If you’ve been tuned into Tennessee Valley Weather for any amount of time, there may have come points in which you’ve heard us reference those two Spanish terms (translating to “The Girl” and “The Boy”) in the context of long-range forecasts and pattern shifts – alternatively, you may even remember hearing these terms in science class years ago in school. But what exactly are these terms referring to? How do they impact global forecasts in such broad ways? Let’s break it down.
At their most base levels, these phenomena are controlled by the broader ENSO, or El Niño-Southern Oscillation, cycles centered over the central Pacific Ocean, which describes the various states of trade wind patterns in this region, as well as the accompanying sea surface temperature fluctuations dictated so often by those trade winds. At it’s most basic level, the warming phase of the sea surface temperature is known as “El Niño” and the cooling phase as “La Niña“. It’s also worth noting that there is a “Neutral” phase as well, in which the region falls into a pattern of being around the climatological average with neither extreme prevailing. The Southern Oscillation is the accompanying atmospheric variations, which are themselves directly correlated with the sea temperature change.
Though we are of course many thousands of miles from the Equatorial Pacific ocean, these subtle changes to sea surface temperature changes, trade winds, and subsequent surface air pressures have major downstream effects in true butterfly effect style (fun fact: the notion of the butterfly effect was first described by a Meteorologist!). One of the big controllers of our weather in the Continental United States, the polar jet stream, because rather variable and pronounced often times during La Niña winters, leading to wetter precipitation patterns locally in our neck of the woods. On the other hand, an El Nino pattern often leads to higher pressure conditions on average in the north, which leads to a warmer winter in the north thanks to a less variable polar jet stream and consequently can lead us into drier patterns. It’s worth noting that there can be dry La Niña winters, and wet El Nino winters, but the aforementioned pattern trends are just that – trends. All it takes is one exception to throw a forecast all awry, especially because ENSO patterns aren’t predictable at significant time ranges, but there is enough comprehensive data dating back decades to put together “typical” outcomes for both. This Winter, model projections indicate La Niña conditions are expected to continue until around February 2026 and as a result the Climate Prediction Center has put out a La Niña advisory, so we will watch the seasonal forecasts closely… and we’ll let you know if we notice trends towards wetter, warmer, or colder conditions or anything inbetween.
