Regions
Northwest Coastal.
Wind slabs are growing while a deeper weakness continues to produce large avalanches. Evaluate the terrain and snowpack carefully and stay aware of overhead hazards.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
THURSDAY: Unsettled weather with flurries bringing 5-15 cm of snow, moderate and gusty south wind, alpine temperature around -6 C.FRIDAY: More flurries with 5-15 cm, moderate south wind, alpine temperature around -4 C.SATURDAY: Still more flurries with 5-15 cm, moderate southwest wind, alpine temperature around -6 C.
Avalanche Summary
Reports from Tuesday indicate the persistent slab problem is alive and well throughout the region. A few natural size 2-2.5 avalanches were triggered in the Bear Pass / Stewart area by solar input or cornices. A skier also remotely triggered a size 2 avalanche on the February facet/crust interface on a moraine feature around 1150 m (40 cm deep). Similar activity was reported on Monday, including a size 3 avalanche that was remotely triggered from flat terrain by a snowmobiler north of Stewart. Smaller natural avalanches were also reported on Tuesday, including size 1-2 wind slabs from recent wind loading and size 1.5-2 loose moist avalanches in steep solar-facing terrain.In addition to the ongoing persistent slab problem, the incoming weather pattern is looking to continually build fresh wind slabs.
Snowpack Summary
Fresh wind slabs are forming in the lee of exposed terrain as unsettled weather brings small amounts of new snow and moderate southwest winds. Storm snow from last week is continuing to settle and get redistributed by predominately southerly winds. Old wind slabs may be reactive above a 40 cm deep rain crust. At treeline and above, recent loading has stressed a 50-100 cm deep weak interface composed of facets, crust, and surface hoar from late February. Recent reports suggest this layer is still reactive throughout the region, especially in the north.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.