Regions
Northwest Inland.
The deep persistent slab problem is more likely in shallow snowpack areas that have developed a slab over basal facets.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Overcast with a chance of flurries and moderate southwest winds overnight and freezing at valley bottoms. Overcast with a couple of cm on Wednesday combined with moderate-strong southwest winds and freezing at valley bottoms. Strong southwest winds combined with 3-5 cm of new snow on Thursday as the freezing level rises to about 1000 metres. Strong southwest winds combined with 5-10 cm of new snow on Friday with freezing levels climbing up to about 1500 metres; uncertainty with the forecast for Friday, this may be limited to the north and west of the region.
Avalanche Summary
A few large avalanches up to size 3.0 were remotely triggered in the Kispiox area on Monday on south thru west aspects at 1700-1800 metres. These avalanches were about 80 cm deep and are suspected to have released on the December 25th surface hoar.
Snowpack Summary
5-20 cm of settled storm snow sits above a widespread rain crust up to about 1300 m. Recent winds have likely formed wind slabs on lee and cross loaded features. Several buried surface hoar layers have been reported 40-80 cm deep and have given variable results in snowpack tests. Many areas have hard slabs in the upper snowpack above weak sugary snow near the ground. Triggering a deep persistent slab above this sugary snow will remain a low probability high consequence scenario for some time.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.