Few things in the world of Southern California weather generate more curiosity, research, debate and occasional trash talk than El Niño.
El Niño storms have brought some of the region's heaviest drenchings, but experts say they are also among the most fickle, misunderstood and misinterpreted of weather phenomena.
With California in a severe drought, El Niño is often mentioned longingly as a savior. But it's not that simple.
Take this week's rain. It came from the kind of warm, subtropical storm often served up during an El Niño year. So was it an El Niño storm?
Answering that question is tricky, said Kathy Hoxsie, a meteorologist for the National Weather Service in Oxnard. "It's a component. It can help enhance rainfall amounts…. But we always steer away from the word 'caused,'" Hoxsie said.
El Niño occurs when weak trade winds build in the Pacific Ocean and sometimes create conditions that usher in warm storms. But the association is based largely on two anomalous events in the 1980s and 1990s in which El Niño years saw massive rainfall.
In the 64 years since scientists began studying the ocean weather pattern, there have been fewer than two dozen El Niños, and they have produced wildly inconsistent rain results. If the past is a predictor for the future, scientists say, Californians would be wise not to pin their drought-relief hopes on El Niño.
"When you look at weak-to-moderate El Niños, it's like a 50-50 split for more rain or less rain," said John Dumas, the National Weather Service science and operation officer for the National Oceanic and Atmospheric Administration.
Of the 22 El Niños since 1950, eight were weak, eight were moderate, and only six were considered strong. Five of the strong El Niños developed before winters that produced 40% more rain than normal in L.A.
Averaged together, however, El Niño years have generated slightly more than the city's average of about 15 inches of rain.
The driest rain year in Los Angeles' recorded history — July 1, 2006, to June 30, 2007 — happened during a weak El Niño. The second-wettest year on record in L.A. — 2004-05 — also happened during an El Niño year. But those storms were cold Arctic ones.
The two most powerful El Niños in the last 34 years formed in 1982 and in 1997. Storms drenched the state in the winters that followed, and caused floods that dominated national television news.
The storms that followed the 1982 El Niño jammed freeways, flooded neighborhoods, knocked down trees and power lines, damaged homes, caused mudslides and even generated a tornado in South L.A. More than 31 inches fell in L.A. during the 1982-83 rain year. The scene repeated in 1997-98, when 31 inches of rain fell, including almost 14 in February alone. El Niño was a kind of meteorological rock star.
To many Californians, those wet years are what El Niño looks like. But scientists say that in weaker El Niño years, it's far more difficult to say that increased precipitation resulted from an El Niño, from other meteorological factors, or from a combination of both.
That's the problem, scientists say, with predicting increased precipitation based on El Niños. Only very strong El Niños come with a virtual guarantee of significantly increased precipitation. Strong El Niños are generally those with substantially warmer sea-surface temperatures that persist above normal for months.
Early last spring, growing bands of warm waters in the Pacific Ocean — the hallmarks of a potentially drought-relieving El Niño — appeared on weather forecasters' computer screens and put many scientists in a hopeful mood. It looked like the patterns they saw in 1997.
And although scientists' hopes of a strong El Niño this year have faded away as winter approaches, that doesn't mean it won't rain more than normal.
Hoxsie said El Niño may have contributed to the precipitation this week. The waters in the Pacific are slightly warmer than normal now, and that means they are more likely to produce rain.
But the El Niño conditions are relatively anemic, so attributing the moisture to that weather pattern can be iffy.
Bill Patzert, who has long criticized El Niño forecasts, said he was intrigued enough by the strong early signs. He wrote a paper titled: "El Niño: Is 2014 the new 1997?"
But he had serious doubts about the El Niño forecast because his research indicated that the ocean seemed stuck in a long-term pattern aligned with drought.
On Thursday, NOAA forecasters said climate models show there is about a 65% chance that an El Niño will develop this year, but Patzert said the time for El Niño to be a force is over. If El Niño conditions develop in the next few months, he said, it would be a buildup for the 2015-16 winter, not this one.
For all the talk over the last nine months about El Niño, Patzert said, "conditions never reached the threshold for declaring even a weak El Niño.… It takes seven to eight months for a big El Niño to develop."
Patzert said that historically, El Niño rains come in late January through April.
Meteorologist Jan Null said that when the signs of El Niño looked impressive earlier this year, he was flooded with calls from people asking whether the drought was over. El Niño, like other climatological phenomena, he said, is not a great tool for long-term rain predictions.
"A third of the U.S. economy is weather-sensitive. If someone really had the answer to long-range forecasting, think how rich they could be. That person isn't out there. Nobody has the answer," he said.
Still, public fascination with El Niño continues. The Aquarium of the Pacific in Long Beach recently unveiled an exhibit dedicated to it.
Jerry R. Schubel, the aquarium's president and CEO, said its aim was to explain how El Niño works and align visitors' expectations with reality.
"We had placed too much hope in getting a strong El Niño to solve this drought problem," Schubel said. "It took several years to get us into this. It'll take several years to get us out."