Cornices likely got overloaded last night with high to extreme winds. A combination of buried surface hoar and wind slab will make route selection tricky today. Look up, look around, and avoid terrain traps.
Weather Forecast
An unstable air mass will remain over the region for the day, bringing moderate westerly winds and flurries and rising freezing levels to 1100m. An approaching warm front with an upper ridge will build over the area on Thursday and Friday, with moderate to high winds and mild temperatures for the weekend.
Snowpack Summary
A new layer of surface hoar was buried yesterday by 20 cm of new snow. On sunny aspects, this surface hoar layer rests on top of a crust. It is most notable between 1700-1900 m. Below this, the mid-pack is strong, with hard failures in stability tests down 40cm. Surface sluffing and wind slabs can be expected in steep and wind affected areas.
Avalanche Summary
25cm of new snow and high to extreme S. winds have resulted in an avalanche cycle in the park overnight. Most of these were from steep terrain in the highway corridor, and it is likely that similar avalanche activity occurred in the backcountry as well. Avalanches were running to the middle of the fans, and on average were size 2.5 to 3.
Confidence
Due to the number of field observations on Wednesday
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.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.