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Atmospheric Rivers
What are
atmospheric rivers?
National Oceanic
& Atmospheric Administration
Learn more about these rivers in the sky
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.
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 (e.g., NOAA
Hydrometeorological Testbed and CalWater) 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.
Scientific research yields important data
that helps NOAA's National Weather Service forecasters
issue warnings for potential heavy rain and flooding in areas prone to the
impacts of atmospheric rivers as many as five to seven days in advance.
To learn more about atmospheric rivers,
please visit: http://www.esrl.noaa.gov/psd/atmrivers/.
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is an agency that enriches life through science. Our reach goes from the
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public informed of the changing environment around them.
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