Weather Blog

El Niño Likely This Fall and Winter

On Thursday, the Climate Prediction Center issued an El Niño Watch for the upcoming fall and winter Seasons. 

After experiencing a weak to moderate La Niña this past winter, sea surface temperatures have been steadily rising across the eastern Pacific. The El Niño Southern Oscillation is currently in a neutral phase but is expected to transition into a weak El Niño by early Fall and possibly strengthening into a moderate El Niño by the 2018-2019 winter season. 

What is El Niño?

El Niño is the positive phase of the El Niño Southern Oscillation (ENSO), a variable climate pattern that is determined by monitoring sea surface temperatures across the central and eastern Pacific Ocean. When sea surface temperatures are and remain above average, then ENSO is in a positive phase or El Niño, whereas cooler than average temperatures mean that ENSO is in a La Niña phase. 

Why is it Important?

While it's just one of many different climate patterns that can influence seasonal weather pattern, the phase of ENSO can have a significant impact on U.S. weather conditions during the fall and winter seasons. For instance, we were in the midst of a moderate La Niña during the 2017-2018 fall and winter season. This undoubtedly helped Central Illinois see colder and snowier conditions through early 2018. Being able to identify which phase of the El Niño Southern Oscillation we will be in can give us a glimpse of what kind of winter season we may have.

How Does El Niño Impact Central Illinois?

All El Niño events are different and can vary significantly depending on its strength. You'll notice that weak and moderate El Niños historically brought near to below average temperatures to Central Illinois while strong El Niños brought above average temperatures. As for precipitation, there is some variability across the country depending on the strength of El Niño. However, we've historically seen drier than normal during weak and moderate El Niños and near to slightly above average moisture during stronger episodes. 

Overall, El Niño climate patterns often bring warmer and drier conditions to Central Illinois during the winter. Warmer sea surface temperatures across the eastern Pacific Ocean leads to more convection and storm systems streaming into the southern U.S. This means southern and western parts of the U.S. often see cooler and wetter conditions. El Niño conditions also tend to lead to less active Atlantic hurricane seasons due to increased wind shear thanks to a stronger sub-tropical jet stream.

It's too early to know what kind of weather Central Illinois will have this upcoming winter. However, knowing that an El Niño is likely to be in place, we can lean towards a drier and potentially warmer winter season. Other factors such as the Arctic Oscillation, the North Atlantic Oscillation and the Eastern Pacific Oscillation are just a few of the teleconnections that will also have an impact on this upcoming winter season but their impacts are not clear at this time.  

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