The upper snowpack is touchy, complex and sensitive to human triggering. Warm temperatures are on route with wet and windy weather for the next 48hrs.
Weather Forecast
Wet flurries, rising temperatures and moderate SW winds are forecast for today, perfect for rising avalanche danger as the load increases over weak layers. Freezing levels are expected to rise to 2700m with 5mm of rain on Friday. Alpine temperatures are expected to stay above freezing Thursday afternoon through Friday with wind gusting up to 80km.
Snowpack Summary
We have 60cm of storm snow at and above treeline and it is settling into a surface slab. Below the surface slab are a sandwich of crusts, surface hoar and facetted layers that are building reactivity to light loads such as skiers. A weak facet layer on top of a crust down 70cm is easily triggered at treeline and is prone to propagation.
Avalanche Summary
Additional load and warming temperatures will increase the sensitivity of the weak layers in the upper snowpack. Convex rolls are reactive to ski cuts triggering slabs on the weak facet layer on top of crust combo. Loose snow sluffing out of steep terrain has also been enough load to trigger this layer.
Problems
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.
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.