A Special Public Avalanche Warning is in effect in this region.Rapidly warming temperatures Sunday may initiate natural avalanche activity and further increase the likelihood of large human triggered avalanches.
Weather Forecast
A strengthening ridge is pushing warmer and warmer air into BC's Interior and the amplitude of the wave is quite dramatic. The result is something that we're becoming all too familiar with this season, inversion. Cold air in the valleys and warm temperatures in the alpine are expected through at least Tuesday. An unruly low-pressure system approaching the coast Wednesday should shake up the snow globe once againSUNDAY: Scattered cloud, freezing level at valley bottom with above freezing temperatures between 1700 m and 3000 m, light variable wind, no snow expected. MONDAY: Scattered cloud, freezing level at valley bottom with above freezing temperatures between 1700 m and 3000 m, light south wind, no snow expected. TUESDAY: Increasing cloud cover, freezing level at valley bottom with above freezing temperatures between 1000 m and 3000 m, moderate south/southeast wind, no snow expected.
Avalanche Summary
Widespread avalanche activity occurred Friday with numerous reports of slab avalanches reacting to both explosive control work and human triggering. All aspects have been involved as avalanches to size 2.5 continue to run on the January 5th interface. Reports of ongoing remote triggering (from a distance) speak to the reactivity of this interface. On Thursday avalanche activity involved both storm slabs on the January 5th surface hoar and persistent slabs failing on the December 15th interface. Sizes ranged 1 to 3, with slabs 40 to 80 cm in depth on all aspects/elevations. Deeper releases on the December 15 layer have been focused around treeline and below. Reports from the previous two days showed similar activity.Some of the notable themes that are emerging from recent activity include accidental and remote triggering, 'step down' release types, releases on surprisingly low angle, supported terrain, and wide fracture propagations.
Snowpack Summary
Over the last week the region has has received 40 to 70 cm of new snow which rests on surface hoar on sheltered slopes as well as sun crust on steep solar aspects. Numerous storm slab avalanches have resulted as the new snow formed a slab before bonding to the surface. Moderate to strong southerly winds accelerated slab formation at higher elevations.As the new snow continues to consolidate, it progressively forms a dangerous slab above a number of persistent weak layers that exist in the snowpack. The first of these is the January 5th surface hoar down 40 to 70 cm below the surface. Recent snowpack tests and avalanche activity show high reactivity at this layer. Below it, the December 15 surface hoar is now buried 50 to 100 cm deep. This layer has been the failure plane in many recent destructive slab avalanches, with many of these 'stepping down' to this layer from shallower releases. This layer has been most reactive at treeline and below.Deeper in the snowpack, down about 90 to 150 cm, a rain crust from November has shown less reactivity in recent snowpack tests. It is considered dormant but could be triggered in thin spots around variable snowpack areas in the alpine.
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.