Regions
Northwest Inland.
Avalanche danger may be higher in the north of the region, where a buried weak layer has been recently reactive.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
The first of two cold fronts is expected to bring 5-10 cm snow on Friday, with strong south-westerly winds and the freezing level rising to around 1300 m. There is a lull on Saturday before the second front brings light snow and strong winds again on Sunday.
Avalanche Summary
Isolated wind slab avalanches were reported over the last couple of days. In the north of the region, a small natural avalanche that stepped down to the early January surface hoar on Sunday is a good reminder that this layer needs to remain a concern. Deeply buried persistent weak layers in the alpine also woke up in the north of the region over the weekend when several large avalanches released on basal facets. This weak layer was reported to be reactive to skier triggering from thin spots, as well as heavy triggers such as a smaller avalanches or cornice failures.
Snowpack Summary
Recent strong winds have created wind slabs on a variety of slopes at alpine and treeline elevations. Incoming snow will bury wind slabs, a thin sun crust on sunny aspects and surface hoar in isolated sheltered and shady locations. 40-80 cm of snow sits above a melt freeze crust buried around February 12th. This crust extends up to about 2000 m. Below this, a layer of surface hoar buried late in January remains a lingering concern. Shallow snowpack areas may also have a weak base of facets near the ground.
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.