Southern San Juan
AvalancheNoah Sievers · Jan 24, 2021 · Southern San Juan
Weather
Heavy snow, ranging from 1-3mm in size started falling around 1800 MST on 1/22 at Wolf Creek Pass. Southwest winds picked up to 20-30mph with 40mph gusts overnight. By 0800 MST on 1/23, snow accumulation had reached 10 inches in sheltered, near-treeline elevations (approx. 11,000 ft), and visibility was minimal. Stronger winds and heavy snow continued throughout day, and by 1200 MST; southwest winds were reaching 25mph with 45mph gusts. By 1330 MST, recent snowfall accumulation was approx. 15 inches, which had been undergoing heavy transport by SW winds to leeward slopes (NE to SE aspects). Visibility continued to be minimal in afternoon hours, and at times of strong gusts; it was blizzard-like. All snow crystals that had started falling in the previous night (1/22) into Saturday (1/23), were consistently identified as graupel. Temperatures during storm were consistently 10-16 degrees F. Nimbostratus cloud coverage was continuously OVC, and sunlight did not penetrate the area for over 24 hours.
Snowpack
Small SE to E aspect terrain features had quickly formed stiff wind-affected slabs from the occurring snowfall and heavy winds. Sounds of localized whoomphing were noticed near treeline on SE aspects, as the new snow load had became unsupportable over the course of the storm/day. N and NE aspects were sheltered and relatively stable during mornings hours, but stability quickly diminished as the new snow load increased on the weaker near-surface layers. This load created a noticeable soft storm slab on N and NE aspects. New now was on the heavier side, but dry enough for minimal snow crystal cohesion during the day. Conditions became more touchy as the day progressed for all mountain aspects in the Lobo Overlook area.
Avalanche
A skier-triggered avalanche occurred on a SE facing, roughly 32 degree corniced developed slope at 11,049ft; at approx. 1334 MST. Slope was attached to a large, steep gully overhead. The lower gully wall feature propagated and released when skier made first turn near concave slope. The avalanche consisted of a hard packed slab with a 6-15 inch crown. It ran for roughly 60 feet in width, and 25 feet in length. The slab likely failed on the weak foundation from the near-surface crust. The propagation occurred within the small terrain feature, but did not extend uphill into the SE facing gully. Skier was not caught, and was able to ski out of debris path and self rescue from avalanche terrain. A second avalanche occurred directly after the skier-triggered avalanche. It was considered a remote-triggered avalanche. This slide occurred directly after the skier-triggered avalanche, on a SE facing, roughly 30 degree wind-loaded slope at 11,040ft. Remote-triggered avalanche occurred in a small gully wall directly adjacent to the skier-triggered avalanche, likely from the groups weight and cautious movement above slope when exiting area. The avalanche propagated along a similar path/route as the skier-triggered avalanche, and the crown varied between 3-10 inches in height. This avalanche ran roughly 40 feet in width, and 20 feet in length. Both avalanches shared similar releases, with minimal energy needed to produce failures in the near-surface snowpack layers.