Storm slabs on steep slopes, wind slabs on lee slopes, and a persistent slab that seems to be "waking up" on southerly slopes. There's lots to think about, and manage!
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
An approaching Low and associated weak front should only bring light snow Wednesday afternoon and overnight with winds backing to the south for the next couple of days.THURSDAY: Light snow with moderate east winds. Treeline temperatures around -5 to -10 CFRIDAY: More snow overnight Thursday and possibly into Friday with up to 10 or even 15 cm possible. However, there's significant uncertainty about the just how much new snow will fall. Having said that, highest amounts will be in the south, less as you go north towards Nakusp or Revelstoke. Light to moderate southerly winds.SATURDAY: trace to a few centimetres of snow, light and variable winds, treeline temperatures of around -10 C.
Avalanche Summary
Recent avalanche activity has consisted of mainly loose dry sluffing, storm slabs, or wind slabs (skier triggered and skier remote) in the size 1to 2 range. However, we've also received reports of persistent slab avalanches recent accumulations have been the highest. These avalanches, were remotely triggered (from a distance) or naturally occurring. We suspect the buried sun crust buried mid-February is the culprit with those on southerly aspects. Deep persistent avalanche activity has become less frequent over the past week.
Snowpack Summary
Around 20 to 40 cm of recent storm snow is being redistributed into deeper, reactive slabs in wind-exposed terrain. It also covers old surfaces including faceted powder, a sun crust on solar aspects, and surface hoar on shady slopes. Around 50 to 80cm below the surface there's a layer buried mid-February that's a sun crust on solar aspects, and spotty surface hoar on sheltered slopes. This layer looks most concerning on on solar aspects where it's associated with with small facets or surface hoar above. It also seems more of a problem in southern areas of the region.There are several deeper layers that have shown signs of improving but still remain suspect as low probability - high consequence avalanche problems. I'm talking about surface hoar layer buried back in December and January. Near the base of the snowpack is a November crust combined with loose sugary snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall, smaller avalanches coming down from above); human triggering is also possible in shallow, rocky terrain.
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.