Atmospheric rivers are a natural and important part of weather around the world. But just what is an atmospheric river and what does it mean when one is on its way?

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Imagine long, skinny "rivers" way up in the sky, but instead of liquid water, they are made of water vapour, like steam.

These are atmospheric rivers.
And they are a natural and important part of our planet’s water cycle, providing fresh water for plants, animals and people around the world.

As the sun heats the earth, the warm temperatures near the tropics and subtropics cause large amounts of water from the ocean to evaporate, becoming water vapour, which rises into the sky.

Some of this vapour can pull away, forming long “rivers” of moisture in the atmosphere.

When an atmospheric river reaches land, the cooler air causes the water vapour to turn into rain or snow. This brings much-needed water to many places around the world.

There are atmospheric rivers around the world every day. And most aren’t a problem. But when large, long lasting ones form, they can drop a month’s worth of rain or snow, in just a few days.

Usually, much of the water soaks into the ground. But if the ground is already very wet, or forest fires have burned away the soil’s ability to hold lots of water, then some atmospheric rivers can bring more water
than our cities, roads and ecosystems can handle: causing floods, and triggering landslides.

Meteorologists watch these "rivers" closely, and use information from weather stations, radars, satellites, and more (visual includes: ships, planes), along with very powerful supercomputers, to predict when they’ll arrive, and how much water they’ll bring.

Because of climate change, weather patterns are changing. And these changes mean large, long lasting, atmospheric rivers can stay in one place longer.

And warmer air can hold more moisture. So as the atmosphere warms, atmospheric rivers are able to carry even more water. And when they reach land, drop even more rain or snow.

But you and I, we can be ready.
We can keep emergency supplies at home, in case we need them.
And we can pay attention to weather forecasts, so we know when lots of rain or snow is coming our way.