Regions
Northwest Coastal.
There is low confidence in this forecast due to limited observations. As always, and especially when confidence is low, it is essential to supplement this information with your own observations. And don't forget to post them to the MIN!
Weather Forecast
Expect another 10-30 cm by Wednesday morning (depending on elevation and proximity to the coast) accompanied by strong to extreme southerly winds and freezing levels spiking at around 1400m. Wednesday should be relatively dry, cool and calm with alpine winds easing to moderate westerlies and freezing levels dropping to 600 m. Light snowfall is expected for Thursday with 5-10 cm of accumulation, moderate southwesterly alpine winds, and freezing levels rising throughout the day. The next major system is expected to make landfall early Friday morning with heavy snow, extreme winds and freezing levels as high as 1500 m.
Avalanche Summary
Skiers in the Shames area reported natural and skier accidental avalanche activity up to size 1.5, and skier controlled up to size 2.0 on Friday, but there have been no new reports since then. These avalanches are suspected to have released on a buried layer of decomposing surface hoar that is sitting on a firm supportive crust down about 50-80 cm in the alpine.
Snowpack Summary
Another 10-20cm since Monday morning adds to the 20-50 cm of fresh snow from Sunday. Recent reports from the Shames area suggest a touchy weak layer of surface hoar buried mid-November and is now probably down about 50-80 cm and sitting on a firm supportive crust, making it particularly sensitive to triggers. Some earlier information came from Wesach that suggested the buried surface hoar problem exists there as well. This weak layer has been reactive to light loads like individual skiers and riders. There is very little snow in the north of the region at Ningunsaw and Cassiar. Snow that is on the ground in these areas may be facetting and developing a weak basal layer.
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.