Regions
Northwest Coastal.
Moderate winds have loaded lee features in exposed terrain and isolated pockets of storm slab may be lingering on steep slopes.
Weather Forecast
MONDAY: flurries with accumulations of up to 5cm overnight and 3cm through the day, light to moderate westerly winds, 1000m freezing level. TUESDAY: isolated flurries possible with a clearing trend, moderate westerly winds, 1200m freezing level. WEDNESDAY: mainly sunny, light southerly winds, 1200m freezing level.
Avalanche Summary
Natural avalanche activity had slowed before Sunday's storm. A couple of recent standout avalanches from the North of the region are worth keeping in mind though. On Wednesday two very large wind slab avalanches are suspected to have run on the early February crust in the Bear Pass highway corridor. On Saturday a ski cut on a shallow unsupported roll produced a smaller avalanche, again on the early February crust. No new avalanches had been reported on Sunday when this bulletin was published. However, I suspect that there was a cycle of natural avalanche activity through the day given the moderate snowfall and wind.
Snowpack Summary
New snow and moderate winds have created fresh storm slabs at all elevations and wind slabs at treeline and in the alpine. Up to 50cm of new snow now sits above old wind effected snow, a crust on sunny aspects, or surface hoar in isolated sheltered and shady locations. An old crust buried around February 12th that extends up to about 2000m can now be found down 60-80cm. Below this, a layer of surface hoar buried late in January remains a lingering concern in the far North of the region. The snowpack at lower bellow treeline elevations may now be too shallow for avalanches in many places.
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.