Regions
Kootenay Boundary.
We're dealing with a complex snow pack and a significant warming trend. Solar radiation will drive the avalanche conditions for the next couple of days. Use extra caution if you see signs that the sun is starting to warm up the snow.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Monday
Weather Forecast
No precipitation is expected for the forecast period. A strong temperature inversion will develop overnight on Sunday with an above freezing layer forming in the alpine as warm air overrides cool air trapped in the valleys. Valley cloud will linger although there is some uncertainty as to how high it will reach. MONDAY: mainly sunny in the alpine, a freezing level rising to 3500m,and moderate westerly winds. TUESDAY: sunny in the alpine, a freezing level of 3500m, and moderate south westerly winds. WEDNESDAY: sunny with scattered clouds, a freezing level of 2800m, and moderate westerly winds.
Avalanche Summary
Widespread natural avalanche activity, up to size 2, mainly on east through northwest aspects was reported from across the region on Sunday. Wind slabs remain reactive to ski cutting at treeline and alpine elevations. Near Rosland, two size 1.5, skier triggered avalanches have been reported in the last couple of days, releasing between 1800m and 1900m on the late January surface hoar.
Snowpack Summary
Up to 25cm of new snow fell through the weekend and is settling rapidly. Moderate to strong southwest winds have scoured windward slopes and formed stiff wind slabs at treeline and in the alpine. These slabs are still sensitive to human triggering. Around Rossland, the new snow is sitting on a layer of surface hoar down 40cm that is reported to be widespread at treeline elevations. A rain crust can be found in most other parts of the region at this depth. Below this, a thick slab rests on a layer of surface hoar that was buried earlier in January and is now down 80-130 cm. This layer remains a concern in at and bellow treeline, producing sudden planar fractures in snowpack tests under moderate to heavy loads.
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.
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.