Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

It should come as no surprise that stability was deteriorating today as the storm ramped up. I traveled near and below treeline across almost every aspect in the Mammoth area to see the effects of heavy snowfall and wind loading midday. I was not disappointed.

• Storm instabilities: wind slabs, storm slabs, and dry sluffs, were easy to trigger on test slopes on just about every aspect. Cornices from yesterday and this morning were touchy – very easy to trigger. Everything I triggered broke at the new/old snow interface. Slides ran fast and far, entraining a lot of soft new snow.
• It was snowing more than 2 inches per hour. It snowed 6 inches in 2 hours while I was out. The new snow was dry, despite temps rising slightly from just below, to just above freezing midday. I could tell it was warm before getting out my thermometer. Despite the dry nature of the new snow, I was getting soaked in my gore-tex. The sheer intensity of snowfall made the new snow settle fast and I was getting lots of cracking around my skis in flat terrain later in my tour.
• Strong to extreme southwest winds were loading leeward terrain features near treeline and limiting visibility.
• As I drove up from Bishop in the morning, the rain/snow line was at 6400 feet. On the drive down around 1 pm it had risen to 6900 feet. I saw some large rollerballs and a few small wet loose sluffs on the side of the road below 7000 feet where there was still snow cover.