Regions
Northwest Inland.
Triggering an avalanche is most likely on steep features in wind-affected terrain.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
WEDNESDAY: Flurries developing throughout the day with 10-20 cm of snow by the afternoon, strong south winds, alpine temperatures around -5 C.THURSDAY: Another 5 cm of snow, moderate south winds, alpine temperatures around -3 C.FRIDAY: Mix of sun and cloud, light wind, alpine temperatures around -5 C.
Avalanche Summary
Reports from Monday include two small skier triggered avalanches (both size 1). One was a wind slab on a northwest-facing slope under a wind lip and the other was a remotely triggered avalanche on a 50 cm deep surface hoar layer at 1000 m. These small avalanches may be indicators that the upper snowpack has settled into a more reactive slab.
Snowpack Summary
New snow is falling on a temperature crust left over from warm temperatures on the weekend. This crust likely exists well into the alpine. The warm temperatures also settled the upper snowpack, potentially forming a slab above buried weak layers in the top 50 cm of the snowpack. The potential weak layers include a few crusts and surface hoar layers that formed in early January and December. Recent reports suggest the snow is well bonded to most of these layers, but the recent settlement of the upper snowpack may have changed that.
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.