Weather Forecast
Thursday night and Friday: Precipitation associated with the upper low will ease off and give place to a light, cool and dry northerly flow. Trace amounts are expected on Friday with light North winds and temperatures around -6 C in the alpine. Overcast skies starting to clear in the afternoon and freezing levels rising to 1300 m.Saturday: High pressure brings dry conditions, mainly clear skies, light NW winds and freezing level rising up to 1400 m. in the afternoon. Sunday: A frontal system approaches from the North coast Saturday night weakening as it hits the interior but could leave some light precipitation amounts, slightly cooler temperatures and winds switching from the SW.
Avalanche Summary
An avalanche size 3 was naturally triggered in the past 48 h. on a steep SW facing slopes with a 100 cm deep fracture line. A few size 1 loose dry avalanches were reported in the new snow. SSL in alpine lee features are also reactive to explosives creating size 1, not propagating very far.
Snowpack Summary
Around 10 cm of new snow fell recently on the previous 40 cm of storm snow, older windslabs, a suncrust on S facing slopes and on a temperature crust below 1700 m. The new snow is sluffing easily with skier traffic and soft slabs could be triggered in alpine in wind effected areas on lee ridgetop features. Buried beneath (60-90 cm) exists a surface hoar and a sun crust layer, which continue to be lingering concerns. On solar aspects, the sun crust seems to be more reactive. Large looming cornices exist on ridgelines. Cornice fall could trigger a large slab avalanche on the slope below, especially when the sun comes out on Friday afternoon and Saturday. The sun and temperatures increasing tomorrow could weaken the snowpack especially on S facing slopes.
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.