Regions
Northwest Inland.
Hard wind slab over weak, sugary facets should be treated with respect - it has the right structure to support a large, dangerous avalanche.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
THURSDAY: Light snow, 4-8 cm. Winds 20-30 km/h from the east. Alpine temperatures around -10C. FRIDAY: Dry with some sunny breaks. Northwest winds increasing through the day to 60 km/h by the afternoon. Temperatures around -15C. SATURDAY: Flurries. Strong northerly winds. Temperatures around -10C.
Avalanche Summary
No avalanches have been reported since Monday, when, a skier remote triggered a size 1.5 wind slab in the Hankin area on a north aspect at treeline (see MIN report). Wind slabs will remain touchy throughout the week, 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
Moderate to strong winds continue to redistribute the 10-30 cm of low density storm snow, forming touchy wind slabs in the lee of exposed ridges. The new snow has also buried a layer of feathery surface hoar (up to 15 mm in sheltered areas), making wide propagations possible. There is another weak layer that formed during the early December cold snap which is now about 40-60 cm deep. However, the layer that was responsible for most of the large avalanches during the big storm just before Christmas was the mid-November rain crust. This lies close to the bottom of the snowpack and is associated with sugary facets. Because of the low snow depths (around 1 m), this layer remains very much a concern in this region.
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.