Regions
Northwest Coastal.
A succession of storms are expected to keep hazard levels elevated for the next few days. Now is not the time to be venturing into avalanche terrain.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
WEDNESDAY: Snow, accumulation 15-25 cm. Moderate gusting to strong southwest wind. Alpine temperature --2. Freezing level 900 m.THURSDAY: Snow, accumulation 15-20 cm. Moderate gusting to strong southwest wind. Alpine temperature -3. Freezing level 700 m.FRIDAY: Flurries, accumulation 5-10 cm. Moderate gusting to strong south wind. Alpine temperature -4. Freezing level 600 m.
Avalanche Summary
A Size 2, natural avalanche in alpine terrain west of Kasiks River along the Skeena was reported on Tuesday morning. Also on Tuesday skiers in the Shames area reported "hearing a large avalanche" from a valley adjacent to the ski area. In recent days other observers in the Terrace area report shooting cracks within the recent storm snow (see the Mountain Information Network (MIN) post from Nov 25). Looking forward, a succession of storms with high winds and snowfall amounts are expected to continue rapidly loading the snowpack. This will establish very dangerous avalanche conditions during and immediately following these events. Any travel in avalanche terrain will require very conservative route-finding and terrain choices. Please post your observations to the MIN.
Snowpack Summary
Depending on elevation, between 50-100 cm of recent storm snow snow lies on a supportive, 5-10 cm thick crust that formed following last week's warm, wet weather (November 23 crust). Below this crust are two weak layers that were noted to have formed in the early season (November 11 and October 31) and are now buried 120-140 cm within the snowpack. Beneath the October 31 crust is a 20-30 cm thick layer consisting of several thin crusts and large, sugary snow crystals. Recent snowpack tests report easy to moderate, sudden compression test results within the storm snow as well as moderate to hard, sudden results on the October 31 layer near the base of the snowpack.Snowpack depths average 100-170 cm between 800 m and 1200 m elevation in the southern part of the region. In the north near Ningunsaw, reports describe a a much shallower snowpack. Here, a possible 20-30 cm of recent storm snow may now overlie a thin lower snowpack composed mainly of weak, sugary snow. Snow depths in this part of the region range are from 50-100 cm between 600 and 1100 m elevation.
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.