The definition of La Niña is the cooling of the surface of the Pacific Ocean near the Earth's equator that happens at irregular intervals.
An example of La Niña is what causes unusually wet weather.
A cold-weather event, or cold episode, in contrast to El NiÃ±o, which is often referred to as a “warm event.” In the United States, La NiÃ±a causes winter temperatures that are warmer than normal in the Southeast and cooler than normal in the Northwest. The effects of both El NiÃ±o and La NiÃ±a are seen more in the winter than in the summer. La NiÃ±a impacts agricultural products and thus is watched by traders and others involved in agricultural commodities. Typically the effects last for several months to a year. La NiÃ±a is Spanish for “the little girl.” See also El NiÃ±o.