La Nina could arrive soon. Here's what that means for winter weather

According to the National Oceanic and Atmospheric Administration's Climate Prediction Center, there is a 60% chance of a weak La Nina event developing this fall that could last through March.

La Nina is part of a natural climate cycle that can cause extreme weather events around the world – and the effects vary from place to place.

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

La Nina is the cool phase of the El Niño-Southern Oscillation, a naturally occurring global climate pattern that brings changes in wind and ocean temperatures in the Pacific and can lead to extreme weather conditions around the world.

El Nino is the warm phase and occurs when the trade winds that normally blow across the Pacific toward Asia weaken, allowing warm seawater to accumulate on the western edge of South America. But during La Nina, trade winds intensify and cold water from the ocean depths rises, resulting in cooler ocean temperatures than 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 around the planet from west to east — by pushing it northward. The jet stream sits over the ocean and can harness its moisture, influencing the path of storms and increasing precipitation.

Most 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 since the only other case of such an event occurred in 1973 to 1976,” said Michelle L'Heurex, a climate scientist at NOAA . L'Heurex said La Nina events tend to last longer and occur more frequently than El Nino events.

“It's unusual, although it's not unprecedented,” Ben Cook, a climate scientist at NASA's Goddard Institute for Space Studies, affiliated with Columbia University, said of predicting a possible La Nina this year.

Cook noted that the frequency of La Nina events can be stressful for regions that have recently struggled with drought, such as East Africa. “If we move on to another La Nina event, that will mean a continuation of these really bad conditions, so to speak.”

Effects of weather on La Nina

The influence that La Nina has on the weather varies depending on location and time of year, L'Heurex said. Parts of South America, such as eastern Argentina, may be dryer than average, while Colombia, Venezuela and northern parts of Brazil may be wetter than normal.

“It depends exactly where you are. “That's partly because there is a monsoon cycle, a wet season and a dry season, that runs through Central and South America, so La Nina fundamentally changes the intensity and placement of those monsoon cycles,” L'Hurex explained.

In the U.S., the Northeast and Ohio Valley typically experience wetter conditions with an active storm track because of the position of the jet stream, said Samantha Borisoff, a climate scientist at NOAA's Northeast Regional Climate Center at Cornell University.

The jet stream's ripple may also lead to more frequent cold outbreaks, particularly in the central and southern United States. Borisoff said snowfall is difficult to predict and depends heavily on the storm and the direction it takes, but noted that New England, New York and the Great Lakes Region tend to see more snow in La Nina winters, but this is not a snowfall Guarantee. The southern and southeastern regions of the U.S. are further from the active storm track and tend to be drier and warmer than normal.

La Nina, El Niño and climate change

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

Paul Roundy, a climate scientist at the University of Albany, said climate models tend to point to more frequent El Ninas and rarer La Ninas, but not all models agree. Computer models also have difficulty separating the normal fluctuations in El Nino and La Nina phases from the warming influence of climate change on the oceans and atmosphere.

“I wouldn't conclude that climate change isn't actually leading to more El Niño events,” Roundy said. “It's just that nature itself has such strong fluctuations. So we could get multiple La Nina events, and maybe even more. In 40 or 50 years we will see the opposite.”

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