It looks like a La Niña event is coming. Here's how it will affect the US weather

There is a 60 percent chance of a La Niña event occurring this year, which could last until March 2025.

La Niña is part of a climate cycle that causes extreme weather changes worldwide, the effects of which vary from place to place. It is the cool phase of the El Niño Southern Oscillation that causes changes in wind and ocean temperatures in the Pacific.

During an El Niño (which means “little boy” in Spanish), the trade winds that normally move across the Pacific into Asia weaken, causing warm seawater to build up on the western edge of the Americas. However, in La Niña (“little girl”), these trade winds become stronger and bring cold water from the depths of the ocean to the surface (a process called “upwelling”), resulting in cooler temperatures in the eastern Pacific. These colder temperatures then affect the position of the jet stream – a strong core wind that blows across the planet from west to east – which is pushed further north.

Once this shift in the jet stream occurs, storms become wetter as they absorb more moisture from the ocean. This tends to lead to more droughts in the southern United States and heavy rains and flooding in the Pacific Northwest and Canada. La Niña can also lead to harsher hurricane seasons.

In general, El Niño is more common than La Niña, but between 2020 and 2023 the world experienced a rare “triple-dip” La Niña event.

“We had three consecutive winters where we had La Niña conditions, which was unusual because the only other case where something like that happened was in 1973 to 1976,” says Michelle L'Heurex, a climate scientist at the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center told AP.

Although it looks like a fourth La Niña event is on the way, forecasters expect it to be weaker as it appears to develop later in the season than usual. However, many models seem to indicate that this is the case.

“Due to the warmer forecast and recent weakening of the equatorial trade winds, the team still favors a weak event but has lowered the likelihood of La Niña,” NOAA explains. “A weaker La Niña means traditional winter impacts would be less likely to occur, although predictable signals could still influence the forecast.”

“In summary,” they say, “La Niña is expected to occur in September-November (60 percent chance) and is expected to last until January-March 2025.”