Avalanche Forecast

Moderate - Due to the number of field observations

Thursday: Mainly clear skies / Moderate to strong northwest winds / Alpine temperature of -18Friday: Overcast skies with light flurries / Moderate to strong westerly winds / Alpine temperature of -12Saturday: 3-8cm of new snow / Light and variable winds / Alpine temperature of -14

We have received no new reports of avalanche activity, although that may speak more to a lack of observations rather than actual conditions. I suspect there was a round of storm slab avalanche activity in response to Tuesday night's storm. A very large, widespread natural avalanche cycle up to size 4 was observed last week. Slopes of all aspects and elevations ran full path and reached valley floor. In some cases, mature timber was destroyed. Many of these failed on persistent weak layers mentioned in the snowpack discussion. Although natural avalanche activity on these layers has tapered-off, human triggering of very large avalanches remains a very real possibility.

By Wednesday morning up to 25cm of new snow had fallen. Wind data has been sparse, although I suspect strong winds shifted these accumulations into deeper, reactive slabs in wind-exposed terrain. These accumulations overlie a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects and surface hoar on sheltered slopes.Below the snow surface, several persistent weak layers make up a troublesome snowpack. In the top 1-1.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find at least one of these layers on all aspects and elevations.Deeper in the snowpack (120-200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.