Severe Storms/Atmospheric Rivers

This page is to be used for the Severe Storms topic of the Meteorology event.

Atmospheric Rivers
Atmospheric rivers are narrow bands of enhanced water vapor transport. They are often found in the warm sectors of mid-latitude cyclones that form over water. The warm sector can also entrain moisture from oceanic regions. These are relatively long, narrow regions in the atmosphere, almost like a river in the sky, that transport most of the water vapor outside of the tropics.

Characteristics of Atmospheric Rivers
Atmospheric rivers (ARs) are narrow, usually only about 100 kilometers wide, move quickly, about 85 kilometers per hour at the core, and are centered about one kilometer above the surface. ARs are responsible for almost all (>90%) of the global north-south transport of water vapor. Some ARs carry up to 50,000,000 liters of water per second.

Impact
Atmospheric rivers are largely responsible for incidences of extreme precipitation in the west coast regions of the middle latitudes (e.g., the West Coast of North America, western Europe, and western North Africa). These incidences of extreme precipitation result in severe flooding.

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 can:
 * Disrupt travel
 * Induce mudslides
 * Cause catastrophic damage to life and property

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.

Precipitation from ARs likely caused the Great Flood of 1862. The USGS has developed a theoretical scenario called ARkStorm in which an AR causes extreme flooding in much of California.

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 water supply and flood risks, especially the western region of the U.S.

Pineapple Express
A strong atmospheric river that is capable of bringing moisture from the tropics near Hawaii over to the U.S. West Coast.

Research and analysis
NOAA 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.



More Information

NOAA

Wikipedia

How Atmospheric Rivers Form