The National Oceanic and Atmospheric Administration’s Climate Prediction Center says there is a 60% chance that a weak La Nina event will develop this fall and could last until March.

La Nina is part of a natural climate cycle that can cause extreme weather across the planet – and its effects vary from place to place.

While there is no guarantee how this La Nina will play out, there are some general trends. Experts say northern parts of South America could see more rain than normal. The southern regions of the US and parts of Mexico can be drier than average. The northern part of the US and southern Canada can be wetter than average.

La Nina is the cool phase of the El Nino-Southern Oscillation, a naturally occurring global climate pattern that brings changes in wind and ocean temperatures in the Pacific Ocean and can cause extreme weather across the planet.

El Nino is the warm phase and occurs when the trade winds that typically blow across the Pacific Ocean toward Asia weaken, allowing warm ocean water to build up along the western edge of South America. But during La Nina, the trade winds strengthen and cold water rises from the depths of the sea, resulting in cooler-than-average ocean temperatures in the eastern Pacific.

These cold ocean temperatures and changes in the atmosphere affect the position of the jet stream – a narrow band of fast-moving air that flows from west to east around the planet – by nudging it north. The jet stream sits above the ocean and can tap into its moisture, influencing the path storms take and boosting precipitation.

Recently, Earth experienced a “triple-dip” La Nina event from 2020 to 2023. “We had three consecutive winters where we had La Nina conditions, which was unusual because the only other instance of that event occurred during 1973 -1976 played. ,” says Michelle L’Heurex, climate scientist at NOAA. L’Heurex said La Ninas tend to last longer and occur more frequently than El Nino events.

“It’s unusual, but not unprecedented,” said Ben Cook, a climate scientist at the NASA Goddard Institute for Space Studies at Columbia University, about the forecast for a possible La Nina this year.

Cook noted that the frequency of La Nina events could be stressful for regions that have suffered recent droughts, such as East Africa. “If we go to another La Nina event, it will kind of mean a continuation of those really bad conditions.”

La Nina weather influences

The influence La Nina has on the weather varies depending on the location and season, according to L’Heurex. Parts of South America, such as eastern Argentina, may be drier than average, while Colombia, Venezuela and northern parts of Brazil may be wetter than normal.

“It depends where exactly you are. Part of that is because there is a monsoon cycle, wet and dry season, that runs through Central America and South America, so La Nina actually changes the intensity and placement of those monsoon cycles,” L’Heurex explains.

In the U.S., conditions in the Northeast and Ohio Valley are generally wetter than normal, with an active storm track due to the jet stream’s position, said Samantha Borisoff, a climate scientist at NOAA’s Northeast Regional Climate Center, based at Cornell University.

The jet stream waves could also cause more frequent cold outbreaks, especially in the central and southern US. Borisoff said snowfall is difficult to predict and depends heavily on the storm and the path it takes, but noted that New England, New York and the Great Lakes region tend to have more snow during La Nina winters , but that is never a guarantee. The southern and southeastern regions of the US are further away from the active storm path and tend to be drier and warmer than normal.

La Nina, El Nino and climate change

Scientists say the link between climate change and La Nina and El Nino is not entirely clear.

Paul Roundy, a climate scientist at the University at Albany, said climate models generally point to more frequent El Ninos and less frequent La Ninas, but not all models agree. Computer models also struggle to separate the normal variation in the El Nino and La Nina phases from the warming influence of climate change on the oceans and atmosphere.

“I wouldn’t conclude from this that climate change isn’t actually causing more El Nino occurrences,” Roundy said. “It’s just that nature itself has such strong fluctuations. So we could have multiple La Nina events, and maybe in forty or fifty years we’ll see the opposite.”

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