La Niña is part of a natural climate cycle that can cause extreme weather across the planet—and its effects vary from place to place.

Although there is no guarantee how this La Niña will play out, there are some general trends. Experts say northern parts of South America could see more rain than usual. Southern regions of the U.S. and parts of Mexico could be drier than average. The northern tier of the U.S. and southern Canada could be wetter than average.

La Niña is the cool phase of the El Niño-Southern Oscillation, a naturally occurring global climate pattern that involves changes in wind and ocean temperatures in the Pacific and can cause extreme weather across the planet.

El Niño is the warm phase and happens when trade winds that typically blow across the Pacific toward Asia weaken, allowing warm ocean waters to pile up along the western edge of South America. But during La Niña, the trade winds intensify and cold water from the depths of the sea rises up, resulting in cooler than average ocean temperatures in the eastern Pacific.

These cold ocean temperatures and changes in the atmosphere affect the position of the jet stream—a narrow band of fast moving air flowing from west to east around the planet—by bumping it northward. The jet stream sits over the ocean and can tap into its moisture, influence the path storms take and boost precipitation.