A just-declared El Niño climate pattern not only is one possible cause for the unusually large amount of precipitation in recent weeks but may also mean a wetter spring than usual.

The National Oceanic and Atmospheric Administration officially announced Thursday that an El Niño had arrived in the equatorial Pacific and could continue through the spring.

NOAA has identified the above-average sea surface temperatures associated with the irregular weather pattern, but NOAA forecaster Mike Halpert said this El Niño will be weak and “we do not expect significant global impacts through the remainder of winter and into the spring.”

However, it could mean more rain and snow.

Storm culprits

The “atmospheric river” responsible for the recent series of storms could have several causes — El Niño, an equatorial atmospheric system known as the Madden Julian Oscillation (MJO) and typical local weather volatility, said NOAA climate scientist Michelle L’Heureux.

“The atmospheric river is likely a combination of all three,” L’Heureux said.

While El Niño is a seasonal, Pacific Ocean-based system lasting a few months to a year, the Madden Julian Oscillation is an atmospheric pattern of rain and winds that moves eastward around the globe at the equator and typically lasts a few weeks to a few months.

“It can enhance the effects of El Niño,” L’Heureux said. “We believe a lot of the rainfall can be linked to MJO.”

That rainfall has already delivered many parts of Southern California more precipitation than is usually delivered in an entire season. As of Thursday, John Wayne Airport had reported 15.8 inches of rain since Oct. 1. The average for a season there is 13.6 inches.

Climate change?

There’s no consensus on whether global climate change is having an effect on the strength and frequency of El Niño systems.

“It’s a real complicated question,” L’Heureux said. “Ocean temperatures are warming, but what’s not clear is whether that’s having an effect on El Niños.”