Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

I went to look at surface conditions and the state of the persistent slab structure in the Mammoth Lakes Basin before the storm.

• I found an avalanche that broke on weak facets during the last storm. I did a crown profile and found the December 1st facet/crust combo alive and weak at the failure plane. I got sudden compression test results in the same layer.
• By aspect:
  • North to northeast aspects BTL/NTL have about 3 inches of soft, wind-blown snow above a stiffer, supportable layer. In more exposed terrain there’s a thin wind crust at the surface. HS = 80-140 cm.
  • Southeast and south aspects BTL/NTL had a 1 cm thick sun crust. Solar aspects ATL were stripped by the wind.
  • West and northwest aspects had variable snow depths because of cross-loading or stripping. The surface was a harder, 1 cm rimed wind crust. HS = 70-135.
• There was more blowing snow in the Mammoth Area than expected. The only wind slabs I found NTL were very small.

With variable snow depth and a weak snowpack structure, I rode slopes less than 30 degrees and found fun, surfy skiing on northerly slopes.