This forecast is based on the most storm snow amounts (South and West of the region). The rating would be one step too high for areas that do not get significant amounts.
Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Wednesday night and Thursday: Precipitation tapering off overnight as the system moves across the region. Winds should pick up in the evening to strong speeds from the W and slow down a bit during the day Thursday. Temperatures lowering to around -8 C in the alpine and freezing levels at the surface. Friday: Another system is approaching which should leave some light precipitation during the day with strong W winds that should ease in the afternoon. Similar temperatures are expected. Saturday: More precipitation, cool temperatures and lighter winds from the W.
Avalanche Summary
A couple natural slab avalanches on S-SW aspects size 2.5 were reported in the Northern part of the region. One would have initiated in a shallow/crossloaded feature and would have stepped down from a 5 cm deep surface hoar instability to a 30 cm deep facet instability and then to the old facet/crust combo at the bottom of the snowpack down 85 cm. A skier triggered size 2 slab avalanche was also reported in the central part of the region which would also have initiated in a cross-loaded feature on a NW aspect. Suspect failure on the January 4th surface hoar down around 40 cm.
Snowpack Summary
The new snow will fall on a variety of surfaces; windslabs in the alpine, facets, surface hoar below treeline in sheltered areas and a suncrust on South facing slopes. New windslabs and some sluffing in sheltered terrain is expected. These new layers will most likely be touchy for a certain time.The surface hoar layer below the 40-60 cm of generally well settled snow is still a concern to professionals, especially below 1900 m. in sheltered-shady areas and on S aspects. It still produces sudden planar shears in those areas as well as some resistant planars. A strong mid-pack overlies a weak facet/crust layer near the base of the snowpack, which is now considered inactive.
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.