Winds have created a variable snowpack. Be alert to conditions that change with aspect and elevation.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Thursday
Weather Forecast
Generally light precipitation is expected on Wednesday, with the freezing level around 1700 m and winds light to moderate from the S to SW. Moderate snow is expected on Thursday and Friday (15-20 cm /day) above about 1600 m (rain at lower elevations). Winds are moderate to strong from the S to SW.
Avalanche Summary
A skier accidentally triggered a size 3 hard wind slab on Monday, which failed on the March crust/facet layer. Skiers also remotely triggered size 1.5-2.5 slabs, most on northerly aspects, some of which failed on the crust/facet layer. A natural and human-triggered cycle of wind slabs was reported on Sunday.
Snowpack Summary
Wind slabs (most recently formed with northerly winds, but previously lee to the S-SW) and wind-affected surfaces are the main theme at the snow surface. Cornices may also be fragile. Older, buried wind slabs may be hard to spot. A crust/facet persistent weak layer, buried anywhere from 10 to 60 cm down, has started to play up (see avalanche summary). Avalanche problems associated with this layer may linger for a while. A deeper crust (formed by heavy rain in February) is down around 70 cm. Below the deeper crust, the snowpack is reported to be generally well-settled and strong. Below treeline, the diminishing snowpack is trending isothermal (same temperature throughout).
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.
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.