Natural avalanche overnight

Start was purple knob. Overnight early Jan 2nd. Completely natural. Observed the start zone on leeward side of purple knob. It ran down the open side path but stopped before trees . Approximately 2/3 way down the path. It was all surface and nothing propogated. I skied this slope Jan 1st and again Jam2nd. It was not there when I left at 4pm near dark on Jan1st and surprised to see it with fresh 5 cm of snow on it this morning.