Confidence
Fair - Due to the number of field observations
Weather Forecast
A strong Arctic air mass will continue to dominate conditions in the southern interior. Friday: Mostly sunny, light NE alpine winds, alpine temperatures -20 to -25CSaturday: Mostly sunny, light-moderate NE alpine winds, alpine temperatures as low as -30CSunday: Increased cloud cover, moderate alpine winds, alpine temperatures as low as -25C, very light snowfall possible
Avalanche Summary
Fewer natural avalanches are occurring in the region but a few natural slab avalanches up to size 2 have been reported. These are both wind slabs and previous storm snow sliding on the late-November crust/surface hoar interface.
Snowpack Summary
Snowpack depths are typically 100-140 cm at treeline elevation. The previous storm snow (~30-60cm) overlies the late-November interface which typically consists of sun crusts on steep south facing slopes and surface hoar in sheltered areas. These weak layers are expected to be persistent and will continue to create avalanche problems in areas with enough overlying snow. The current cold temperatures will contribute to the persistence of this weak layer. Strong NE winds after the storm have caused reverse loading and wind slab formation on SE through W aspects in wind exposed areas. There are two layers of concern within the mid/lower snowpack but these have recently become inactive: the early November surface hoar is roughly 60cm above the ground and the October rain crust is at the base of the snowpack. While these layers have recently become inactive, residual risk of large, destructive avalanches exists, especially in areas with a thinner snowpack. The October crust can be found in the alpine on north aspects and the early November surface hoar appears to be isolated and drainage specific.
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.