Regions
Northwest Coastal.
The recent snowfall has produced numerous large natural avalanches. Choose conservative terrain to stay safe during this instability period.
Confidence
Fair - Due to the number and quality of field observations
Weather Forecast
A fast-moving cold front will arrive on the North Coast on Thursday afternoon bringing more precipitation. Rain at lower elevations and snow above 1500 metres. Freezing level should drop to 700 metres late Thusday night, or early Friday morning.
Avalanche Summary
Reports of natural avalanche activity up to size 3 between 700 and 1700 metres on s facing slopes. Explosives testing in the region has produced numerous size 1 to 2 avalanches suspected to fail on the Dec. melt-freeze crust and facets associated with this layer.Wind loaded slopes reactive to skier triggering.
Snowpack Summary
Strong winds have redistributed the recent storm snow into wind slabs, and rain is saturating the surface of the snowpack at treeline and below. Above treeline, a buried surface hoar layer 10-20cm below the surface has been reported. The mid-December crust/facet layer exists throughout the area where it hasn't been wiped out by recent avalanche activity. The November crust near the bottom of the snowpack is generally well bonded but may still be reactive in areas with shallow snowpack.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.