A moderate El Niño is expected to develop this winter and will have an influence on our weather.
If you need a refresher, an El Niño occurs when sea surface temperatures are above average near the equatorial regions of the Pacific Ocean. The opposite is La Niña.
La Niña occurs when sea surface temperatures are running below average. These variations in sea surface temperatures can shift back and forth every two to seven years, which cause disruptions in air temperature, precipitation and wind.
For the Desert Southwest, these variations depend on whether we are experiencing El Niño or La Niña conditions.
This winter, a moderate El Niño is expected to develop. A moderate El Niño occurs when sea surface temperatures are running about 1.0 to 1.8 degrees Celsius above average. During an El Niño, we can expect to have slightly warmer temperatures with slightly above average precipitation. When La Niña is present, we tend to see less precipitation with cooler than average temperatures.
The National Weather Service, in Tucson, observes and records the variations in weather during El Niño and La Niña events. Our average rainfall, in Tucson, from December to February is 2.63 inches. The last time we had a moderate El Niño, in 2009-2010, we received 4.29 inches of rain. However, the moderate El Niño that occurred in 2002-2003, only brought 1.74 inches of rain. The trends vary, but history says our wet October trend may carry into winter. Better keep the rain gear handy!