Southern San Juan

Avalanche

Chris Bilbrey · Dec 28, 2021 · Southern San Juan

Weather

Snowed all day. Mostly S2 with periods of S5. New snow ranged from 8 to 10 inches below 10,000 feet, and up to 2 feet by the time we hit treeline. Winds were light along ridgetops and in the alpine. Plenty of snow and rime still in trees at treeline suggesting little wind transport during heavy precipitation periods.

Snowpack

Snow depths in the southwest corner of the range have increased exponentially during December creating an overall supportable snowpack. Below 11,000 feet, most aspects have a uniform, right-side-up snowpack void of old November snow. A few thin, crust exist on east-facing slopes but were unreactive in our snowpits. We found weaker facets at the ground on northerly-facing slopes above 11,000 feet, but those grains are now buried around a meter or deeper. No cracking or collapsing observed on northerly-facing slopes or along ridgetops. While triggering an avalanche in deeper weak facets on the surface might appear less likely, the consequences of doing so are much bigger with a 3 to 4 foot slab above. All it takes is finding a shallower part of the slope where a rider can more effectively impact weak snow below. On east-facing slopes at upper elevations, a faceted crust looms that formed between December 12 and 13. This interface was stubborn to fail in snowpack test. The most recent snowfall was low density with little evidence of wind-drifting. With a plethora of cold-smoke snow on the surface, an increase in winds will easily build stiffer slabs at upper elevations over softer snow layers, and potentially increase the likelihood to trigger a larger avalanche.

Avalanche

Evidence of a large crown on an east aspect of Madden Peak that most likely ran sometime around the 24th or 25th. Crown mostly filled in and directly below the ridgeline south of the summit.