15-16

One inch of snow on Wednesday night may have softened the skiing and hidden the rocks, but it did not decrease stability. The ski patrols at Big Sky and Bridger Bowl have been testing the snowpack with explosives and ski cuts, and have had minimal avalanche activity to speak of. The Big Sky patrol noted an explosive triggered wind slab that failed on facets in the upper part of the snowpack. Strong winds last night did not have much snow to transport, so fresh wind slabs today are not an issue.

There has been no snow or avalanche activity since Thanksgiving. East winds created a few slabs near the ridgetops, but these are not an avalanche issue any more. The mountains have 1 ½ to 3 feet of snow on the ground. Regardless of depth, cold temperatures are weakening the snowpack (video explaining this process). Thin snow cover and cold temperatures create sugary facets which can grow into large, crumbly depth hoar crystals. The sun is low, the temperatures are cold, the snow is thin and conditions are ripe for facet growth.

Thin snow cover combined with frigid temperatures is not a good recipe for building a strong snowpack. In some areas, the snowpack is completely rotten and faceted, while in others, there’s enough depth and density to ward off the evil effects (for now) that strong temperature gradients produce.

In upper elevation terrain, some slopes are scoured to the rocks while others are heavily loaded with wind blown snow. Wind loaded slopes will be the most likely to produce avalanches. Approach wind loaded slopes with caution, especially in steep, high consequence terrain. Photo GNFAC

Storm totals measured 2-4 inches of powder. There was only .2-.3 inches of snow water equivalency, not enough weight to create widespread instability.  East winds are an unusual direction and typically mean cold temperatures, no snowfall and wind-loading in unusual areas. Yesterday, in the Bridger Range near Wolverine Bowl, skiers were able to trigger small pockets of windblown snow. In many areas these freshly formed wind slabs are sitting on weak, sugary, faceted snow.

Snowfall will continue today in all areas. Easterly winds will transport the new snow and create slabs on west facing slopes. East winds are rare and can create unusual patterns of instability. Look for slabs in uncommon locations such as the west aspect of ridgelines and at mid elevations.

There isn't much snow in Beehive Basin. The snow that is on the ground has been exposed to strong temperature gradients and becoming faceted and weak. This will create a weak foundation for future snowstorms. Photo GNFAC