaw and Bell 2 areas. One was reported being remotely triggered by a skier from a distance of 150m away. Moving forward, natural avalanche activity is expected to taper-off with forecast benign weather; however, large human-triggered persistent and deep persistent avalanches remain a concern.
Snowpack Summary
Last weekend, between 60-110 cm of new snow fell with the greatest amounts accumulating in coastal areas. Strong to extreme southwesterly winds accompanied the storm and much deeper deposits can be found in higher elevation lee terrain. At lower elevations, precipitation fell as rain and a surface (or near-surface) crust may now be found below about 1000m. Below the recent storm snow you'll likely find a couple of buried surface hoar layers from January 18th and January 23rd. These surface hoar layers continue to produce easy to hard sudden planar shears in snowpack tests, and should be approached with caution, especially in sheltered treeline terrain. The snowpack below this is generally strong and well settled. The exceptions are areas around Bear Pass and Ningunsaw where basal facets remain an ongoing concern.
Problems
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.
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.