A mixed forecast, with some new snow but possibly some sunny breaks, will make this weekend interesting. Even a bit of sun can pack a punch and rapidly increase danger.
Weather Forecast
A series of weather systems are expected to pass through the region over the weekend. Today should be mostly cloudy with flurries. Freezing levels may rise to 1500m, with alpine temps of -1. Light, but gusty SW winds are expected at ridgetop. Up to 10cm are expected by Sat morning. This pattern will continue through the weekend.
Snowpack Summary
On shaded and northerly aspects dry snow exists above 1500m. Soft wind loaded pockets may be forming with moderate SW winds. On solar aspects breakable sun crusts exist, and overlie a series of crusts in the top meter which react with hard planar results in tests. The Feb10 layer is down ~2m, shallower in thin areas, and continues to be a concern.
Avalanche Summary
Yesterday, skiers reported easily triggering small size 1-1.5 slabs, where the storm snow failed on convexities and unsupported slopes. On Wed, loose moist avalanches triggered by skiers when a bit of sunshine provided a lot of warmth. These avalanches ran fast and and far, into mature timber, with some growing to size 2.5.
Confidence
Timing, track, or intensity of incoming weather system is uncertain
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.