Regions
Northwest Coastal.
We are not sure how the snowpack is reacting to the 20 to 60cm of snow that fell over the weekend. Tread cautiously out there as you continue to gather information about the storm, wind and deep slabs that exist in our early winter snowpack.
Confidence
Moderate - Wind speed and direction is uncertain on Wednesday
Weather Forecast
The Northwest Coast is expected to be relatively cool and dry for the forecast period as a more zonal pattern favors the regions along the 49th parallel. Dribs and drabs of snow are possible on Monday before yet another ridge takes over for the foreseeable future.MONDAY: Broken cloud cover, freezing level around 500m, moderate west/southwest wind, 1 to 5cm of snow. TUESDAY: Sky clearing through the day, freezing level at valley bottom, light variable wind, no new snow expected.WEDNESDAY: A few clouds, freezing level around 400m, strong to extreme northwest wind, no new snow expected.
Avalanche Summary
On Saturday several size 1 to 1.5 wind slabs were observed in steep terrain. Poor visibility likely limited observations, it is expected that a natural avalanche cycle occurred during the storm.
Snowpack Summary
The region picked up 20 to 60cm of storm snow over the weekend accompanied by winds out of the southwest, west, northwest, and even a bit of southeast. This has likely led to the development of a cohesive slab, especially in wind exposed features. These new storm and wind slabs rest on a rain saturated snowpack between valley bottom and 800m. Above 800m, the new storm snow rests on settled old snow, or a melt freeze crust that is 3 to 15cm thick. Below this crust the mid-pack is strong, but there are reports of a feathery surface hoar layer down 50 to 60cm in sheltered locations. There is a second prominent crust that is associated with facets that was buried at the end of October, look for this widespread interface down around 100 to 200cm below the surface.
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.
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.