You may have heard the term atmospheric river used over the past couple of days. Especially with the ongoing storms in parts of California. So, what is an atmospheric river and why can it cause so many problems?

An atmospheric river is a region of very moist air from the tropics that is transported to mid-latitude areas. You may have heard it described as a firehose of moisture in the atmosphere. It is very similar to a firehose in the fact that there is a lot of moisture being transported to an area.

It begins over the ocean with winds pushing tropical moisture toward land. When the winds become stronger, narrow bands of extremely high moisture develop called atmospheric rivers. These bands are then transported by atmospheric winds towards areas of land.

Along coastlines, the atmospheric river produces narrow bands of heavy rainfall. A little further inland, mountains lift the atmospheric river in a process called orographic lifting. This results in even heavier rainfall and snow in higher elevations.

Some atmospheric rivers even have regional names. The rain and the snow that has been occurring in parts of California is due in part to an atmospheric river called the Pineapple Express. This type of system that brings a lot of moisture to the area can result in flooding and even landslides.