This summer has been memorable for what we did not see: A persistent heat dome parked over the Lone Star State, driving weeks of triple-digit heat. Instead, a series of storm systems brought intermittent showers and thunderstorms throughout the season.
The milder weather pattern reflects a neutral phase of the El Niño-Southern Oscillation, which occurs in the equatorial waters of the eastern Pacific Ocean. This means that neither La Niña (the cooling phase) nor El Niño (the warming phase) was present and did not steer our summer weather pattern to the extremes with drought or heat.
But what does all of that mean? How does this affect us in Austin and Central Texas? Let's break it down:
ENSO is a global climate driver that can significantly influence the weather in the United States, especially in winter. Because the atmosphere is an interconnected system across the globe, weather events in one spot can have a ripple effect in another part of the world.
With ENSO, you're seeing significant sea-surface temperature changes, which are the result of major shifts in heat energy, in the world's largest ocean that contains most of the planet's water. So, it should be no surprise that El Niño/La Niña events in the eastern Pacific can affect Texas weather.
This is important now because the latest update from the forecast team at the National Weather Service's Climate Prediction Center narrowly favors a gentle shift from ENSO-neutral to La Niña conditions by this fall and winter, which means that the tropical waters in the eastern Pacific Ocean are forecast to be colder than average by 1 degree.
They state that the La Niña thresholds are being reached in three overlapping, three-month seasons, and now has placed the United States under a La Nina watch. This is issued when conditions are favorable for the development of La Niña conditions within the next six months.
During La Niña, unusually strong Pacific trade winds push warm surface water westward toward Asia, enhancing an upwelling of deeper seawater along the Americas that forces colder, nutrient-rich water to the surface.
This weather pattern nudges the jet stream north, leading to stormier conditions in the Pacific Northwest and warmer, drier weather across the southern United States, which includes Texas.
A shift to La Niña during the Atlantic hurricane season often leads to more storm activity in the tropical Atlantic, Caribbean Sea and the Gulf of Mexico.
The critical factor is vertical wind shear, which is the change in wind speed and direction as you go higher into the atmosphere, according to the National Oceanic and Atmospheric Administration. Strong shear can tear apart developing tropical systems or prevent them from forming and weak shear allows storms to organize and sustain their energy.
La Niña conditions in the Pacific tend to decrease wind shear in the Atlantic Basin, which then increases the chances of tropical cyclone development.
The Climate Prediction Center's fall outlook reflects the typical shift in Texas weather patterns, calling for drier conditions than normal from September through November.
Austin in September averages a high temperature near 91 degrees and a low temp near 70 degrees with about 3.45 inches of rain. In October, the average high temp is 83 and the average low is 61 degrees, with roughly 3.91 inches of rainfall. By November, averages cool to 72 and 51 degrees with around 2.92 inches of rainfall.
Even with La Niña expected this fall and winter, cold snaps and wintry weather are still possible. Last year, a January winter storm struck during a La Niña winter, and the major freeze in February 2021 also occurred under La Niña conditions.