According to the Climate Prediction Center, the La Niña weather pattern has officially ended and we have entered an ENSO neutral period of this oscillating temperature and atmospheric pattern.

ENSO or El Niño Southern Oscillation conditions describe the coupling and connection between the atmosphere and ocean surface temperatures in the eastern equatorial Pacific Ocean. There are three phases to ENSO: El Niño, La Niña and neutral. These phases can act as indicators of what conditions (warmer/drier or cooler/wetter) we could see, mainly in the winter.

La Niña conditions exist when water temperatures are significantly cooler than normal in the eastern equatorial Pacific Ocean.

Conversely, when ocean temperatures in the eastern Equatorial Pacific are significantly warmer than normal, then we enter the El Niño phase.

Sea Surface Temperature anomalies over the past few months in the various Niño regions of the Equatorial Pacific. (Courtesy: Climate Prediction Center)

Ocean temperatures, especially in the “Niño 3.4” region of the Equatorial Pacific used to diagnose an El Niño or La Niña event, were at their coolest levels in November 2020. An anomaly of -1.8°C qualified this, at least briefly, as a strong La Niña.

The Oceanic Niño Index or ONI is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO.

La Niña: characterized by a negative ONI less than or equal to -0.5ºC.

El Niño: characterized by a positive ONI greater than or equal to +0.5ºC.

By historical standards, to be classified as a full-fledged El Niño or La Niña episode,
these thresholds must be exceeded for a period of at least five consecutive overlapping
three-month seasons.

Since November 2020, the surface water temperatures in that region have been warming. Currently the sea surface temperature anomaly in the Niño 3.4 region is -0.4, which no longer puts us in a La Niña category.

When conditions return to ENSO-neutral then there is a much weaker coupling between the atmosphere and the water temperatures in the equatorial Pacific Ocean.

The official ENSO forecast is for neutral conditions to continue through summer in the Northern Hemisphere.

Another La Niña on the way?

According to the Climate Prediction Center, La Niña is just slightly favored over a neutral or El Niño phase: “La Niña chances are around 50-55% during the late fall and winter, which is in alignment with forecasts from the NCEP Climate Forecast System and North American Multi-model Ensemble.”

IN DEPTH: ENSO’s impact on Texas

El Niño and La Niña weather patterns typically have more of an effect in the colder months here in Texas and throughout the United States.

In an El Niño winter, the weather in Texas is typically wetter than average.

El Niño Winter

Conversely a La Niña winter is drier for most of Texas.

La Niña Winter

During an ENSO neutral pattern, the water temperatures in the eastern Equatorial Pacific don’t have a noticeable impact on our weather. You can take this to mean that a) generally normal weather is expected or b) other atmospheric factors and climate changes will be the main drivers in our weather.