In the Eastern Pacific, normal conditions see trade winds blow west across the equator, which leads to warmer waters being pushed west towards Asia, and cooler, more nutrient-rich waters upwelling from the depths to replace it of the west coast of North and South America. During El Niño, this process sees a reversal, where the warm water piles up further east, closer to the Americas. La Niña is the opposite where the trade winds are even stronger than normal, and the water off the coast of South America is colder than normal. Since this summer, we’ve been seeing the water in the Eastern Pacific get colder as a La Niña develops.
This pattern of El Niño, La Niña, and neutral is a normal oscillation in our atmosphere and ocean called the El Niño Southern Oscillation (ENSO). When we enter an El Niño or La Niña as we head into winter, we can get some clues as to how the weather will behave through the winter.
In many La Niña winters, the weather in the southeast is warmer and drier than normal. That’s exactly the forecast from the Climate Prediction Center as we move through the last 3 months of 2021.
There’s often some variability between La Niña winters though, so we’ll have to keep an eye on where the coldest water sets up and how the jet-stream reacts as we head into the winter months.