Regions
Northwest Coastal.
After a big storm, give the snowpack time to settle before venturing out into exposed terrain. Another punchy storm is on its way for Saturday.
Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Around 10 cm new snow is expected overnight and into Thursday morning with the passage of the cold front before a short-lived ridge sets up over the area bringing a temporary reprieve. Winds on Thursday will shift from SW 40 km/h to NW 30 km/hr. Freezing level will be at valley bottom. On Friday, a weak frontal system will bring light precipitation with moderate SW winds. On Saturday, a stronger frontal system will give heavy precipitation (current estimate 30 cm), with freezing levels rising to 1500 m and strong southwesterly winds.
Avalanche Summary
Natural avalanches up to size 3 have been reported during the recent storm, mostly on northeast aspects. Poor visibility and a lack of observers has been hampering observations at higher elevations.
Snowpack Summary
A significant storm dropped 40 to 80 mm of precipitation on this region with high winds and freezing levels going to at least 1500 m. Expect touchy fresh wind slabs and storm slabs from the new snow. Also expect a firm rain crust below about 1500 m. 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.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.