"Atmospheric rivers, or ARs, are described as “narrow regions of intense moisture flows in the lower troposphere of the atmosphere that deliver sustained and heavy rainfall to mid-latitude regions.”
"They can be up to 300 kilometres wide and up to 2,000 kilometres long. They flow, invisibly, about one to 2.5 kilometres above the surface of the ocean. There can be multiple atmospheric rivers at any time covering the hemisphere.
"Known to bring heavy rainfall, they have been blamed for severe flooding in California and in England."
Full article: Derecho, atmospheric river: new weather terms demystified.
