Regions
Northwest Coastal.
Avoid all avalanche terrain. The incoming storm will produce large avalanches.
Weather Forecast
SUNDAY NIGHT: Stormy with 10-20 cm accumulations and extreme southwest winds reaching 100 km/h at ridgetop.MONDAY: Stormy with accumulations of 20-30 cm, extreme 100 km/h southwest winds, temperatures around -10C.TUESDAY: Stormy with accumulations of 10-15 cm, 50 km/h west winds, temperatures around -10C.WEDNESDAY: Flurries with accumulations up to 10 cm, 50 km/h southwest winds, temperatures around -10C.
Avalanche Summary
No new avalanches were reported in the southern part of the region on Saturday. In the northern part of the region, a size 3 avalanche was triggered with explosives. This avalanche failed on weak facets at the base of the snowpack, the same layer that skiers were remotely triggering avalanches on earlier in the week.On Monday, the new snow will form very touchy storm slabs. Storm slabs will be extra reactive in sheltered areas where they are burying a new surface hoar layer. The additional load of the new snow may also reawaken persistent weak layers buried about 1 metre deep. These layers produced large natural avalanches during last week's storm, and now there's some uncertainty as to how reactive they'll be during this storm. If they do release, the resulting avalanches will be very large and destructive.
Snowpack Summary
Expect 20-50 cm of fresh storm snow by Monday afternoon, with extreme winds forming extra deep pockets. The storm snow will bury a layer of feathery surface hoar (up to 15 mm in sheltered areas), making wide propagations possible. A weak interface that formed during the early December cold snap can be found buried about 1 metre deep. The layer consists of weak faceted (sugary) snow, and preserved surface hoar in sheltered areas. The lower snowpack is well consolidated in deep snowpack areas. However, in areas with less snow, such as the northern parts of the region, there are also deeper layers of concern. These include a layer of surface hoar that was buried in mid-November and an old rain crust near the bottom of the snowpack that may have developed weak facets.
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.