You’ve probably heard your local weather forecaster talk about rain or storms caused by El Niño. But have you ever heard of La Niña?
La Niña, like El Niño, is a weather pattern that can occur in the Pacific Ocean every few years. In a normal year, winds along the equator push warm water westward. Warm water at the surface of the ocean blows from South America to Indonesia. As the warm water moves west, cold water from the deep rises up to the surface. This cold water ends up on the coast of South America.
In the winter of a La Niña year, these winds are much stronger than usual. This makes the water in the Pacific Ocean near the equator a few degrees colder than it usually is. Even this small change in the ocean’s temperature can affect weather all over the world.
Rain clouds normally form over warm ocean water. La Niña blows all of this warm water to the western Pacific. This means that places like Indonesia and Australia can get much more rain than usual. However, the cold water in the eastern Pacific causes less rain clouds to form there. So, places like the southwestern United States can be much drier than usual.
La Niña is caused by an interaction between the Pacific Ocean and the atmosphere above. However, it can have effects on weather all over the world. These changes in the atmosphere can lead to more lightning activity within the Gulf of Mexico and along the Gulf Coast. Also, the environmental conditions during La Niña can lead to more tropical cyclones—which include hurricanes—forming in the deep tropics (near the islands in the Caribbean, for example).
Thankfully, scientists can predict the El Niño and La Niña weather patterns up to a year before they occur. The GOES-R series of weather satellites can help weather forecasters map the increased lightning and issue earlier and more accurate severe weather warnings.