Very dangerous avalanche conditions exist in the Columbias. The situation will likely get worse before it gets better and travel in avalanche terrain is not recommended. A Special Public Avalanche Warning is in effect in this region.
Weather Forecast
Friday night: Flurries bringing 5-10 cm of new snow. Light southwest winds.Saturday: Cloudy with continuing isolated flurries and a trace of new snow. Light southwest winds. Alpine high temperatures to -5, rising overnight.Sunday: A mix of sun and cloud with thicker valley cloud due to a temperature inversion. Light south winds. Freezing level rising to 1800 metres with alpine high temperatures to +2. Cooler at lower elevations.Monday: A mix of sun and cloud with thicker valley cloud due to lingering temperature inversion. Light southeast winds. Freezing level to 1800 metres with alpine high temperatures to +3. Cooler at lower elevations.
Avalanche Summary
Reports from Thursday show a continuation of recent heightened avalanche activity involving both storm slabs above the January 5 surface hoar layer and, to a somewhat lesser extent, the deeper December 15 surface hoar. Avalanche activity on these interfaces continues to be extensive, with natural and remote (from a distance) triggers forming a large percentage of observations. Sizes have ranged from Size 1-3, slab depths have generally ranged from 40-80 cm, and activity is being observed on all aspects and elevation ranges. Deeper releases on the December 15 layer have been focused at treeline and below. Reports from the previous two days showed similar activity.Some of the 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.Looking forward, expect a continuation of heightened human triggering potential that will likely increase over the weekend with forecast warming.
Snowpack Summary
Recent storms brought 50-70 cm of new snow to the region. This storm snow sits on surface hoar on sheltered slopes as well as sun crust on steep solar aspects. Numerous storm slab avalanches resulted as the new snow formed a slab before bonding to the surface. Moderate to strong southwest winds have accelerated this slab formation at higher elevations.As the new snow continues to consolidate, it progressively forms a dangerous slab above several persistent weak layers that exist in the snowpack. The first of these is the (January 5) surface hoar that covered the old snow surface. Recent snowpack tests and avalanche activity show high reactivity at this layer. Below it, another surface hoar layer from late December 26 is showing increased involvement in 'step' down releases in the region. This layer is found at similar depths, but just below the January 5 interface.Below these layers, the December 15 surface hoar is now buried 70 to 110 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. Its reactivity has been most apparent at treeline and below.
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.