Regions
Kootenay Boundary.
This is the first big warm-up after some significant snowfall. A warming-related avalanche cycle is expected.
Confidence
Poor - Timing or intensity of solar radiation is uncertain
Weather Forecast
Saturday will stay mostly dry, with sunshine and cloud. Winds should remain light. Freezing level should go to around 1800 m during the day. Sunday looks bright, sunny and warm, with freezing levels going up to around 2500 m. Very little overnight cooling is expected Sunday night as clouds move in overnight. Monday will stay warm, with freezing level around 2400 m and some good periods of sunshine.
Avalanche Summary
Several relatively small avalanches occurred in the storm snow on Thursday and into Friday. A fatal avalanche incident occurred in this region on Wednesday. We will post more details when they become available. On Monday and Tuesday avalanche activity was isolated to the recent storm snow. On Sunday a large avalanche occurred in the Lumberton snowmobile area in the East Kootenays: a snowmobiler accidentally triggered a very large (Size 3+) avalanche that resulted in a close call.
Snowpack Summary
10-20 cm new snow on Wednesday night followed a previous 20-30cm of new snow on Tuesday. This new snow has built storm slabs in many places and wind slabs in exposed leeward terrain. A sun crust that recently formed on southern aspects to around 1700 m and a spotty 2-6mm surface hoar on north and east aspects are now buried around 60-100cm. Below that, the more significant early February surface hoar is down 100-180cm. Avalanche activity has become more sporadic on this layer, but ongoing large events indicate it still has the ability to fail, despite how deeply it is buried. A melt-freeze crust, down 20-30cm, below 1800m provides some bridging to the layers below. Below the early February surface hoar layer, the snowpack is strong in most places. Cornices are very large and would act as a significant trigger for all the layers mentioned above if they drop.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.