Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

I observed several recent avalanches in the Sherwins today and ventured up toward the perch to do a fracture investigation of one of the more notable slides.

• What I had initially assumed was 3 separate crowns proved to be one large and wide propagating wind slab avalanche. This avalanche initiated at around 9500’ with a slope angle averaging around 35°. It broke loose in a leeward catchment zone on a sparsely treed slope near treeline.
• This avalanche’s Crown height averaged about 30- 50 cm with a max depth of about 3 ft. the crown was about 400’ wide and I would classify this as a D2 in size. It should be noted that terrain features in the flow track encouraged wide and relatively shallow debris piles rather than one confined area which would have made this a more destructive event.
• This avalanche broke on a thin layer of near surface facets and decomposing fragmented grains sandwiched between two 1 f hard wind layers.  I believe this was the 3/18 interface.

Today was quite cold and the wind was ripping leading to copious amounts of blowing snow and subsequent deposition. In fact, in the time it took me to the skin from the propane tanks to the crown, it had almost filled completely back in muffling some of the features.  I also observed reactive wind deposits on favorable terrain features BTL, stiffening surface snow, and heavy drifting in recent skin tracks.

In sun-exposed areas on the moraine, I found a grabby MF crust about 1-2 cm thick which made for a less-than-enjoyable exit back to the tanks.