Regions
Northwest Inland.
Confidence
Fair - Due to the number and quality of field observations
Weather Forecast
Synopsis: A low pressure system in the Gulf of Alaska will feed moisture onto the coast and into the north west interior for the next 4 or 5 days.Tonight: Clearing as precipitation tapers off, freezing level around 1100 metres winds from the north west up to 50 km/hr.Monday: Sunny periods with a few clouds, no precipitation in the forecast, freezing level around 700 metres, winds from the west, 40 Km/hr.Tuesday: Cloudy with flurries, possible 5 to 10 cm of precipitation,, freezing level around 800 metres winds from the south west light occasionally gusting to moderate.Wednesday: Sunny with cloudy periods and isolated flurries, not much precipitation expected, freezing level around 800 metres, winds light from the west, gusting moderate to strong.
Avalanche Summary
Reports from commercial operators indicate the Feb.10th weak layer has been re-activated with recent new snow loading, and on Friday, a natural size 2 slab avalanche released on the early-March weak layer down 30-40cm on surprisingly low angle terrain (25-30 degrees).
Snowpack Summary
Conditions are highly variable throughout the forecast region. An additional 10 cm of storm snow in the Hudson Bay Mtn. area brings the slab to between 40 and 80cm overlying the early-March weak layer of surface hoar and/or a thick layer of faceted snow. This layer is most likely present on shady slopes at all elevations. There is a sun crust on steep solar aspects, and various wind affected surfaces in exposed terrain. Strong southwest winds have created dense wind slabs on exposed lee slopes and in cross-loaded features. In wind exposed areas, the snow surface is reported to be wind scoured or a very supportive wind-pressed slab. Moist/wet snow or melt-freeze crusts in the upper snowpack are likely at lower elevations, below roughly 1200m. The early February weak layer of facets, crusts, and/or surface hoar is buried down about 60-100 cm. Test results and isolated avalanche activity suggest this layer is still reactive to human-triggering. Basal facets and depth hoar remain a concern in areas with thin or variable snow cover.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.