Purcells

On Friday we received reports of a widespread natural avalanche cycle to size 3.0 that had occurred during the previous 48 hour period. It's suspected that these avalanches initially failed on the January 5th interface before stepping down to the mid-December and late November weak layers. Control work Friday produced both storm slab and persistent slab avalanches on north and east facing alpine features.

On Thursday explosive control work produced mainly storm slabs from size 1.5-2 on all aspects in the alpine. One remote triggered Size 1 persistent slab was also reported.

Wednesdays's reports included observations of several persistent slab releases from Size 1-2.5 that were primarily triggered remotely (from a distance) and failed at the December 15 interface. Several other storm slabs and wind slabs were also reported.

Some of the themes that are emerging from recent activity both in the Purcells as well as in neighbouring regions include accidental and remote triggering, 'step down' release types, releases on surprisingly low angle, supported terrain, as well as wide fracture propagations.

Recent storms brought a variable 10-60 cm of new snow to the region. The new snow sits on surface hoar on sheltered slopes as well as sun crust on steep solar aspects. Moderate to strong southwest winds accompanied the snowfall at higher elevations, creating wind slabs in lee features.

As the new snow continues to consolidate, it is forming a dangerous slab above several persistent weak layers that exist in the snowpack. The first of these is the surface hoar found at the old snow surface. Recent snowpack tests and avalanche activity show high reactivity at this layer. Below it, the December 15 surface hoar is now buried a widely variable 40-100 cm deep. This layer has been the failure plane in many recent destructive slab avalanches in neighbouring regions and its reactivity has been most apparent at treeline and below. In the Purcells, both of these layers are of greatest concern in areas that received greater snowfall from recent storms.

Deeper in the snowpack, down about 90 to 150 cm, a rain crust from November is showing reduced reactivity in snowpack tests. This layer is considered dormant but it may be triggerable in thin spots around variable snowpack areas in the alpine.

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 again

SUNDAY: A few clouds in the morning, clearing throughout the day, freezing level at valley bottom with above freezing temperatures between 1800 m and 3000 m, light variable wind, no snow expected.

MONDAY: Scattered cloud, freezing level at valley bottom with above freezing temperatures between 2000 m and 3000 m, light south wind, no snow expected.

TUESDAY: Increasing cloud cover, diminishing inversion, warmer temperatures should make it to valley bottom, moderate west/southwest wind, no snow expected.