Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

I went to the Lakes Basin to take a look at buried persistent weak layers where the snowpack is deepest.

• I found the December 1st persistent weak layer buried an average of 110 cm below the surface. I did a propagation saw test near where another forecaster did one on the 15th and got very different results. I had to cut my column almost all the way to the end before the fracture propagated. (See attached profiles)
• The snowpack has been settling a few inches each day. We found settlement cones around trees. We found that our skis and feet didn’t sink very far into the snow and that the snowpack in general is getting denser.
• It was breezy above treeline near the Mammoth Crest but we saw no blowing snow and no new wind slab formation. Wind-affected surfaces invaded even sheltered areas because of strong winds earlier this week. Old wind slabs were impervious to our stomping. Surface hoar and near-surface facets atop those wind crusts clued us in that it had been cold and calm at night.
• It was warm in the sun. We found moist, spring-like snow (melt forms) on south and southeast aspects. We saw no rollerballs or loose wet avalanches.

While we found a deep, uniform, and relatively strong snowpack near and below treeline, probing around at about 10,400 feet showed us just how variable snow depths are on the Crest. We avoided that terrain and found boot-top recycled powder skiing in the trees.