El Niño Definition Workshop

On December 2, 2002, NOAA, led by the NWS Climate Services Division, held an El Niño Definition Workshop in Silver Spring, Maryland. This workshop brought together El Niño experts to develop an operational NOAA definition for El Niño and La Niña. The definitions agreed upon follow.

El Niño: A phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño 3.4 region greater than or equal in magnitude to 0.5C, averaged over three consecutive months.

La Niña: A phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño 3.4 region greater than or equal in magnitude to 0.5C, averaged over three consecutive months.

NOAA began using the definitions operationally for monitoring and predicting El Niño and La Niña conditions on September 1, 2003. NOAA issues assessments of ENSO's status in the Monthly Climate Diagnostic Bulletin, the ENSO Diagnostic Discussion, and the Weekly ENSO update. Currently, NOAA is engaged in dialogue with the international climate community for global acceptance of the definitions.

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