LOS ANGELES -- Floods in Southern California? Blame it on El Nino. Drought from the Great Plains to the Southeast? Sounds like La Nina. Nervous climate forecasters? Must be "La Nada."
For the first time in three years, the tropical Pacific Ocean isn't running unusually hot or cold, and the neutral conditions are leaving climatologists with fewer pieces of the puzzle. Gone are the heady days of confident predictions months into the future.
"There comes a time when you have to admit your understanding is not complete and not to say more than you know," said William Patzert, an oceanographer at NASA's Jet Propulsion Laboratory. "It's hard after three years of being a hotshot. It's really hard."
Unlike El Nino and La Nina years, nothing appears strong enough to dominate the complex climate system.
That means the effects of relatively small forces such as the moisture of an individual storm could determine whether an area is wetter or drier or warmer or cooler than usual.
"So the forecast problem becomes much more difficult, much more challenging," said Vernon Kousky, a research meteorologist with the National Oceanic and Atmospheric Administration's Climate Prediction Center.
"We don't anticipate that we will have such a high level of skill as we had in recent years," he said.
Forecasters are having to focus on historical records and weaker signals from the oceans for hints to the upcoming stormy season and beyond.
For the record, climatologists predict a slightly warmer-than-normal winter for much of the United States. They're less certain about the Northern border states, where decisions must be made on whether to stock up on home heating oil and road salt.
During El Nino years like the winter of 1997-98, westward-blowing trade winds weaken, allowing a mass of warm water in the western equatorial Pacific to flow eastward toward South America. Sea surface temperatures can surge as much as 14 degrees above normal.
In a complicated chain of events, the warmer water leads to record rainfall in California, tornadoes and flooding in the Southeast, flooding in Peru, and drought and wildfires in Indonesia.
La Nina occurs when the trade winds strengthen and the equatorial Pacific cools as much as 8 degrees. The La Nina pattern has dominated since the end of the last El Nino in 1998.
The signal isn't as strong as an El Nino, but forecasters can confidently predict storms will be pushed farther north, creating drought conditions in the Southeast and Central United States.
Patzert, who studies sea surface temperatures with the U.S.-French Topex-Poseidon satellite, calls the current condition that developed in August "La Nada." Others joke about "No Nina." Officially, it's "El Nino Southern Oscillation Neutral."
Researchers are looking to other systems that could influence the climate, such as the Arctic Oscillation that appears to flip-flop between higher-than-normal pressure and lower-than-normal pressure over the polar region.
One phase is suspected of steering ocean storms farther north and carrying wet weather to Alaska, Scotland and Scandinavia but drier conditions to California, Spain and the Middle East. The negative phase has opposite results.
The problem this year is that the Arctic Oscillation also appears to be in a neutral mode, and there's no way to forecast when it will change.
"It jumps around a lot," Kousky said. "It sometimes locks into a certain phase in January and continues through March, but there's no way we can anticipate that in advance. At least we haven't found one yet. We're working on it."
Then there's the Pacific Decadal Oscillation, also known as the North Pacific Oscillation, that is suspected of being related to short-term El Ninos and La Ninas but covers a period of decades rather than months or years.
Earlier this year, researchers announced the oscillation may have switched to a new phase that favors La Nina events over El Ninos, or simply weaker El Ninos. It appears as a warm tongue of water extending from Japan across the Pacific, surrounded by cooler-than-normal water along the Aleutian Islands, the coast of North America and the tropics.
Under the current oscillation condition, locations north of a line drawn from San Diego to Boston could see cooler conditions than normal while places to the south could experience warmer conditions.
"Unfortunately, its impact is often not terribly strong, and the chaotic atmosphere can overwhelm it," said Tim Barnett, an oceanographer at the Scripps Institution of Oceanography. "It's not as strong an impact as El Nino, but it's something anyway."
On the Net:
Climate Prediction Center: http://www.nnic.noaa.gov/cpc/
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