Avalanche occurred as a result of Dec 26-27 storm event that produced 19" of snow at 2.6" SWE. Other avalanches in the area are assumed to have failure on a known persistent weak layer of facets 30-40 cms above the ground that formed during the November high pressure. No crown is visible from this avalanche and due to the long running nature it may be a storm snow soft slab avalanche. Avalanche detailed is labeled C.