Southern San Juan
SnowpackChris Bilbrey · Apr 1, 2021 · Southern San Juan
Weather
Warm and sunny. The light breeze at upper elevations was pleasant and took the edge off afternoon temperatures. Snow surfaces softened on E-S-W facing slopes up to 12,000 feet while northeast slopes held on to a thin zipper crust at the same elevation.
Snowpack
Below about 10,000 feet, the snowpack on all aspects was moist to wet throughout and becoming more rotten. Northerly-facing slopes above that and up to treeline only got moist on the surface with drier snow immediately below. We observed surface warming on east through south to west-facing slopes up to around 12,000 feet. Northeast-facing slopes in the alpine started to soften, but still held onto a thin yet breakable zipper crust. Only the top 4 to 6 inches of snow on sunny slopes got soft and is resting above a firm crust. The crust was thicker and harder to punch through the higher we climbed in elevation. However, this provided the right combination of wet snow and a slippery sliding surface to elevate the likelihood to trigger long-running loose wet slide on steeper slopes near treeline in the afternoon. At lower elevations, the buried crust was slightly softer and we did not observe the same sensitivity in wet snow on the surface. A snowpit on an east-facing slopes at 11,150 feet showed several concerning, softer snow layers that once lubricated by free water will be susceptible to failing as a wet slab. Compression and Extended Column Test produced clean, propagating failures in faceted snow in the top 70+ cm's. These are the same weak layers that were reactive in March, but at that time, in a dry persistent weak layer state. Now that liquid water is being introduced into these layers, it will be important to evaluate their failure potential during the current warming period.