With all the heavy rain and flooding across our state this Winter, you may have seen the words "atmospheric river" come up on the news. But what really are atmospheric rivers? And what can you do to be prepared?
What is an atmospheric river?
Atmospheric rivers are massive currents of water vapor in the atmosphere that carry water from the warm, humid, tropic towards the cold poles. Because of this, some routes are nicknamed the "pineapple express".
Atmospheric rivers are large - they can carry water for thousands of miles. They often carry much more water than "normal" rivers on land!
How do they form?
Near the equator, there is lots of sun and lots of water (key elements of many famous tropical beaches!). The heat from the sun causes water to evaporate into the atmosphere (hello, humidity). This humid air rises to form a channel in the sky over 200 feet wide and soars away from the tropics, carried by wind towards the colder and less humid poles.
To understand why atmospheric rivers cause rain, remember that "warm air rises, cold air sinks". When an atmospheric river hits California, mountain ranges force the current of water vapor to travel higher, into colder temperatures. When the water vapor cools, it falls as rain or snow.
In California, almost half of all precipitation comes from atmospheric rivers. This can be from either heavy storms or mild rain showers.
What can you do to be prepared?
- Learn about your community's emergency plans, warning signals, evacuation routes and locations of emergency shelters.
- Inform local authorities about any special needs, i.e., elderly or bedridden people or anyone with a disability.
- Plan and practice a flood evacuation route with your family. Ask an out-of-state relative or friend to be the "family contact" in case your family is separated during a flood. Make sure everyone in your family has their contact information.
The California Department of Public Health website has Emergency Preparedness information for a variety of conditions including floods and power outages. Learn more here.