Regions
Northwest Inland.
Confidence
Fair - Due to the number and quality of field observations
Weather Forecast
Synopsis: A low pressure system in the North Pacific continues to feed moisture into BC .Tonight: Cloudy with flurries, possible 5 to 10 cm of precipitation, freezing level around 500 metres, winds from the west, light, occasionally gusting to strong.Wednesday: Cloudy with flurries, trace of precipitation, freezing level around 700 metres, ridge top winds light from the west, gusting to moderate.Thursday: Cloudy with sunny periods and flurries, trace amounts of precipitation, freezing level around 700 metres, light ridge top winds..Friday: Cloudy with flurries, 5 to 10cm of precipitation, freezing level around 500 metres, winds from the southeast, light to moderate at ridge tops.
Avalanche Summary
Reports indicate the Feb.10th weak layer has been re-activated with recent new snow loading. Commercial operators have reported a widespread natural cycle in the past 24 hrs, and on Sunday a skier controlled size 2 was triggered on the Feb. 10th weak layer, on a north aspect at 1100 metres in the Hankin area. Conditions are primed for rider and sledder triggered avalanches!
Snowpack Summary
Conditions are highly variable throughout the forecast region, with considerably more snow to the west and north. An additional 10 cm of recent 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 layer of faceted snow. This layer is most likely present on protected north slopes at all elevations. There is a sun crust on steep solar aspects, and various wind affected surfaces in exposed terrain. Strong 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 and may have a supportive wind-pressed slab. Moist/wet snow, rain crust or melt-freeze crusts in the upper snowpack are likely, below 1200m. The early February weak layer of facets, crusts, and/or surface hoar is buried down about 60-100 cm. Test results and recent 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.