Northern San Juan
AvalancheAnn Mellick · Dec 15, 2020 · Northern San Juan
Weather
Some persistent cloudiness to start, turning to mostly sunny skies by the afternoon hours. Very cold with a steady north wind, transporting lots of snow near and above treeline.
Snowpack
New snow since Dec 11th has added roughly 15"-25" to the overall height of snow, with much deeper drifts in wind loaded areas. This snow remains perched on a variety of snow surfaces, most notably the old weak near surface facets on shady slopes and firm crusts on sunny slopes. A new layer of near surface facets is forming at this interface on sunny slopes (just above the crust. This interface is not active yet, but will likely become more of a player in the future. Breaks between the series of three storms allowed for incremental loading and avoided a larger avalanche cycle due to slower loading. However, the last storm (Dec 14-16) tipped the scales and we saw the biggest cycle of the season. Widespread cracking and collapsing in flats and on shadier slopes below treeline. Slopes near and above treeline quite wind afected and slabby.
Avalanche
Evidence of lots of slide activity from past 24 hours. Seems as though there was a cycle on northerly aspects near/above treeline associated with the strong southerly winds on Dec 14th. These slides are snow covered from the storm on the 15th and a little harder to discern. Then another cycle from the new snow load on the 15th. This was more widepread with slides on a variety of aspects and elevations. Slides remain on the small side, but volume and propagation continue to increase.