New satellite data released by NASA on Thursday show that the Pacific Ocean is in the grips of one of the strongest La Niña weather systems in the last 50 years, bringing deadly flooding to Australia.
But La Niña's effects in California and the West Coast have so far been muted, and experts are not exactly sure why.
The climatological phenomenon, marked by cooler-than-normal sea surface temperatures in the equatorial Pacific, usually brings heavy rainfall to places such as Australia, Indonesia, Brazil and Colombia while bringing unusually dry periods to California and the southern United States.
California, however, has been experiencing record rainfall and snow, leading some to question whether the La Niña forecasts were a bust.
Forecasters say the NASA data — and the Australia flooding — show La Niña is clearly a major force this year. And they said it's still possible that the rest of the winter will be unusually dry in California. Since 1949, more than 80% of La Niñas have produced dry winters in Southern California.
"It's not a bust till we get through the entire year," said Eric Boldt, a meteorologist for the National Weather Service in Oxnard.
Since July 1, more than 12 inches of rain has fallen in Los Angeles. That's about 7 inches more than normally falls by this point of the year. December was the wettest in downtown L.A. in more than a century.
But Bill Patzert, a climatologist with the Jet Propulsion Laboratory in La Cañada-Flintridge, pointed out that much of the rainfall so far can be explained by one freak week in December.
He said that was when a strong jet stream from the Gulf of Alaska pounded Southern California with almost nonstop rain. The so-called Arctic oscillation was potent enough to negate any of La Niña's effects, he said.
"It's been very dry this rain year since July," he said, "except for that week in December."
Patzert said he's still betting that the remainder of the winter will turn dry. The reason, he said, is that although the wet Arctic oscillation has a relatively short shelf life, the strong La Niña event could linger into the spring and summer.
"In the known historical record, this definitely ranks as one of the strongest La Niñas," Patzert said. "It's a strong La Niña, and having a strong La Niña impacts the tropics and subtropics" with more rainfall.
Flooding has killed at least 25 people in Australia's Queensland state, and 60 others are missing. On Thursday, officials said that up to 30,000 homes and businesses in Brisbane were hit by water and mud. Videos showed entire neighborhoods underwater, with trash cans floating down streets and residents surveying ruined furniture and other valuables.
But La Niña hasn't asserted itself in the United States yet, Patzert said. A lot of precipitation in the northern states, including New York, is a hallmark of La Niña, but not the frigid, blizzard conditions many of those states have experienced, he said.
Still, he said, he thinks at some point La Niña could bring to Southern California what it has done 18 out of the last 22 times it has appeared: a dry streak.
Boldt, of the weather service, agrees that could well happen, even though thunderstorm activity in the western Pacific could move into the area closer to February.
"Right now we're well above normal for rainfall," he said. "But now we're in January, and so far it's looking pretty dry."