Regions
Northwest Coastal.
A significant storm this weekend will result in another major avalanche cycle.
Weather Forecast
An intense storm with a southern moisture feed (a Pineapple Express) is due to hit this region this weekend, bringing 10-20 cm new snow on Saturday and 20-30 mm rain on Sunday. Freezing levels should start out around 700 m Saturday and spike sometime Saturday night/Monday morning to as high as 2000 m. Winds through this storm will be extreme southwesterly. Flurries may continue into Monday, freezing levels will gradually lower to valley bottom by the end of the day.
Avalanche Summary
Several relatively harmless (size 1) human-triggered avalanches were reported to have occurred in the storm snow at treeline elevations on Thursday. On Wednesday, a natural avalanche cycle up to size 3 occurred affecting all aspects and all elevations. Along Bear Pass, 90% of the avalanche paths were reported to have run.
Snowpack Summary
A significant storm dropped 40 to 80 mm of precipitation on this region since Tuesday bring treeline snowpack depths into the 3-4 m range. The storm was accompanied by high winds and touchy fresh wind slabs and storm slabs now exist as a result. A rain crust formed below about 1000 m, which is not lightly buried with new snow. With all the new snow, earlier weak layers are getting rapidly buried to the point where they are hard to trigger. A relatively thin layer of surface hoar or facets was reportedly buried New Year's day - this may have been the focus of some of the storm snow releases during the current storm; however, I suspect this layer will settle out quite rapidly. Lower down, it is still possible to find a surface hoar/crust/facet combo from mid-December. I suspect it would take a very heavy trigger such as a cornice fall to trigger this layer now, although if you are traveling in an unusually shallow snowpack area I'd still be cautious of it. The lower snowpack is generally well settled and strong.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
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.