Regions
Northwest Inland.
Use extra caution this holiday weekend as weak layers near the bottom of the snowpack have been very touchy. Stick to mellow terrain and avoid steep and convex slopes.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
SUNDAY: Increasing cloud with afternoon flurries, southwest winds picking up throughout the day reaching 40 km/h by the afternoon and reaching 80 km/h overnight, temperatures around -15C.MONDAY: Stormy with accumulations of 5-15 cm, strong southwest winds, temperatures around -10C.TUESDAY: Flurries with trace accumulations, moderate west winds, temperatures around -10C.
Avalanche Summary
Persistent slabs have been very touchy in areas with thin snowpacks, as several size 1.5-2 avalanches have been remotely triggered the past few days. The avalanches have released on weak facets near the ground in steep shallow start zones. Remote triggering is a sign of a serious weakness deep in the snowpack and indicates that persistent slab avalanches may be triggered with very light loads. Also, strong winds with new snow will continue to develop wind slabs throughout the region on Sunday. Overall, human triggering remains likely, especially in terrain that has not been heavily ridden.
Snowpack Summary
Clear cold weather has limited the settlement of recent storm snow and resulted in the formation of new surface hoar and surface facets. Last week, extreme winds formed hard wind slabs behind exposed terrain features. Elsewhere, up to 50 cm of low density snow sits over a highly variable interface comprised of wind-scoured surfaces, hard wind slabs, faceted (sugary) snow, and feathery surface hoar in sheltered areas. The new snow appears to have bonded poorly to this interface. The snowpack is still shallow throughout the region and widespread faceting of the entire snowpack is likely in most areas. A thick rain crust that formed in early November is probably near the bottom of the snowpack and is likely surrounded by sugary facets. Basal facets and depth hoar (more sugary crystals) right at the bottom of the snowpack are reportedly widespread.
Problems
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.
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.