The above image shows the sea surface height and temperature difference from normal during January 1999, a period of La Niña. Abnormally warm water (shown in yellow and red) expands and raises the surface of the ocean, while cool water (shown in blue) shrinks. This can be seen in the trough of cool water extending westwards from South America. (Image courtesy Greg Shirah, Scientific Visualization Studios)

U.S. La Niña Impacts
The first three months of the year during a La Niña typically feature below normal precipitation in the Southwest, the central and southern sections of the Rockies and Great Plains, and Florida. Meanwhile, the odds of surplus precipitation increase across the Pacific Northwest, in the northern Intermountain West, and over scattered sections of the north-central states, Ohio Valley, and upper Southeast. La Niña features unusually cold weather in the Northwest and (to a lesser extent) northern California, the northern Intermountain West, and the north-central states. Farther south, higher than normal temperatures are slightly favored in a broad area covering the southern Rockies and Great Plains, the Ohio Valley, the Southeast, and the mid-Atlantic states.

Global La Niña Impacts
Globally, La Niña is characterized by wetter than normal conditions west of the equatorial central Pacific over northern Australia and Indonesia during the northern hemisphere winter, and over the Philippines during the northern hemisphere summer. Wetter than normal conditions are also observed over southeastern Africa and northern Brazil, during the northern hemisphere winter season. During the northern hemisphere summer season, the Indian monsoon rainfall tends to be greater than normal, especially in northwest India. Drier than normal conditions are observed along the west coast of tropical South America, and at subtropical latitudes of North America (Gulf Coast) and South America (southern Brazil to central Argentina) during their respective winter seasons.

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La Niña
The Southern Oscillation
The Effects of La Niña
NASA and NOAA Missions to Study La Niña

Related Data Sets:
Sea Surface Temperature
Rainfall