What is El Niño?
El Niño is part of a naturally occurring cycle of temperature fluctuations in the Pacific Ocean.
El Niño occurs when the water is warmer than average, and La Niña occurs when the water is cooler than average. El Niño happens every two to seven years.
Why is it called El Niño?
The phenomenon was first noticed by South American fishermen in the 1600s. Since it tended to happen around Christmas, they named it El Niño, a Spanish reference to the Christ child.
How does El Niño affect the weather?
It affects weather in different parts of the United States in different ways. Southern California, the Southwest and the Gulf Coast can expect a wetter winter, for example, while the Northwest and Upper Midwest will see a warmer winter.
Find out more about how meteorologists predict the weather from our science podcast, Brains On!
Why does warmer ocean water have such a significant impact?
The moisture put into the atmosphere by the abnormally warm ocean changes the path of the jet stream. "Think of the jet stream as the railroad tracks along which storms ride," explained weather forecaster Fritz Coleman. This shift causes some areas to have more storms and others to have fewer, as well as temperature changes.
What can we expect this year?
This year's El Niño is a strong one, so its effects will be more strongly felt. The last time El Niño was this strong was during the winter of 1997-98, when there was flooding in California and the Southeast, tornadoes in Florida and an ice storm in the Northeast.