The following is an excerpt from National Geographic.
The odds are in El Niño's favor. The U.S. Climate Prediction Center forecasts a greater than 50 percent chance that the climate-disrupting phenomenon could be upon us as early as this summer, with a two-in-three chance we'll be welcoming it by winter. Fingers are crossed in drought-ridden California, where a strong El Niño could increase rain and snowfall.
A debris flow damages a home after heavy rains caused mudslides in La Cañada Flintridge, California, in 2010. PHOTOGRAPH BY DAVID MCNEW, GETTY IMAGES
The last El Niño occurred in 2009-2010 and brought drought to Australia and rains to California. The weather pattern generally occurs in cycles of two to seven years and is the warm extreme of the El Niño/Southern Oscillation (ENSO), the fluctuation in tropical Pacific Ocean temperatures. The cold phase of the oscillation is called La Niña. (Since El Niño tends to be especially strong close to Christmas, South American fishermen named the weather pattern after the Christ child.)