Regions
Northwest Coastal.
Temperatures are forecast to rise significantly early this week. This rapid increase in temperature will result in a spike in avalanche danger. For advice on how to manage these changing conditions please refer to the latest forecaster's blog.
Weather Forecast
Monday: Low cloud with a chance of precipitation. An above freezing layer (AFL) is expected to develop between 1500 and 3000 m. Mountaintop temperatures could reach +5. Winds are moderate from the northwest. Tuesday: Light precipitation (possible freezing rain). The AFL remains between 1000 and 2000 m. Winds are moderate from the northwest. Wednesday: Cloudy with a chance of flurries. The AFL dissipates and the freezing level returns to 1000 m. Winds remain moderate from the northwest.
Avalanche Summary
There are a few reports of glide releases in steep south facing terrain. Explosive control work near highway corridors over the past couple days produced several avalanches up to size 3.5. Some of these slides released on the late December surface hoar or facet layer and propagated widely.
Snowpack Summary
The snow surface consists of wind slab, surface hoar, and weak facetted snow depending on aspect and elevation. Below this 60-90 cm of storm snow from last week continues to settle and gain strength. However, a weak layer of surface hoar or facetted snow sits at the base of the storm snow. Recent snowpack tests give generally moderate sudden planar, or "pops", results on this buried surface hoar layer and indicate potential for wide propagation. Near the base of the snowpack, a crust/facet layer continues to concern local avalanche professionals. This seems most prevalent near Bear Pass where the snowpack distribution is quite variable. This weakness is unlikely to be triggered by a single person, but it remains possible with a very heavy load (e.g. cornice fall) or from a thin-spot trigger point.
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.