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, up to 5 cm / west winds 20-40 km/h / alpine low temperature near -11FRIDAY - Mainly cloudy with isolated flurries, 5 cm / west winds 10-20 km/h / alpine high temperature near -9SATURDAY - A mix of sun and cloud / northwest winds 10-15 km/h / alpine high temperature near -10SUNDAY - Sunny with cloudy periods / west winds 10-20 km/h / alpine high temperature near -8
Avalanche Summary
On Thursday, there were preliminary reports of size 1-1.5 loose avalanches, and size 1 human triggered storm slab avalanches.On Tuesday there was one size 1 human triggered persistent slab avalanche reported on a north aspect at 1100 m. It failed on the late January persistent weak layer, 40 cm deep and was triggered remotely (from a distance).Generally speaking, reports from the past week are mainly of wind slabs reacting to ski cuts, with a trend toward smaller (size 1) releases. Small (size 1-1.5) loose dry avalanches have also been observed releasing naturally from steeper, sun exposed slopes in recent days.Reports of human triggered persistent slab avalanches on the January weak layers have been on the decline, suggesting these layers have evolved into a lower likelihood/high consequence avalanche problem.
Snowpack Summary
10-25 cm of new snow sits 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 they may continue to be reactive. There are a two prominent weak layers in the upper snowpack that were buried in mid and late January. These can be found approximately 40-80 cm deep. Both layers consist of surface hoar and may be associated with a crust on steep, south facing slopes. These weak layers have been most reactive at lower elevations, and 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.