Ongoing snowfall and wind inputs are sustaining elevated danger in the region. Persistent weaknesses deeper in the snowpack continue to be tested.
Weather Forecast
Saturday night: Flurries bringing 10-15 cm of new snow. Moderate to strong southwest winds. Sunday: Continuing flurries bringing approximately 10 cm of new snow, mainly in the afternoon. Light to moderate southwest winds. Freezing level to 1500 metres with alpine temperatures of -3. Monday: Flurries bringing approximately 10 cm of new snow, mainly in the afternoon. Rain below about 1400 metres. Light to moderate southwest winds. Freezing level to 1800 metres with alpine temperatures around 0. Tuesday: Flurries bringing approximately 10 cm of new snow to higher elevations, intensifying overnight. Rain below about 1600 metres. Moderate to strong south winds. Freezing level to 2000 metres with alpine temperatures around 0.
Avalanche Summary
Reports from Friday include extensive results of explosives control in the Whistler area, with numerous storm slabs, cornices, and wind slabs releasing from Size 1.5-2. Another highly notable report from southwest of Whistler details a remotely triggered Size 1.5 persistent slab. This avalanche released from a northeast aspect, had a crown fracture depth of about a metre, and should highlight ongoing concern for lingering weakness at our mid-February layer.Looking forward to Sunday, expect recently formed storm slabs to remain reactive to human triggers. While the bond at mid-February interface remains questionable, the possibility of large persistent slab avalanches also remains a concern.
Snowpack Summary
Stormy weather over the past week has brought 80-130 cm of recent snow to the region. Moderate to extreme southwest to southeast winds have redistributed much of this storm snow over the same time period and formed touchy new storm slabs in lee terrain at higher elevations. The combination of wind and warming temperatures has seen the storm snow settle into a slab that sits over the mid-February weak layer. This layer consists of facets and/or surface hoar overlying a thick crust. In wind loaded terrain, this layer may be down 180 cm or more. Recent observations suggest this layer is still reactive and capable of producing wide propagations if triggered. We have been in an incremental loading scenario over the past week where as this layer gradually heals, it is continually tested as new snow and wind load the snowpack. Below the crust layer, the mid and lower snowpack are well settled and strong.
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.