Very dangerous avalanche conditions exist in the backcountry. Avoid all avalanche terrain!
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
Synopsis: Starting Thursday night, a Pineapple Express will bring moisture to this region through the forecast period. Due to the narrow moisture stream, some areas may see more or less than the stated amounts below.Thursday night. 10-15 cm new snow, with the possibility of local enhancement. Very strong SW winds.Friday: Heavy snow/rain, up to 30 cm/mm. Even higher accumulations possible in western upslope areas. Freezing level around 1600 m. Southwesterly ridgetop winds to 70 km/h.Saturday: Moderate snow/rain (around 10 cm/mm), higher amounts possible. Freezing level around 1600 m. Southerly winds around 30 km/h.Sunday: Moderate to heavy snow (15-20 cm). Freezing level around 1500 m. Light winds.
Avalanche Summary
On Tuesday, a cornice fall triggered a size 3.5 avalanche on a northeast aspect, which ran for 800 m. Other natural and explosice-triggered avalanches were observed up to size 3 on a range of aspects. On Wednesday, a few size 2 natural avalanches were observed in steep terrain.
Snowpack Summary
40-70 cm of recent storm snow forms the upper layer of the snowpack. Strong southwest winds have redistributed the new snow into deep wind slabs on exposed lee slopes and cross-loaded gully features. The February 12 persistent weak layer (crust, and/or surface hoar) is now down 60-80 cm. It is primed for triggering and has been reacting readily to both natural and human triggers on all aspects and a wide range of elevations. The effect of a large storm on the snowpack, particularly one accompanied by warm temperatures, wind and possibly rain, will be dramatic. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. These deeper layers have not been reactive to the weight of a rider, but they could potentially be triggered during the upcoming storm, further increasing the potential size of avalanche events.
Problems
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.
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.