Regions
Northwest Coastal.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
A fast moving front will spread some precipitation Friday night and Saturday before the ridge of high pressure rebuilds on Sunday..Saturday: 10-15 cm new snow expected with freezing levels around 1000 m. Ridgetop winds 50-70 kméh from the south.Sunday and Monday: Dry, with a mix of sun and cloud. Freezing levels around 800 m. Winds light southwesterly.
Avalanche Summary
There was an avalanche cycle the ended on Wednesday producing avalanches up to size 4 on all elevation and on all aspects. Most of these avalanches ran on the early January surface hoar layer buried under the storm snow at treeline and below treeline; some of the larger ones ran on the deep persistent basal facet layer in the alpine in the Northern part of the region.
Snowpack Summary
Recent warm temperatures have settled the recent storm snow that ended around 13-14th January, which was previously very reactive on a layer of surface hoar (particularly between 900 and 1400 m) buried around 1 m deep. Weak basal facets near the base of the snowpack were also reactive during this time, particularly in the north of the region. These are found in the alpine and at treeline under over 2 m of snow in some areas. The deep persistent layer at the base of the snowpack is also found in the Southern part of the region, but appears to be less reactive.Extensive wind slab formed on lee and cross-loaded slopes during the SW winds associated with the last storm.
Problems
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.
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.