Danger ratings are based on snowfall starting early Wednesday. If it starts later, they would be one step too high for Wednesday.
Confidence
Fair - Timing of incoming weather is uncertain on Wednesday
Weather Forecast
Tuesday night and Wednesday: The frontal system is pushing its way into the interior and precipitation should start around Wednesday morning. Around 10 mm is expected to fall during the day with moderate to strong winds from the SW in the alpine. Freezing levels will lower to valley bottom and the inversion will disappear. Thursday: A break before the next system. Expecting some clearing, winds tapering off staying from the same direction, temperatures also staying cool and freezing level to valley bottom.Friday: Expecting light precipitation and moderate SW winds.
Avalanche Summary
A few recent loose snow avalanche on steep terrain as well as a couple small natural slab avalanches on N and NE aspects were reported.
Snowpack Summary
Storm snow accompanied by strong SW-W winds is creating loose snow concern in sheltered areas and new wind slabs in the alpine and at treeline on lee slopes. These new layers will most likely be touchy for a certain time and could also put on the needed load to awake the deeper instabilities that have been unreactive to skier traffic lately. The new snow will be sitting on a variety of surfaces; sun crust on S facing slopes, surface hoar layer and facets in sheltered areas and windslabs in the alpine and under ridges at treeline. The early January surface hoar layer found under the top 50-70 cm, which has been unreactive to skier traffic but still producing sudden planar shears especially under the elevation of 1500 m. in sheltered areas, could become more reactive with this added load. Under these concerning layers, 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.