Southern San Juan

Avalanche

Chris Bilbrey · Dec 18, 2020 · Southern San Juan

Weather

Clouds moved in and out for most of the day. Winds were calm with periods of a light breeze in the alpine.

Snowpack

Molas and Coal Bank study plots measured 8 inches of snow this morning. We found 5 to 7 inches at 11,000 feet a few hours later. Low-density snow was quickly settling with periods of sun. Below treeline, storm snow fell onto a firm crust on east through south aspects and above prior storm snow on northerlies. As we approached 11,300 feet, we began to observe numerous rumbling collapses on north through east aspects. A snowpit at 11,500 feet yielded propagating results (ECTP 15) failing in the thick layer of facets sitting below December snowfall. As we crested treeline, we found many slopes with a hard wind-stiffened layer below recent snowfall. This hard layer develop from Tuesday's strong north-northwest winds. New snow resting on top was bonding well and only producing small cracking on steeper slopes and in thicker drifts. Fresh drifts in the alpine were 16 to 24 inches thick. Wind-sheltered areas in the alpine and near treeline are where we experienced the most widespread collapsing. These locations are where the December slab is the deepest above a layer of facets and where it seems easier for a rider to impact weaker snow below. Snow depth on southeast-facing slopes continues to get deeper with each storm cycle. We found about 8 inches of storm snow sitting above a crust with near-surface facets above and below the crust. At present, this load does not appear to be enough to tip the scale on the crust/ facet combo in this area, but something to watch out for with subsequent loading periods.

Avalanche

Lots of small, loose snow sluffing on east and southeast-facing slopes in alpine from morning sun. They mostly originated out of steep, rocky terrain and none traveled far or grew large enough to be classified as a size 2.