New snow may not bond well to the older snow surface, especially in wind-loaded terrain. Choose your lines carefully and avoid exposure to terrain traps.
Weather Forecast
Monday: Up to 15 cm overnight then cloudy with sunny breaks and a chance of flurries. The freezing level rises to around 1400 m during the day. Ridge winds are moderate or strong from the W-NW, easing to light during the day. Tuesday: Cloudy with periods of snow 5-10 cm. The freezing level is near 1400 m and winds are moderate to strong from the SW. Wednesday: Cloudy with flurries and sunny breaks. The freezing level rises to 1600 m and ridge winds are light.
Avalanche Summary
Numerous natural and rider triggered wind slab avalanches were reported on Saturday. These thin slabs occurred on a variety of aspects in wind-loaded terrain and were generally 15-20 cm deep. There were also reports of loose snow sluffing on steep north (dry snow) and south (wet snow) facing slopes. There was also a report of a small wind slab that initiated in steep terrain, ran off a cliff, and triggered a size 3 persistent slab on the slope below. This event occurred on a north facing alpine slope.
Snowpack Summary
25-40 cm of new storm snow sits on a crust on solar aspects and lower elevation terrain, and surface hoar on shady and sheltered slopes. Touchy new wind slabs are likely in exposed lee terrain at and above treeline. A weak layer of surface hoar and/or a sun crust buried February 21 is now 40-70cm below the surface. Where it exists, this layer may become reactive to human triggers as the overlying slab develops. The surface hoar and/or crust layer buried February 10 is now down 75-120cm. This layer was less reactive over the weekend with cooler temperatures, but remains a concern for large triggers like cornice falls or a smaller slide in motion. Cornices are large and potentially weak and should be avoided if possible.
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.