El Nino is officially here. What does that mean for U.S. weather?

El Nino has arrived in 2019. So far, it’s pretty weak. That doesn’t mean it will stay that way. 

The National Oceanic and Atmospheric Administration (NOAA) announced Thursday that this natural climate phenomenon — which is triggered by warmer temperatures in the equatorial Pacific Ocean and can significantly affect weather in the U.S. — will likely persist through the spring. But what happens next is still unclear.

“We don’t have a good handle on where this goes the rest of the year,” Mike Halpert, the deputy director of NOAA’s Climate Prediction Center, said in an interview. “It becomes kind of a tossup after spring.”

El Nino events happen when the warmer temperatures on the surface of the Pacific Ocean pass heat to the atmosphere, resulting in warmer air that naturally holds more moisture. “This allows more moisture to come to the U.S.,” Jeff Weber, a meteorologist with the University Corporation for Atmospheric Research, said in an interview.

Typically, this means above-average rain and snow across the southern regions of the United States, especially California. Conversely, the northern U.S. often sees less precipitation and warmer-than-average temperatures. 

“That is what we expect in the next spring months,” said Weber. 

Already, the West Coast has been pummeled by rain and snow events this winter, meaning up to 15 feet of snow in the Sierra Nevada Mountains and 8 inches of rain in some California areas. El Nino conditions may have contributed to these big precipitation events, noted Weber. Though, NOAA found that another climate phenomenon, the Madden Julian Oscillation, has also contributed to the wet season in some places. 

On Thursday, the West Coast got slammed by a storm, as a “conveyor belt” of moisture swamped the Golden State.

Big El Nino events — in which the ocean warms significantly more than this year — have planetary-wide consequences. Good examples are the big El Nino events of 2016-2017 and 1998-1999.

“Those have a big footprint on global annual temperatures,” noted Halpert.

Although such a mighty El Nino event isn’t in the cards this year, when it does happen, the vast Pacific Ocean adds enormous amounts of heat to Earth’s atmosphere. 

“That adds to the overall heat content of the planet, so to speak,” said Weber. 

El Nino events also have big implications for hurricane season in the U.S. Specifically, higher atmospheric winds (known as the jet stream) kick up over the southern U.S. during El Nino years, which can doom hurricanes. 

“These winds tear apart hurricanes,” said Weber. 

As of now, however, there’s still scant evidence that this weaker El Nino will last beyond spring. Hurricane seasons — which have been historically devastating in recent years — begin in early June. 

NOAA will keep watch over how this El Nino develops over the coming months. For now, temperature’s in the Pacific are a bit warmer than average (about 1 degree Fahrenheit or 0.5 degrees Celsius), but not quite enough to portend big changes — yet.

“I wouldn’t necessarily say this event has a big impact unless the [El Nino] event really takes off,” said Halpert.