Avalanche danger is expected to increase as another intense storm hits the coast.
Confidence
Fair - Due to limited field observationsfor the entire period
Weather Forecast
Friday: Mostly cloudy with flurries bringing 3-5cm. Freezing levels around 500m, and strong northwesterly winds becoming westerlies late in the day. Saturday: A warm intense Pacific frontal system brings heavy precipitation, extreme southwesterly winds, and freezing levels as high as 2000m in the afternoon. Total accumulations are expected to be in the 50-100cm range by Sunday afternoon. Sunday: Freezing levels are expected to drop to 1000m, winds calm down and shift to westerlies, and precipitation is expected to ease off throughout the day.
Avalanche Summary
Recent human-triggered whumpfing and large remote avalanches were reported to be associated with the mid-pack crust/facet complex at upper treeline and lower alpine elevations. I suspect newly formed wind slabs will be very touchy.
Snowpack Summary
There's been over a metre of new snow since Sunday. Fluctuating freezing levels and varying wind and precipitation intensity during the recent storms has probably resulted in various storm snow weaknesses. There was also widespread large surface hoar observed on the previous snow surface at all elevations. A persistent weakness of facets, with an associated crust at upper treeline elevations, can be found down 70-150cm. This weakness seems to be particularly touchy between 1800 and 2000m where it is very sensitive to human triggers and has a high propensity to propagate fractures. Buried surface hoar has also been spotted just below this crust, and sitting on top in some locations. A deeper crust with associated facets and/or depth hoar is approximately 50cm off the ground.
Problems
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.
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.
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.