Regions
Northwest Coastal.
The incoming weather will give little time for storm slabs to heal. Stick to supported slopes and watch for signs of unstable snow such as whumpfs and cracks.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
THURSDAY: Flurries with 5 cm accumulations / moderate southwest wind / alpine temperatures around -6 C.FRIDAY: 10-20 cm of snow / moderate to strong southwest wind / alpine temperatures around -3 C.SATURDAY: 15-30 cm of snow / moderate to strong west wind / alpine temperatures around -1 C.
Avalanche Summary
Preliminary reports of a few large avalanches suggest a widespread natural avalanche cycle occurred during Tuesday's storm.The most recent report of a persistent slab avalanche was on Saturday, when a size 2 avalanche on a buried surface hoar layer was remotely triggered on a northeast aspect in the alpine. Tuesday's storm would have tested the various persistent weak layers in the region, but at the moment we don't have enough observations to know whether or not they layers were reactive during the storm.
Snowpack Summary
Westerly winds and ongoing flurries are likely building fresh wind slabs in exposed terrain. This sits above 50 cm of settling snow from Tuesday's storm, which is likely still reactive to human triggers.A weak layer buried in mid-January remains a concern and is now 60-100 cm deep. In most areas this layer is a crust, but it may also be surface hoar in sheltered areas at treeline and below. Prior to the storm, this layer produced sudden snowpack test results in the Shames area and avalanche activity at upper treeline and alpine elevations. Professionals have also been monitoring another two crust / surface hoar layer that were buried in mid-December and early January that are now 100-150 cm deep. These layers were most recently active in northern parts of the region near Bear Pass.
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.