Found in the Yuan play 《渔樵记》 (attributed to 无名氏): '纷纷扬扬，下着如此这般大雪' — 'swirling thick, the snow came down like this.' The phrase has been the stock image for heavy, drifting snowfall since Yuan vernacular drama.
usage
Almost always used for things falling lightly through the air — snow (most common), leaves, petals, ash, paper scraps. Can also describe rumors/news spreading chaotically (消息纷纷扬扬). Structure 纷纷扬扬地 + V is very common.
