Fresh storm slabs may be reactive to human triggering. Watch for signs of instability such as whumphing, cracking and recent avalanches.
Weather Forecast
THURSDAY NIGHT - Mainly cloudy with isolated flurries, 5-10 cm / southwest winds 20-40 km/h / alpine low temperature near -13FRIDAY - Mainly cloudy with isolated flurrie, up to 5 cm / southwest winds 10-25 km/h / alpine high temperature near -11SATURDAY - A mix of sun and cloud / northwest winds 10-15 km/h / alpine high temperature near -12SUNDAY - Sunny with cloudy periods / northwest winds 10-15 km/h / alpine high temperature near -9
Avalanche Summary
On Wednesday, a size 2 persistent slab avalanche was triggered by a cornice failure on a southeast aspect in the alpine. This avalanche reportedly failed on the late-January persistent weak layer.Observations from the past few days have shown size 1-2 wind slabs releasing with skier traffic on a range of aspects in the alpine and at treeline. Small (size 1-1.5) loose dry avalanches have also been observed releasing naturally from steeper, sun exposed slopes. Persistent slab avalanche activity on the three buried surface hoar layers (described in more detail in the Snowpack Summary) has slowed down, but not stopped. This has evolved into a low likelihood avalanche/high consequence avalanche problem at treeline and below.
Snowpack Summary
10-20 cm of new snow is sitting on wind slabs, surface hoar (feathery crystals) and facets (sugary snow), and a crust on sun exposed slopes. The buried wind slabs are also sitting on facets and may continue to be reactive.There are three prominent weak layers in the upper snowpack that were buried in mid and late January, and early February. They can be found between 30-90 cm below the surface. These layers consist primarily of surface hoar, though they may be associated with crusts on steeper, south facing slopes. These weak layers are most prominent at lower elevations - especially below treeline. The lower snowpack is generally considered to be strong, except for shallow, rocky areas where the cold temperatures continue to facet (weaken) the snowpack.
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.