Atmospheric rivers are corridors of concentrated moisture in the atmosphere that can span hundreds to thousands of kilometers. These “rivers in the sky” typically occur along the boundaries between warm and cold air masses and transport large amounts of water vapor from tropical or subtropical regions into higher latitudes.
An atmospheric river is a narrow corridor or filament of concentrated moisture in the lower atmosphere. These rivers, which can be hundreds to thousands of kilometers long and a few kilometers to tens of kilometers wide, are responsible for most of the horizontal transport of water vapor outside the tropics. Atmospheric rivers typically follow paths along either side of the subtropical ridge—the area of highest atmospheric pressure in the world located roughly between 30° and 35° latitude—and they can be particularly strong and persistent over the Pacific Ocean where they are often referred to as “Pineapple Express” systems.
In North America, an atmospheric river is also sometimes called a “North Pacific storm.” While they occur year-round, atmospheric rivers are most common in winter when the contrast between air temperatures is greatest. In general, stronger temperature gradients produce more powerful weather systems.
When these weather systems move over warm ocean waters, they can pick up vast amounts of water vapor—as much as 10 times more than average precipitation rates—and carry it inland where it can fall as rain or snow.
Atmospheric River Oregon
An atmospheric river is a long, narrow region of enhanced water vapor transport in the atmosphere. These rivers form along weather fronts and can stretch for thousands of kilometers. They are responsible for most of the horizontal transport of water vapor outside of the tropics and play an important role in the global water cycle.
Atmospheric rivers typically deliver high amounts of precipitation, often leading to flooding. The term “atmospheric river” was first coined in a paper published in 1982 by liquid water meteorologist Martin Trenberth and colleagues. It has since become widely used by the scientific community.
While atmospheric rivers can occur anywhere in the world, they are most commonly associated with the West Coast of North America. This is due to the unique topography of the region, which allows for moist air from over the Pacific Ocean to be funneled inland during storms. Atmospheric rivers have been shown to play a significant role in California’s hydrology and have been linked to both drought and flood conditions in the state.
In recent years, Oregon has also experienced several major floods that have been attributed to atmospheric rivers. In 2012, an atmospheric river known as “The Perfect Storm” caused widespread damage across Oregon and Northern California. This event resulted in over $1 billion in damages and led to nine deaths.
More recently, another strong storm system brought heavy rains and high winds to Oregon in early 2017 causing widespread power outages and flooding across much of the state.
While they can cause serious problems, it’s important to remember that atmospheric rivers also play an important role in our planet’s climate system.
Credit: www.wweek.com
Why is It Called an Atmospheric River Now?
An atmospheric river is a narrow, intense band of moisture in the atmosphere that transports water vapor around the globe. These “rivers” can be up to a thousand kilometers wide and can carry as much water vapor as the Mississippi River discharges into the Gulf of Mexico.
The term “atmospheric river” was coined in the 1990s by researchers who were studying how water vapor is transported around the world.
They noticed that most of the world’s precipitation comes from just a few very narrow bands of moisture in the atmosphere, which they likened to rivers.
While initially used only by scientists, the term “atmospheric river” has become more widely used in recent years as our understanding of these features has grown. Nowadays, you’ll hear it used both by scientists and laypeople alike when referring to these powerful bands of moisture.
What is an Atmospheric River Portland?
An atmospheric river is a large band of water vapor in the atmosphere that transports huge amounts of water from one place to another. The Portland area is particularly vulnerable to these events because it lies in the path of two major storm tracks, the Pacific Northwest and the Aleutian Low. When an atmospheric river hits Portland, it can bring heavy rains, strong winds, and high waves.
These events can cause flooding, mudslides, and power outages.
How Often Does Atmospheric River Happen?
Atmospheric rivers are aptly named for their striking resemblance to terrestrial rivers. They are relatively long, narrow bands of enhanced water vapor transport typically found in the tropics and subtropics. Atmospheric rivers typically extend from the Tropics into mid-latitudes and can deliver an enormous amount of moisture—the equivalent of 10–20% of the total annual flow of water in the Amazon River.
While they occupy only a small portion of the globe at any given time, atmospheric rivers can have a large impact when they make landfall. When an atmospheric river makes landfall, it can cause heavy rainfall and flooding, strong winds, and high waves. In fact, many of the most damaging floods in U.S. history have been associated with atmospheric rivers (ARs).
For example, ARs were responsible for causing more than half of California’s flood damage between 1950 and 2010 according to one study. Furthermore, about 75%2 of the so-called “Pineapple Express” storms that bring warm moist air from Hawaii northward to California during winter are associated with ARs. The frequency with which atmospheric rivers occur varies depending on location.
In general, areas closer to the equator experience more frequent atmospheric rivers than areas located further away from the equator. For example, research has shown that there are about 30–40 atmospheric rivers per year over tropical regions3 but only about 5–7 per year over North America.
How Rare is an Atmospheric River?
Atmospheric rivers are not as rare as one might think. In fact, they occur every day around the world, though most are relatively weak and do not last long. The term “atmospheric river” was first coined in the 1990s by researchers studying weather patterns in the Pacific Ocean.
These researchers noticed that certain weather systems – typically associated with warm, moist air flowing from the tropics – were responsible for a disproportionate amount of precipitation along the West Coast of North America. While atmospheric rivers can bring heavy rains (and sometimes snow), they are not always destructive. In fact, they can be beneficial, providing much-needed water to drought-stricken areas.
It is only when these weather systems stall over an area for an extended period of time that they become dangerous, causing flooding and other damage. According to the National Weather Service, there are four main types of atmospheric rivers: coastal, frontal, pineapple express, and subtropical. Coastal atmospheric rivers form along the west coasts of continents and are often associated with strong winds and high waves.
Frontal atmospheric rivers form along cold fronts and can cause significant amounts of rainfall over short periods of time. Pineapple expresses atmospheric rivers that form between Hawaii and California and is characterized by warm, moist air flowing from the tropics.
Atmospheric river hits Oregon leaving thousands without power
Conclusion
Atmospheric rivers are narrow corridors of concentrated moisture in the atmosphere. Also known as “Pineapple Express” systems, they can transport an amount of water vapor equivalent to 20-25% of the average flow of water at the mouth of the Mississippi River. These events can cause heavy rains, strong winds, and flooding.
The National Weather Service has issued a Flood Watch for portions of northwest Oregon from late Wednesday night through late Thursday night, as an Atmospheric River is expected to bring heavy rain and high winds to the area. The heaviest rain is expected to fall along the coast and in the Cascade foothills, with 5-8 inches possible in some areas. This could lead to widespread flooding and travel disruptions.
Residents should be prepared for power outages and possible road closures.
