A sudden change in weather can have surprising effects on the snowpack. Conservative terrain use is key.
Weather Forecast
MONDAY NIGHT: Snow starting in the afternoon with trace accumulations in the south and up to 10 cm of new snow overnight in the north, wind increasing to moderate from the southwest, temperatures increasing overnight.TUESDAY: Snow continuing throughout the day with another 5-15 cm, moderate southwest winds, freezing level rising with alpine temperatures around -2 in the north and -5 in the south.WEDNESDAY: Flurries with another 5-10 cm of new snow, moderate south winds, freezing level rising to around 1500 m throughout the region.THURSDAY: Cloudy with isolated flurries, moderate southwest winds, freezing level around 1500 m.
Avalanche Summary
Avalanche reports from the weekend included several size 1 loose dry avalanches on a variety of aspects, and a few isolated size 1.5 wind slabs triggered on northeast aspects by explosive and natural triggers. On Tuesday, expect the new snow to build fresh and touchy storm slabs. Warming and loading will also increase the likelihood of triggering persistent slab avalanches.
Snowpack Summary
Expect 10-20 cm of new snow on Tuesday with greater accumulations in the northern part of the region. The new snow, wind, and warming will build touchy storm slabs that will be extra thick and reactive on wind-loaded features. In sheltered areas, the new snow is burying a layer of feathery surface hoar that may produce surprisingly wide propagations. The main concern deeper in the snowpack is a layer of sugary facets from mid-December that can be found between 50 and 100 cm deep. This layer was considered dormant during the recent cold weather, but may become reactive as warm temperatures soften the overlying slab.
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.