Although most of the avalanche activity observed on Wednesday was in the alpine, concern still exists for isolated areas at treeline where a touchy interface has caused some dramatic propagations and close calls in the past week.
Weather Forecast
Cool temperatures, with freezing levels remaining below 1000m for Wednesday then a gradual warming trend towards the weekend. Southwest wind, gusting to moderate. Light scattered flurries amounting to less than 5cm by Friday evening, increasing in intensity over the weekend with some models showing as much as 25cm.
Snowpack Summary
New windslabs have formed in the alpine and at treeline, mainly on North Easterly aspects below ridge crests and cross loaded terrain. These slabs add load to a mainly weak and facetted midpack that has a layer of concern down about 60cm at an interface of facets and new snow. Isolated pockets of decomposing surface hoar at treeline down 40cm.
Avalanche Summary
Lots of natural avalanche activity on Wednesday, mainly slab avalanches to size 2 on steep solar aspects between 1500 - 2500m, as well as numerous point releases to size 1.5, mainly on Westerly aspects.
Confidence
Due to the number of field observations
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.