Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

I got out for a short tour to test wind slabs near treeline in the northern half of the forecast area.

• I intentionally triggered a few small wind slab avalanches, shooting cracks, and small cornices on north and northeast-facing test slopes at the summit. Other east and southeast-facing slopes were stubborn. North winds just began stripping northerly slopes as I headed down around 1pm. Before that time, south and west aspects were stripped or sheltered from the wind. No wind slabs on those aspects.
• No sluff or storm slab instabilities in sheltered terrain below treeline. I dug a test pit to look at the upper snowpack. (See shovel tilt test photo.) I did not find persistent weak grains in the upper pack or under the new snow except near the summit on a south-facing slope where I saw small near-surface facets forming above and below a sun crust at the surface. It was easy to tell sheltered terrain not just because of the snow still in the trees and lack of wind, but because there where big beautiful stellar dendrites (that’s geek for snowflakes) on the surface. With cold high pressure in the forecast, there’s a lot of low density snow to facet at the surface. I consistently found temperature gradients in the top 20cm more than strong enough to drive that process.
• The storm moved from north to south across the mountains. On my drive up from Bishop it was mostly clear with little blowing snow until Mammoth. From Mammoth north is was snowing lightly (S-1) and there was moderate to intense blowing snow at all elevations down to the side of 395. On my drive back in the afternoon, it was clearing as I headed south to Mammoth. Then it was snowing and I saw blowing snow at all elevations south into Bishop Creek.