What is El Niño?

El Niño is a periodic warming of the tropical Pacific Ocean that can alter weather patterns worldwide. During El Niño winters, changes in tropical rainfall and atmospheric circulation often strengthen and shift the Pacific jet stream southward, increasing opportunities for winter storms across the southern United States.

For Arizona and New Mexico, El Niño tilts the odds toward a wetter-than-average cool season, but it does not guarantee a wet winter. The position and persistence of the storm track ultimately determine where storms travel and how much precipitation falls. Even subtle shifts in the storm track can direct the bulk of the precipitation north or south of the region or produce very different outcomes within the Southwest, such as between northern and southern Arizona.