Smaller wind slabs may step-down to deeper weak layers resulting in large, destructive avalanches.
Summary
Confidence
Moderate - Due to the number of field observations
Weather Forecast
SUNDAY: Mix of sun and cloud, light easterly winds, and treeline temperatures around -20. MONDAY: Mix of sun and cloud, strong to extreme easterly ridgetop winds, and treeline temperatures around -23. TUESDAY: Mostly sunny, light to moderate easterly winds, and treeline temperatures around -15.
Avalanche Summary
Over the past week there have been a couple natural deep persistent avalanches to size 3.5. These are large, destructive avalanches that failed on sugary facets at the bottom of the snowpack and ran long distances.
Snowpack Summary
10-20 cm of recent snow with northerly winds have likely created fresh wind slabs sitting on top buried surface hoar and/or facets. Snow depth at treeline varies from about 1 m in most areas to 2 m at deeper snowpack areas in the south and west of the region, and up to 250 cm in the alpine. The shallow snowpack areas mostly consist of weak facetted or sugary grains beneath hard wind slabs. These wind slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak snow crystals near or at the ground. In addition to the facets, a thick layer of buried surface hoar may be found 20-30 cm below the surface. There is another persistent weakness that formed during the early December cold snap which is now about 40-60 cm deep. A crust from mid-November may be lurking close to the ground nestled in amongst the facets.
jsmith,
Avalanche Canada
