Wind slabs may be reactive to rider triggering. The safest, best riding may be in lower elevation terrain sheltered from the wind.
Confidence
High - Due to the number and quality of field observations
Weather Forecast
SATURDAY: Mix of sun and cloud, light southwest winds, alpine temperatures around -12 C.SUNDAY: Cloudy with sunny periods, light west winds, alpine temperatures around -12 C.MONDAY: Flurries with accumulations up to 5 cm, moderate southwest winds, alpine temperatures around -8 C.
Avalanche Summary
Wind slabs have been reactive to human and natural triggers over the past week. On Thursday, several human-triggered wind slabs in the size 1-1.5 range were triggered on a wide range of aspects at treeline. On Friday, a skier triggered a size 2 avalanche on a south-facing alpine slope in the Valhalla range. The avalanche was likely triggered on the mid-December facets in a relatively shallow snowpack area. Wind slabs will likely remain reactive over the weekend.
Snowpack Summary
Up to 30 cm of low density snow fell earlier this week. Moderate to strong southwest and then northerly winds have shifted these fresh accumulations into reactive wind slabs on leeward slopes. The mid-December facet/surface hoar persistent weakness can be found buried 70-120 cm deep and is generally considered dormant. However, we are still receiving occasional reports of sudden results in snowpack tests, suggesting that it has to potential to propagate into a large avalanche if triggered, particularly in shallow spots where this layer is closer to the snow surface. The lower snowpack is well bonded and features a thick rain crust 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.