El Ninos form when trade winds abate and water temperatures rise in the tropical Pacific Ocean. (Craig Miller)
Though it's still early in the game, forecasters say all the elements are in place for a whopper El Niño that could bring substantial rain and snow to California this fall.
Federal forecasters say there is now a 90 percent chance that the warm-water ocean conditions will prevail into the fall, and an 85 percent chance that they'll endure throughout the coming winter.
"It’s quite well established now in the Eastern Tropical Pacific Ocean and it appears to be strengthening," says Stanford climate scientist Daniel Swain, author of the popular California Weather Blog.
Now forget that you read this.
One of California's top water regulators recently complained that El Niño hype last spring threw a monkey wrench into efforts to promote water conservation.
"This killed us at the beginning of 2014," Felicia Marcus told reporters in a May conference call. Marcus heads the State Water Resources Control Board, which has been charged with implementing Governor Jerry Brown's statewide water restrictions.
"Everybody wrote the story that El Niño might save us, so people didn't start conserving when they should have."
As it happened, last year's El Niño, eventually dubbed "El Wimpo" by weather wags, remained too weak to overcome the prevailing drought conditions; the hoped-for rains never arrived.
"You can hope for it but you certainly can't plan for it," said Marcus.
But scientists say this year looks more like the real deal.
"Everything is certainly in place for this event to continue," says Mike Halpert, deputy director of NOAA's Climate Prediction Center.
"Right now the indications are that it will continue to strengthen and that this will be in place, in fact, next winter," agrees Swain.
But that question of strength is crucial. As we've reported here before, only the stronger El Niños translate to wet winters in California. Strength is measured according to how much ocean temperatures deviate from the norm. The difference between one degree and two degrees Celsius above average can be enormous in the "teleconnections," the term scientists use to describe distant weather effects from El Niño. Right now this one appears to be building strength.
"It still doesn’t mean that it’s a slam dunk strong El Niño forecast," says Swain, "but it does mean that this year we have higher confidence than we did last year."
Some of that confidence is driven by the atmospheric effects of the current El Niño, a connection that never quite took hold last year. What's happening in the ocean now is encouraging -- but it has to keep happening for several months to come.
Halpert says there's a slightly better-than-even chance that we'll see a strong event take shape. But while it's tricky enough to forecast the staying power of an El Niño, handicapping its strength several months hence is even harder.
"I think it takes more than just having the pieces," he cautions.
"I think it almost takes some level of — I hate to use the word luck -- but that somehow everything just falls together and that’s just not something that we’re able to forecast."
Get the best of KQED's science coverage in your inbox weekly.