Watch for localized wind slabs in exposed lee terrain.
Confidence
Fair - Due to the number of field observations
Weather Forecast
A weak storm is expected to start on Saturday in the afternoon and persist into Sunday bringing only light amounts to this region. Current models are showing around 5 cm from 4pm Saturday to 4am Sunday with another 2 cm or so on Sunday. Freezing levels are expected to be around 1600 m on Saturday and then rise to around 1800 m on Sunday. Winds are expected to be around 60 km/h from the southwest overnight Saturday and into Sunday. Monday looks mostly dry with freezing levels around 1500 m.
Avalanche Summary
A thin wind slab was triggered on Thursday from an east facing slope in the alpine.
Snowpack Summary
Surface hoar has grown on top of 10-20 cm loose dry snow that has been sluffing readily on a thick hard supportive rain crust that extends into alpine elevations. In the alpine, winds have been conducive to blowing this low density snow into thin wind slabs in exposed lee areas. At treeline and below, the near surface crust is effectively bridging triggers from penetrating to deeper persistent weaknesses that formed earlier in the season. However, on alpine slopes above the recent rain line poorly bonded crusts, facets, and/or buried surface hoar may be susceptible to triggers. Professionals are still concerned with a buried crust from November, down 50-70 cm, that could be triggered by large loads.
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.