Continue to make cautious decisions due to the weak layers buried in the snowpack.
Weather Forecast
THURSDAY NIGHT: Mostly cloudy, freezing level 1000 m.FRIDAY: Cloudy with light snowfall, accumulation 5 cm, moderate to strong southwest winds, alpine temperature -3 C, freezing level 1500 m.SATURDAY: Cloudy with light snowfall, accumulation 5 to 15 cm, light southwest winds, alpine temperature -3 C, freezing level below valley bottom.SUNDAY: Cloudy with light snowfall, accumulation 5 cm, light east winds, alpine temperature -24 C, freezing level below valley bottom.
Avalanche Summary
On Wednesday, a skier triggered a small slab at treeline on a west to northwesterly aspect. On Tuesday, a small avalanche triggered by a snowmobile was observed, releasing on the surface hoar layer described in the Snowpack Summary. Shooting cracks were also observed, suggesting instability with that layer.
Snowpack Summary
New snow will begin to fall on Friday with an incoming storm. The snow will fall with strong southwest winds, so expect wind slabs to begin to form in lee and cross-loaded terrain features.The new snow will continue to build a slab over a weak layer of feathery surface hoar crystals, which is buried about 10 to 30 cm. The surface hoar is most prominent between 1500 and 1900 m but has been found up to 2100 m. On south aspects, the snow overlies a melt-freeze crust to the top of the mountains.The middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains.
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.