California’s seasonal weather is influenced by El Niño and La Niña – temporary climatic conditions that, depending on their severity, contribute to weather that is wetter or drier than normal.

Although El Niño conditions can bring above-average precipitation to California in the winter, that is not always the case. Strong El Niño years tend to see wetter conditions in Northern California.

El Niño is characterized by unusually warm water temperatures in the Pacific Ocean at the equator. El Niño’s storm track affects the location of jet streams. Instead of coming ashore in the Pacific Northwest, the southern jet stream hits California with increased rainfall that is typically accompanied by floods, landslides and coastal erosion. El Niño tends to make atmospheric rivers stronger. El Niño events in 1982-1983 and 1997-1998 drenched the West Coast with record rain.

El Niño means the little boy or Christ child in Spanish. The name was chosen based on the time of year (around December) during which these warm water events were historically observed off the coast of South America. El Niño is the warm phase of a larger phenomenon called the El Niño-Southern Oscillation (ENSO), a periodic fluctuation in sea surface temperature and the air pressure across the equatorial Pacific Ocean.

La Niña, which means the little girl in Spanish, is the opposite of El Niño, with a cooling of the ocean surface in the central and eastern tropical Pacific Ocean. La Niña winters typically result in dry conditions for Southern California.

El Niño and La Niña episodes typically last nine to 12 months, but some events may last for years. While their frequency can be quite irregular, El Niño and La Niña events occur on average every two to seven years. Typically, El Niño occurs more frequently than La Niña, according to the National Oceanic and Atmospheric Administration.