UW News

January 17, 2002

Another El Niño could bring less rain to Northwest

News and Information

Another El Niño could be brewing in the equatorial Pacific Ocean. If it is, Pacific Northwest residents can expect generally warmer, drier weather next fall and winter, UW scientists say.

But it’s not clear that El Niño really is developing, even though the federal Climate Prediction Center last Thursday reported that waters in the equatorial Pacific are warming in a way that often produces the climate phenomenon.

“These same conditions have existed in weaker form for a long time, and they’ve been fooling the models for a long time. Maybe now it’s finally going to happen, or maybe those same conditions will persist and there won’t be an El Niño,” said Philip Mote, a research scientist with the Climate Impacts Group at the UW.

Mote said for the last year scientists have been monitoring a large area of warming water just beneath the surface of the Pacific along the equator around the International Date Line. The warming water recently has begun to spread to the east.

At times the conditions prompted some climate models to predict that El Niño was imminent, but the effect never developed.

But Nathan Mantua, also a research scientist with the Climate Impacts Group, said this time things appear to be different.

“For the past few months a number of factors have lined up in favor of an El Niño for later this year,” Mantua said. “Relatively large changes in upper ocean currents in the tropics almost guarantee some ocean warming in the tropical Pacific, and if these trends continue we could see an El Niño by this spring or summer.

“But, even though the odds now favor an El Niño for later this year, I wouldn’t bet the farm on it.”

The Climate Prediction Center, part of the National Oceanic and Atmospheric Administration, said El Niño could develop by early spring, but that impacts in the United States are unlikely before summer. The phenomenon has serious effects on weather worldwide. The agency also said the Pacific Northwest can expect wetter-than-normal conditions next fall—a forecast Mote said is unlikely and is exactly the opposite of what this region typically experiences with El Niño.

“The only scenario with a wetter-than-average fall is for El Niño to persist for only two or three months and then rapidly give way to La Niña,” he said. “But that is not the scenario that the El Niño models are predicting.”

La Niña is essentially the opposite of El Niño, developing when equatorial waters are colder than normal. Both are part of what is called the El Niño Southern Oscillation, or ENSO. While El Niño usually brings warmer, drier weather to the Northwest, La Niña typically means cooler and wetter conditions.

Mantua said that if an El Niño does develop this spring, “it would probably last into next fall or winter as happened in 1997 during the last El Niño. These events typically peak in early to mid-winter, and fade away during springtime.”

El Niño would have to compete with the Pacific Decadal Oscillation, or PDO, and other factors to influence Northwest weather in the next year, Mote said. The PDO has been in a cool phase for almost four years, nudging the region toward cooler, wetter conditions. But an El Niño event would bump the Northwest back toward normal conditions. During the last El Niño, the PDO was pushing Northwest conditions in the other direction.

El Niño commonly occurs every two to seven years and can last as long as a year. El Niño, Spanish for “little boy,” was named centuries ago by fishermen in Peru who noted its presence around Christmas and named it after the Christ child. The last El Niño, in 1997-98, was the second strongest on record and produced very severe weather conditions in parts of the United States, including drought in the Southeast and strong storms in California.

“This provides an early warning,” said Mantua. “We can’t be sure an El Niño will develop, but it’s certainly something we should be watching.”

Find out more at http://www.cses.washington.edu/.