Southern San Juan

Avalanche

Chris Bilbrey · Mar 19, 2020 · Southern San Juan

View on map

Weather

There's an old saying "making up for lost time". Well, the La Plata Mountains did just that. We found around 16 inches of new snow in the valley bottom at 9,000 feet. As we climbed higher in elevation, snow depths continued to increase and we found up to 30 inches of new snow around 11,000 feet. A high precipitation intensity moment observed between 10:00-11:30 am then on and off snowfall occurred for the remainder of the day (S-1 to S2+) with a couple more inches of accumulations. Skies were mostly obscured with very brief periods where skies broke just enough for the sun to poke through but never improve long-distance visibility.

Snowpack

New snow easily sluffed on treed slopes around 35 degrees and on the backside of steep rollovers. Sluffs were slow moving but did entrain a lot of snow while moving downhill. With the storm arriving warm to start, dense new snow bonded well to the pre-storm interface in below treeline terrain where we traveled. Walking along an exposed ridge top, the top 6 to 8 inches broke apart as soft slab but didn't travel far or propagate outward. This was mostly in deeper wind-drifted pockets. A snowpit on an east-northeast aspect just above 11,000 feet didn't yield propagating results in our Extended Column Test. However, large and moist facets (2 to 3 mm) linger under February snowfall about 1 meter below the snow surface. Triggering a slide in this layer would be large and difficult to survive. We felt that at higher elevations where weaker snow persist in a reactive state longer, we'd observe more troubling test results in buried weak layers. Sluff management was an important part of our travel protocols today and I'd anticipate more of the same tomorrow.

Avalanche

A group of riders reported triggering two slides in the northern half of the range. The group was unwilling to share exact location and details with forecast staff. One of the slides carried a rider for a short distance, didn't knock them off their sled, and debris piled up to their knees. They also reported two natural slides that crossed the main road after they passed under in the morning. The group was also unable to provide details but sounds like the avalanches were located north of Boren Creek and most likely originated off Babcock and Diorite Peaks.