Regions
Kootenay Boundary.
The storm continues to build very touchy slabs above recently buried weak layers. Large avalanches are very likely to release naturally or be triggered by light additional loads.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Overnight and Tuesday: Precipitation 10-15 mm overnight becoming light in the morning as the Arctic ridge moves Southward and collides with the moist Pacific low. Temperatures trending colder as the Arctic air invades and Northeast winds build. Becoming sunny in the afternoon.Wednesday: Cold and clear.Thursday: Cold and clear.
Avalanche Summary
We suspect that storm slab avalanches are releasing naturally up to about size 2.5. If a deeper instability is triggered, expect avalanches to be in the size 3.0 range. This storm needs some time to settle and bond, forecast cold temperatures may preserve recently buried weak layers and require more time to settle and bond than when the post storm temperatures are warm. This is a complex avalanche forecasting scenario; complicated by early season timing when we have few observations coming from the field.
Snowpack Summary
The new storm slab is about 40-60 cm deep depending on where you are in the region. This storm slab has been reported to be releasing naturally during the storm, and is very touchy to light triggers like skiers/riders. Storm slabs are sitting above recently buried weak layers of surface hoar on North aspects and melt/freeze crusts on solar aspects. There are some reports of a deeply buried early season crust that formed in October. We do not know the extent of this layer with respect to aspect and areas within the region. In other regions of the interior mountains, this layer is more likely to be found in the high alpine on northerly aspects.
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.