Conservative decision making and terrain use is the name of the game when these tricky avalanche conditions persist. Check out the new Forecaster Blog @ avalanche.ca.
Weather Forecast
A ridge of high pressure is strengthening a predominant northwesterly flow which will invade the Interior regions. This will bring relatively dry cool air. Ridgetop winds will blow light-moderate from the northwest and alpine temperatures will hover near -12. Skies will likely remain cloudy with some sunny periods Friday and Sunday. Light precipitation is expected Saturday.
Avalanche Summary
On Wednesday, several natural avalanches up to size 2 were reported and results up to size 3.5 were seen with the use of explosives. The buried surface hoar layer remains very touchy to skier/ rider triggers and numerous avalanches size 1-2.5 were reported. I don't expect things to improve over the holiday period and suspect this layer is primed for human triggers.
Snowpack Summary
New snow 10-30 cm fell Tuesday night. In some parts of the region the new snow is sitting on a thin breakable rime crust, but most concerning is the thick persistent slab (40-90 cm) which is sitting on a very touchy surface hoar layer buried mid-December. Below 2100 m this slab sits on a thick, solid crust that has been acting as a perfect sliding layer. Persistent slabs will be very touchy to the weight of a skier and rider, especially in wind effected areas where the slab is stiffer. A hard rain crust with facets from early November is buried over 1 m down and is currently unreactive but triggering from shallow rocky, unsupported terrain remains a concern.
Problems
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.
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.