Regions
Kootenay Boundary.
Forecast snowfall amounts are uncertain for Tuesday night, and a touchy weak layer is being overloaded. Pay close attention to how much new snow falls in your riding area. If snowfall accumulations exceed 25cm the Avalanche Danger may be HIGH.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
The next pulse of snow is expected to roll in Tuesday afternoon with 15-25cm of snow by Wednesday morning. Winds pick up with the incoming storm and spike to strong out of the southwest Tuesday night. Freezing levels may also rise to around 1700m during height of storm Tuesday evening but generally remain below 1500m throughout the forecast period. Mostly cloudy with flurries and light to moderate southwesterly winds throughout the remainder of the forecast period.
Avalanche Summary
On Monday several skier triggered slab avalanches to size 2 were reported on northerly aspects at treeline and above. The avalanches were both wind slabs and storm slabs running on a new layer of surface hoar that was buried by the recent snow. Of note, there was a size 2 avalanche that was remotely triggered by a skier from 5m away. This means the surface hoar layer is both very sensitive to triggers and likely to propagate long distances.
Snowpack Summary
A new layer of surface hoar up to size 20mm has been buried by the recent snow and is very reactive to human triggers. This layer is down 20-40cm and is present above 1700m on all aspects except due south where it was cooked by the sun and is a crust. Sunday's snowfall amounts varied widely across the region but were generally highest around Nelson. There was significant cross loading of slopes on Sunday so expect to find touchy wind slabs on many different aspects. These storm slabs if triggered may step down to the mid February layer that is down 80-100cm resulting in potentially very large 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.
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.