Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

We found reactive wind slabs breaking within the new snow, at the new/old interface, and on weak facets in the Lee Vining area today.

• Wind slabs were isolated in very exposed terrain below treeline – we triggered one on a cross-loaded, southeast-facing slope on the moraine. On the northeast aspect of a ridge near treeline at 9800 feet we intentionally triggered about 10 soft wind slabs and a few sluffs. Our longest and deepest shooting cracks broke down through a facet layer buried under the new snow. We also got minor sluffing in the storm snow in wind-sheltered terrain.
• Below 9500 feet we found about 4-8 inches of new low-density (F) snow. On solar aspects this sat atop a thin melt-freeze crust with well-developed facets under the crust. On wind-exposed terrain the new snow sat on old hard windboard. In the shelter of trees, the new snow sat right on top of a layer of facets.
• Above 9500 feet we found 10-12 inches of new snow sitting on the snow from 1/29-1/30, old wind slabs, or atop the facet layer.
• In exposed terrain and at higher elevations than we ventured, extreme west and southwest winds where blowing snow all day across the whole range. Snow showers were fickle. There were a few short breaks in snowfall and periods of heavy (S5) precipitation. Ligth to moderate snowfall (S1-S2) was most common. The storm seemed to stall out at about 8500 feet and the Mono Basin and 395 corridor were sunny in the afternoon.

We stuck to low slope angles and sheltered terrain with no overhead hazards.