Professional Observation

Observation Details

Signs of Unstable Snow

Key Points

We traveled on near and below treeline terrain below 9000 feet looking for solar warming and trying to get a clearer picture of weak layers buried on the 29th and the 19th.

• We found both persistent weak layers (20 to 40 cm below the surface, and 70 to 80 cm below the surface respectively) on north, northeast, and east aspects. Both consisted of small facets above melt-freeze crusts. We got sudden planar and sudden collapse results in compression tests but no propagation in multiple long-column tests. This shows the tricky nature of our current persistent slab problem because 3 miles away from us in V Bowl a slab avalanche released on an east-northeast aspect at 9000 feet at 2 pm today.
• The avalanche ran over the skin track of 2 nearby skiers that watched and felt it release. No one was caught or carried in the slide. The reporting party told me they saw no previous signs of instability. The crown boke across a convexity below treeline ~150 feet wide (measured using mapping software). The skiers reported conducting hand pits and felt no crust shallower than the bed surface (~1-2.5 feet deep) of the avalanche – which they said was a melt-freeze crust. Because the skiers were close to the crown when it broke and they felt it release we suspect it was remotely triggered. Because the bed surface was the upper-most melt-freeze crust in the snowpack we suspect it ran on the thin layer of facets atop the crust buried on 3/29. See avalanche observation for more details.
• Some wet loose avalanches had run on solar aspects yesterday and we saw some small new ones that ran today. We found some hints of warming on northeast-facing slopes below treeline and also saw some new rollerballs in steep northeast chutes today.
• We did not travel above treeline where winds on the Dana Plateau were out-performing the forecast and drifting snow into the tops of alpine chutes for long periods of the day.