El Niño and La Niña have their strongest impact on global climate during the Northern Hemisphere winter and early spring. El Niño and La Niña are opposite patterns. El Niño warms, and La Niña cools large areas of the tropical Pacific, which influences where and how much it rains there. This disrupts the atmospheric circulation patterns, which affect the mid-latitude jet streams. By modifying the jet streams, ENSO can affect temperature and precipitation across the United States and in other parts of the world.