Regions
Kootenay Boundary.
Confidence
Fair - Intensity of incoming weather is uncertain on Sunday
Weather Forecast
Saturday: light to moderate snowfall / moderate northwest winds increasing in the evening / freezing level at 800mSunday: moderate snowfall / moderate to strong southwest winds / freezing level rising to 1300mMonday: light snowfall / light to moderate westerly winds / freezing level at 1100m
Avalanche Summary
A size 2 natural fresh windlsab avalanche was reported in the Nelson area on thursday. It ran 200m and occurred on a north aspect at treeline. Explosives control in the area also produced numerous size 1-1.5 avalanches with crowns ranging from10-60cm.
Snowpack Summary
Significant snowfall and strong to extreme winds earlier in the week created extensive windslabs in the region. In some parts of the region this windslab is sitting on a freezing rain crust that developed on Tuesday morning. Although it's reasonable to think that these windslabs have started to strengthen somewhat, the combination of more recent light snowfall and moderate winds have continued to create fresher windslabs at ridge top. It should also be said that snowfall accumulations over the past few days have been quite variable throughout the region with with 24hr snowfall amounts on Thursday morning ranging from 2cm to 29cm. Reactivity on the aforementioned crust (which sits about 25cm below the surface in wind-neutral areas) may develop with increased load forecast for Sunday. Layers of concern deeper in the snowpack include a surface hoar/facet layer from mid-December and weak basal facets at the base of the snowpack in shallow snow areas. These layers have become less of a concern in the vast majority of locations. Last Saturday the mid- December layer is thought to have failed in several large avalanches that occurred in the Bonnington Range. This is a lingering layer of concern that reflects low probability but high consequence. Snowpack depths in the region are around 240 cm.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.