Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapor outside of the tropics. These columns of vapor move with the weather, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow- and usually a lot of it! A series of atmospheric rivers brought drought-relieving rains, heavy snowfall and flooding to California this week is highlighted below as well in a new movie created with satellite data from the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite. The images were collected between January 7-11th. They show the amount of moisture present in the atmosphere and its movement across the Pacific Ocean to the United States, where much of it fell as rain or snow. Watch it here.
In early January 2017, the west coast experienced rain and flooding from a series of storms flowing from America on multiple streams of moist air, each individually known as an atmospheric river.
Check out this loop of a recent atmospheric river that has wrecked havoc on the California coast below:
Video Courtesy: NWS Ocean Prediction Center
Although atmospheric rivers come in many shapes and sizes, those that contain the largest amounts of water vapor and the strongest winds can create extreme rainfall and floods, often by stalling over watersheds vulnerable to flooding. These events can disrupt travel, induce mudslides and cause catastrophic damage to life and property. A well-known example is the "Pineapple Express," a strong atmospheric river that is capable of bringing moisture from the tropics near Hawaii over to the U.S. West Coast.
Not all atmospheric rivers cause damage; most are weak systems that often provide beneficial rain or snow that is crucial to the water supply. Atmospheric rivers are a key feature in the global water cycle and are closely tied to both water supply and flood risks — particularly in the western United States.
While atmospheric rivers are responsible for great quantities of rain that can produce flooding, they also contribute to beneficial increases in snowpack. A series of atmospheric rivers fueled the strong winter storms that battered the U.S. West Coast from western Washington to southern California from Dec. 10–22, 2010, producing 11 to 25 inches of rain in certain areas. These rivers also contributed to the snowpack in the Sierras, which received 75 percent of its annual snow by Dec. 22, the first full day of winter.
NOAA research uses satellite, radar, aircraft and other observations, as well as major numerical weather model improvements, to better understand atmospheric rivers and their importance to both weather and climate.