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In 2019, meteorologists nationwide began rating atmospheric rivers (AR), storms that have the potential for millions of dollars in losses and severe flooding. However, what exactly is an atmospheric river? It’s a long, narrow river of condensed water vapor in the atmosphere that moves with the weather. A strong river can carry between 7.5 -25 times the flow of water that passes through the mouth of the Mississippi River. These rivers in the sky can be 300 miles wide, a mile deep and more than 1,000 miles long. Most are small, but they can be massive and fast moving, and when the storms make landfall, they often release rain or snow, sometimes in large amounts. They account for 50 percent of the annual precipitation in California, and are the West Coast’s big storms, and are responsible for 65 percent of the western USA’s extreme rain and snow events. The storms develop in the tropics and are also known as the Pineapple Express. They are a default feature of the entire global water cycle, and are present somewhere on the planet at any given time.

While most atmospheric rivers are small and beneficial, providing rain and snow to the western states, the massive atmospheric rivers can cause significant flooding. As identification and prediction of atmospheric rivers has improved, the scale was developed to let people know what to expect and how to prepare if the storm is going to be strong. Similar to hurricanes atmospheric rivers are ranked 1-5. The ranking uses Integrated Water Vapor Transport (IVT), which is the amount of water vapor in the system and the wind moving it around, and the duration of the storm.

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