The term “atmospheric river” is relatively new in the science of meteorology. An article in Geophysical Research Letters in 1994 by Yong Zhu and Reginald Newell defined the term because some of these “filaments” of water vapor “carry as much water as the Amazon.” Essentially, these are plumes of water vapor in the atmosphere which originate over the ocean and when coupled with a storm system, can cause massive amounts of rain and snow.
Areas in California received flooding rains in the past two weeks, and much more is expected in the coming several days. The map below shows expected rain and snow between now and Saturday afternoon. Some areas will get as much as 10 inches of rain, while mountainous areas could see 2-3 feet of snow.