Atmospheric rivers are narrow bands of intense water vapor transport that can form over the ocean and direct massive amounts of water towards the land. The results of this high-density flow of water are precipitation events which drop very large amounts of rain in a short time period, leading to flooding, landslides, and other extreme events. You can read more about atmospheric rivers at https://gardenprofessors.com/cry-me-a-river/. We used to think that atmospheric rivers were mostly confined to the west coast of the United States, but more recent studies have shown that they can occur in many parts of the world, including the Southeast. Recent research has indicated that the average position of atmospheric rivers is shifting to the north, bringing heavy rains to region that have never experienced these high-intensity storms before. You can read more in The Conversation here.