The National Oceanic and Atmospheric Administration’s Climate Prediction Center predicts a 60% chance of a weak La Nina event developing this fall, potentially lasting until March.
La Nina is a natural climate cycle that can lead to extreme weather events around the globe. Its effects vary by location.
While there are no guarantees, general trends suggest northern parts of South America could see above-average rainfall. The southern U.S. and parts of Mexico might experience drier conditions than normal. Meanwhile, the northern tier of the U.S. and southern Canada could be wetter than usual.
La Nina represents the cool phase of the El Nino-Southern Oscillation, a natural global climate pattern characterized by changes in wind and ocean temperatures in the Pacific. This pattern can cause extreme weather globally.
El Nino, the warm phase, occurs when trade winds blowing across the Pacific towards Asia weaken, allowing warm ocean waters to accumulate near the western edge of South America. Conversely, during La Nina, trade winds intensify, forcing cold water from the ocean depths to rise, leading to cooler-than-average temperatures in the eastern Pacific.
These cold ocean temperatures and atmospheric changes impact the position of the jet stream, a narrow band of fast-moving air flowing from west to east around the globe. The jet stream, located over the ocean, can draw moisture from the water, influencing storm paths and increasing precipitation.
Recently, Earth experienced a “triple-dip” La Nina event from 2020 to 2023. “We had three back to back winters where we had La Nina conditions, which was unusual because the only other case of that happening was back in 1973 to 1976,” said Michelle L’Heureux, a climate scientist at NOAA. L’Heureux noted that La Nina events tend to last longer and occur more frequently than El Nino events.
“It’s unusual although it’s not unprecedented,” said Ben Cook, climate scientist at the NASA Goddard Institute for Space Studies affiliated with Columbia University, regarding the forecast for a potential La Nina this year.
Cook pointed out that the frequency of La Nina events can be challenging for regions experiencing drought, such as East Africa. “If we’re moving into another La Nina event, it means kind of a continuation of those really bad conditions.”
La Nina weather impacts
La Nina’s influence on weather varies depending on location and season, explained L’Heureux. Parts of South America, like eastern Argentina, may experience drier conditions, while Colombia, Venezuela, and northern Brazil could be wetter than normal.
“It depends exactly where you are. Part of that is because there’s a monsoon cycle, wet and dry season, that goes through Central America and South America, so La Nina is basically modifying the intensity and placement of those monsoon cycles,” explained L’Heureux.
In the U.S., the Northeast and Ohio Valley typically see wetter-than-normal conditions with an active storm track due to the position of the jet stream, according to Samantha Borisoff, climate scientist at NOAA’s Northeast Regional Climate Center based at Cornell University.
The waviness of the jet stream can also lead to more frequent cold outbreaks, particularly in the central U.S. Borisoff said snowfall is difficult to predict and highly dependent on the storm and path it takes, but noted that New England, New York, and the Great Lakes region tend to be snowier during La Nina winters, although this is not always the case. The southern and southeastern regions of the U.S. are farther away from the active storm track and tend to be drier and warmer than normal.
La Nina, El Nino and climate change
Scientists say the link between La Nina and El Nino and climate change is not entirely clear.
Paul Roundy, climate scientist at the University at Albany, said climate models suggest more frequent El Ninos and less frequent La Ninas, but not all models agree. Computer models also struggle to distinguish normal variation in the El Nino and La Nina phases from climate change’s warming influence on the ocean and atmosphere.
“I would not infer from that that climate change isn’t actually causing more El Nino emergence,” Roundy said. “It’s just that nature itself has such strong swings on its own. So we can get multiple La Nina events, and maybe in 40 or 50 years we’ll be seeing the opposite.”
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