Regions
Northwest Coastal.
Continued stormy weather will maintain elevated avalanche danger.
Weather Forecast
Heavy snowfall or rain is expected to continue throughout the forecast period with 20-40 cm of snow (or mm of rain) each day for Friday, Saturday, and Sunday, although Friday is looking perhaps a little drier. Strong southwesterly winds are expected to ease off on Saturday and remain light to moderate on Sunday. Freezing levels around 1600 m on Friday are also expected to drop below 1500 m on Saturday, but fluctuate on Sunday.
Avalanche Summary
Very heavy loading from snow, wind, and rain has resulted in a widespread natural avalanche cycle. Reports from Wednesday include numerous wind slab and some step-down persistent slab avalanches in the Size 2-3 range, with isolated deep persistent slab avalanches up to size 3.5 from large alpine features. Below approximately 1000m numerous wet loose snow avalanches up to Size 2.5 were observed running in steep terrain. This pattern should continue throughout the forecast period.
Snowpack Summary
Heavy snowfall (with rain below approximately 1500-1000 m) and strong southwest winds have built fresh deep and dense storm and wind slabs. The slabs are likely 'upside down' with warm temperatures dropping moist dense snow on previous dry lower-density snow. A rain crust and/or surface hoar layer buried mid-December is down around a metre. Recent reports mention that this weakness has become 'electric' with recent heavy loading and has been responsible for much of the recent large avalanche activity. The November crust near the bottom of the snowpack is generally well bonded, but may 'wake up' with intense loading this week. There is potential for isolated very large and deep avalanches.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.