Regions
Kootenay Boundary.
The storm and avalanche cycle continue. Time to scale back objectives to low angle conservative terrain.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Overnight and Wednesday: Expect another fast moving storm bringing 15-20 cm of snow above 1200 metres combined with strong Southwest winds. Precipitation ending by early morning as the winds become moderate Westerly.Thursday: A small pulse of moisture may bring another 3-5 cm to Southern areas of the region. Freezing levels dropping to valley bottoms overnight and rising to about 1000 metres during the day.Friday: Broken skies with some sunny periods and moderate Northwest winds. Freezing level at valley bottoms.
Avalanche Summary
Reports of natural avalanches up to size 3.0, remotely triggered avalanches by skiers or snow machines up to size 2.5, and skier accidentally triggered avalanches up to size 2.0. Just to the North of the region, one avalanche stepped down to the ground and ran full path. Those all happened on Monday, I suspect that there was less natural activity on Tuesday but conditions are primed for human triggering with long propagations. Natural avalanche activity may increase on Wednesday with forecast new snow and wind.
Snowpack Summary
The storm slab is now between 50-100 cm deep. Below the storm snow there is about 20 cm of snow from last week that buried the late January layer of crusts and/or facets and surface hoar. This persistent weak layer from Late January continues to be the sliding layer for natural and human triggered avalanches. The mid snowpack is well settled and strong. The deeply buried weak layers of early season facets and depth hoar have been dormant, but they may become reactive with the right combination of added load and warm temperatures. The forecast new snow and wind are expected to add to the load above the late January weak layer, and may result in avalanches running naturally or increased sensitivity to human triggers at this interface.
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.