Quick report
Weather station data suggested new snow in the Mammoth area was denser than areas to the north and south (10-12% vs. 6-8% density). Judging by the heavily-rimed snow, the San Joaquin River drainage must have released some convective instability as it converged storm air over the mountains, causing the density discrepancy. New snow was soft and readily available for transport in the trees. If the winds had been sustained, there probably would have been wind drifts, even below treeline. It wasn’t; wind drifts were very small and isolated. Surface wind effects were subtle. I did not see signs of instability where I travelled below treeline. Very soft storm slabs were weak but showed no signs of propagating. If significant wind were added to the picture, I would have been worried!
Weather
- Air Temp
- 23F @2:45pm
- Cloud Cover
- broken
- Wind Loading
- moderate
- Rain Elevation
- N/A
- Recent Snowfall
- 22-25cm
- Snow Avail For Transport
- moderate amounts
Despite some sunshine in town, it was still a storm day in the mountains with wind and snowfall intensifying into the afternoon. At the beginning of my tour around 1230 pm, occasional holes in the clouds allowed some sunshine to sneak in. Visibility was good at low elevations while mountain clouds obscured the Crest. Snowfall was intermittent, very light graupel with trace accumulation. Winds were generally calm in the trees but with occasional gusts to moderate. Around 2:30pm, snowfall increased and visibility decreased. Precipitation rates increased to 2cm/minute becoming lightly-rimed dendrites. Winds continued to be gusty, but increased in intensity and duration, coming from a generally SW direction. Periods of moderate blowing snow pushed snow up the west side of Sherwin Ridge and across the road.
Snowpack
New snow was heavily rimed, depth approximately 22-25cm sitting on top of a crust from the warm temps this week. Snow was soft in the trees but had some cohesion, making very soft storm slabs. Slabs were weakly-formed and showed a high propensity to break but not propagate. No shooting cracks, just breaking into soft chunks at your feet. Hand shears readily pulled snow out in blocks at an interface within the new snow about 15cm down and at the old surface crust. Pit tests showed easy, resistant planar and non-propagating results. Further investigation showed the storm snow interface occurred where lightly-rimed stellars and columns became heavily-rimed precipitation particles without their previously well-defined forms. I dug two snow pits in the same area but different aspects (WSW and WNW), snow height 143-149cm. The new-old interface was a roughly-textured melt freeze crust. I could not find any near surface facets or weak grains between the crust and new snow. The snow below the crust was moist becoming wet as deep as I dug (for another 40-50cm) with a couple more crusts mixed in. What was different? WSW pit: The crust at the new-old interface was very robust and knife-hard. Below it, the snow was 1F+ large melt forms with another pencil-hard crust mixed in. WNW pit: Crusts were softer and more decomposed. The layers in-between started as large melt form polycrystals, but quickly became pencil-hard wet small rounds.