Northern San Juan

Avalanche

Bill Nalli · Dec 28, 2019 · Northern San Juan

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Weather

Intermittent snowfall throughout the day added about 4 inches new in non wind affected areas. Winds shifted to the NW after noon and began drifting snow below ridges and across terrain features. Colder air moved in after 2 pm. Poor visibility all day.

Snowpack

Areas below treeline and out of the wind are generally stable with nice right side up new snow. Average 18 to 24 inches of new settled snow. The upper 6 inches is blower powder. This made for excellent skiing. While the wind during the storm was mostly behaved, areas below ridges and exposed terrain features have new sensitive wind drifts. These are the locations where riders can trigger avalanches. I found one NE test slope where I could trigger a very small slab indicating this sensitivity. Visibility was poor but no signs of deep avalanches near the ground were seen. Many L-N-D1.5's were seen in steep terrain greater than 40 degrees. Most stopped at the first slope angle transition. The layer of greatest concern is currently the new/old snow interface prior to Dec. 24. Small faceted grains here are active in stability tests and are also the likely failure layer in one skier triggered slide from early today.

Avalanche

We came upon this recent skier triggered avalanche at about 3pm. It was on a NW aspect at 11,600 feet. From the ridgeline we could see one track going into the slide near the apex of the crown. No tracks exited the slide back to the ridgeline and we could not see any other evidence in the chute below. After much deliberation amongst our group we decided not to search further. There was about 4 to 6 inches of new snow on the bed surface and the entrance track. We estimated it was triggered very early in the morning and a rescue effort more than seven hours later would not be worth the risk to our group. There was still more snow on the flanks of this slide that didn't slide and other steep suspect slopes to navigate once in the drainage. We truly hope this incident ended with a good outcome.