Southern San Juan

Avalanche

Chris Bilbrey · Feb 4, 2021 · Southern San Juan

Weather

Sunny but cool day with moderate westerly winds and strong gust along ridge tops. There was only a skiff of new snow in the valley bottom and around 2 inches above 10,500 feet. Drifts were only 4 or 5 inches deep and isolated. This last system provided more wind than snow and also...a thin layer of dust on the surface.

Snowpack

We found shallow but stubborn wind-drifted slabs near treeline and in protected alpine areas. This area received more wind than snow overnight and the winds easily moved and shuffled the new snow into either very firm wind-board or 4F to 1F slabs. Fresh slabs were unreactive to ski pressure on small, non-consequential slopes and stability test evaluating their sensitivity was inconclusive - most did not propagate in test but a few did. Propagating results was more consistent where fresh slabs formed above a firm melt-freeze crust from recent warm temperatures. Digging deeper revealed lingering facets and depth hoar below snowfall from January. The overlying slab is around 50 to 70 cm's thick depending on location and aspect. Compression test produced planar failures with around 12 taps and Extended Column Test consistently failed with 21 taps in 4 to 6 mm facets/ depth hoar. Two snowpits were performed above old crown's (East and Southeast) from multiple large avalanches that ran around 1/26. Moving forward, places where the full snowpack remains could be a more difficult area to trigger a slide and areas that already slid are setting up to be repeat offenders as the overlying slab thickens above the same weak layer that didn't get flushed down the slope. Recent warm temperatures left a thin, zipper melt-freeze crust on northerly-facing terrain below treeline with a much thicker and harder crust on east to south through west aspects.

Avalanche

No new avalanches observed.