El Niño is a naturally occurring climate phenomena characterized by sea surface temperatures along the Equator in the Pacific Ocean. El Niño describes the warm phase of the El Niño-Southern Oscillation (ENSO), a recurring climate cycle where sea surface temperatures go through warm and cold cycles. The opposite phase, La Niña, occurs when sea surface temperatures in the region are cooler than average. ENSO is one of the most important drivers of global climate variability and can significantly influence weather in Missouri as well.

The first half of the 2020s was dominated by La Niña conditions. Aside from a moderate El Niño event that developed during late 2023 and persisted into spring 2024, Pacific Ocean temperatures were generally near or below average since 2020. During 2026, however, El Niño has re-emerged and strengthened rapidly. During 2026, El Niño has re-emerged and strengthened significantly this year. According to the U.S. National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC), El Niño conditions are currently present and are expected to intensify through the remainder of 2026.

One of the key indicators used to monitor ENSO is the Relative Oceanic Niño Index (RONI), which measures the sea surface temperatures in the Pacific Ocean. By July 2026, the RONI reached + 0.5 °C, meeting NOAA's threshold for the start of an El Niño event. Scientists are paying close attention to this event because forecasts indicate that it may become a one of the strongest El Niño events on record. Deeper waters in the Pacific are much warmer than normal and will fuel the continued warming of sea surface temperatures and forecasters expect this El Niño to strengthen during the coming months. Ocean forecast models predict El Niño to strengthen and peak during the late fall months. Most models predict sea surface temperatures will warm to greater than 2.0 °F above average, making it a very strong event. Many have referred to this event as a "Super El Niño" this summer. Recent strong events include 2015 (+ 2.4 °C), 1997 (+ 2.4 °C), 1992 (+ 2.3 °C), 1982-3 (+ 2.5 °C), 1972 (+ 2.3 °C), 1965 (+ 2.0 °C), and 1958 (+ 2.0 °C).

ENSO events have a global impact on weather patterns, including in Missouri (Figure 1). The Pacific Ocean is a significant source of global heat energy and small changes in temperature control pressure patterns with far-reaching impacts. Since ENSO evolves slowly over timescales ranging from seasons to years, it provides a climate signal that can help forecasters predict weather conditions months in advance. For producers, this information can be useful when planning for the growing season. The strongest relationships between ENSO and weather conditions are during the cooler months when large-scale weather systems moving across the country are steered by global pressure patterns. When summertime precipitation and weather are more local, there is less influence from El Niño or La Niña events (Figure 2).

Figure 1 (Source: NOAA (https://www.noaa.gov/climate))

Figure 2 (Source: NOAA Climate Prediction Center (https://www.cpc.ncep.noaa.gov))

In Missouri, there is a link between El Niño events and cooler temperatures and wetter conditions during the late summer and fall months. However, it is important to note that not all El Niño events are the same and there can be other years with dry and warm conditions. During colder months impacts are more certain. Missouri typically sees wetter winters and can see two different temperature scenarios. Northern Missouri has observed a tendency for more warmer winters during El Niño while southern Missouri can observe more cooler winters. The most recent strong El Niño event occurred in 2015-16 bringing wet conditions, a warm fall, followed by a winter with temperatures close to average. NOAA and other groups will continue monitoring ENSO and Pacific Ocean sea surface temperatures closely through the remainder of 2026.