Tracking the El Niño Southern Oscillation
Earth’s oceans cover about 71% of the planet, making these vast bodies of water highly influential when it comes to weather and climate. The El Nino Southern Oscillation (ENSO) is an observed climate pattern based on sea surface temperature trends in the tropical Pacific. Phases of the ENSO ebb and flow from year to year, impacting dominant weather patterns across large parts of the globe, including North America. Three primary phases of the ENSO are El Niño, La Niña, and neutral.
Earlier this week, the Climate Prediction Center announced a notable advancement in how the ENSO will be classified and predicted going forward. This involves a change in the index used to determine and track phases of the ENSO. Rather than using the Oceanic Niño Index (ONI), the CPC is adopting the Relative Oceanic Niño Index (RONI).
The previously used ONI relies only on 30 year averages to measure temperature departures in a specific region of the tropical pacific and ultimately classify the ENSO phase. This method does not account for any recent changes in sea surface temperatures across the tropics as a whole. The newly adopted RONI solves this problem by comparing temperature changes over the same specified region to a much larger swath of the tropical pacific.
According to the Climate Prediction Center, “RONI provides a more stable and physically meaningful measure of El Niño and La Niña conditions in real time”. This ultimately means ENSO forecasts could become more accurate and better fit traditional definitions when it comes to regional trends and impacts associated with each phase.
The ENSO generally has a greater impact on weather patterns in the Northern Hemisphere during winter, mainly due to changes in the jet stream. La Niña winters are known to bring colder and snowier conditions across the northern tier of the United States, with better chances for warmer drier weather down south. By contrast, El Niño winter seasons can promote warmer and drier than normal conditions across parts of the northern U.S. with cooler and wetter conditions further south. ENSO-neutral conditions typically mean less major changes in the jet stream, with less defined trends in temperature and precipitation over the continental United States.
Because Northwest Missouri and Northeast Kansas lie near the center of the United States ENSO trends tend to be less consequential compared to the far north or deep south. La Niña has been in place for the 2025 - 2026 winter season thus far. Over the next few months, a transition to ENSO neutral conditions is expected to occur.
