Regions
Northwest Inland.
Cold, northwesterly winds mark a change in wind direction, which will set up fresh wind slabs in new locations in exposed terrain.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Friday evening: 3-12cm of new snow / Extreme westerly winds / Alpine temperatures of -3Saturday: Lingering flurries in the morning with clearing in the afternoon / Extreme northerly winds / Alpine temperatures of -10Sunday: Clear skies / Extreme northerly winds / Alpine temperatures of -10Monday: Clear skies / Moderate northerly winds / Alpine temperatures of -3
Avalanche Summary
No new avalanches have been reported. Wind slabs will likely remain touchy throughout the forecast period, as sustained winds will redistribute the new low density snow. The additional load of new snow will also keep deeper persistent weak layers reactive, making it possible to trigger larger avalanches.
Snowpack Summary
Snowpack depths in this region are still shallow - around 1 m or so, meaning there are a lot of weak sugary facets in the snowpack at this time. Recent storm snow has been redistributed by the wind, and wind slabs are widespread behind exposed ridges. Where hard wind slabs overlie weak facets, the structure is ripe for human-triggered avalanches. In addition to the sugary facets, you may find a layer of feathery surface hoar (up to 15 mm in sheltered areas), buried around 15-25 cm below the surface. There is another weak layer that formed during the early December cold snap which is now about 40-60 cm deep. A crust from mid-November may be found close to the bottom of the snowpack nestled in amongst the facets. We don't have a lot of information about these layers, but it's worth noting the layer responsible for most of the large avalanches during the big storm just before Christmas was the mid-November rain crust.
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.
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.