A rare atmospheric river is hitting a large portion of the Midwestern and Southern U.S. this week, causing significant floods.

When a bomb cyclone meets an atmospheric river, the result is like an out-of-control fire hose A powerful storm hitting the West Coast combines these weather phenomena for a wet week in many areas.

Here's an explanation of how they form, their size and potential impacts. WHAT IS AN ATMOSPHERIC RIVER? The weather system occurs all over the world. It starts when a large amount of water vapor ...