Regions
South Coast Inland.
Strong SW wind and fresh snow Friday night may fuel a round of natural avalanches while most of us sleep. Light wind and snowfall on Saturday may appear picture-perfect, but the mountains are currently primed for human triggered avalanches.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Saturday
Weather Forecast
A deep upper trough is moving through BC this weekend. A few disturbances are expected to continue to deliver moderate precipitation into southwestern BC through Friday night. As the trough exits Saturday, snowfall is expected to cease as the freezing level drops to valley bottom. Sunday offers a break in the action before modest snowfall begins again on Monday.FRIDAY NIGHT: 5 to 15 cm of snow, strong to extreme southwest wind, freezing level at 1500m, falling throughout the night.SATURDAY: Overcast skies, freezing level near valley bottom rising to about 700m in the afternoon, moderate SW wind, 1 to 5 cm of snow. SUNDAY: Overcast skies, freezing level near valley bottom rising to about 600m in the afternoon, moderate SW wind, no significant precipitation expected. MONDAY: Overcast skies, freezing level around 500m, moderate SW wind, 1 to 5 cm of snow. Visit avalanche.ca/weather for a more detailed mountain weather forecast.
Avalanche Summary
On Thursday skiers triggered wind slabs on both northeast and southeast aspects to size 2, see this great MIN report from Thar Peak Thursday: https://bit.ly/2lFjEQL Reports from Wednesday include several natural avalanches in steep leeward alpine terrain up to Size 2.
Snowpack Summary
Much of the region received 30 to 70cm of fresh snow this week, which has been blown into deep drifts by southerly winds and is bonding poorly to facets and buried surface hoar, as well as crust on previously sun-exposed slopes. The widespread mid-February crust is below all this. In the northern part of the region, a facet/surface hoar weakness buried early February, is now down around a metre and remains reactive in snowpack tests. It is also suspected as the failure plane in at least one of two recent large persistent slab avalanches in the Hurley Pass area. In the Cascades (e.g. Coquihalla), the mid and lower snowpack are well settled and strong.
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.