Regions
Northwest Inland.
Give the new snow time to form a solid bond to the surface and remain especially cautious in wind affected terrain.
Weather Forecast
Friday: Mainly cloudy. Light variable winds. Alpine high temperatures around -5.Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Light to moderate southeast winds. Alpine high temperatures of -5.Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate to strong east winds. Alpine high temperatures around -7.
Avalanche Summary
Reports from Wednesday include observations of thin (5 cm) storm slabs becoming highly reactive to skier traffic in the Howson Range, producing small remotely triggered (from a distance) and sympathetically triggered (by an adjacent release) slides. These small slabs were also running naturally in any terrain over a 37 degree incline.Reports from Monday included one remotely triggered Size 1 avalanche on a 50 cm deep surface hoar layer at 1000 m. Although small, this avalanche may be an indicator that the upper snowpack has settled into a more reactive slab.
Snowpack Summary
Snowfall from Wednesday and Thursday brought a variable 10-20 cm of new snow to the region. The new snow has buried a temperature crust left over from warm temperatures on the weekend. This crust likely exists well into the alpine. Beneath the crust, the same warm temperatures also worked to settle 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
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.