Will Illinois see a ‘super’ El Niño pattern? What it means for metro-east weather
The National Weather Service reports an El Niño pattern is likely to emerge this year, but the potential effects in southwest Illinois are a little different from those to the West Coast or South.
The terms El Niño and La Niña refer to climate patterns determined by tradewinds and water temperatures. El Niño occurs when tradewinds are weakened and warm water is pushed east, the National Oceanic and Atmospheric Administration reports, while La Niña has the opposite effect.
“Those impacts are much more prevalent in other parts of the Northern Hemisphere. In the middle part of our continent, it’s a little less clear,” Mark Fuchs, senior service hydrologist with the NWS St. Louis office, told the News-Democrat in a recent interview.
The term “super” El Niño is informal and does not appear in the official NWS forecast, but has been popularly used by some media outlets because the forecast calls for the possibility the expected El Niño pattern could be strong.
“If El Niño forms, the potential strength remains very uncertain, with a 1-in-3 chance it would be ‘strong’ during October-December 2026,” the NWS forecast reads.
We’ve been in a La Niña pattern since September, and it’s now starting to diminish. A transition from La Niña to an ENSO-neutral state is expected in the next month, the NWS reported March 12, and the neutral state is favored from May to July. El Niño has a 62% chance of emerging sometime between June and August, and is expected to last through at least the end of the year, the forecast reads.
“The best correlation between El Niño and La Niña is during the winter months,” Fuchs said.
The primary effect a potential El Niño pattern would have on the weather in the metro-east and across Illinois would be an increased likelihood of a drier-than-usual winter, according to Fuchs.
“That’s not to say it can’t be wet or we can’t have a winter of record snowfall during an El Niño winter, it’s just not common,” Fuchs said.
An ENSO-neutral state occurs roughly 40 to 50% of the time, Fuchs said, and episodes of La Niña and El Niño typically last nine to 12 months, but can persist for years.
“El Niño and La Niña events occur every two to seven years, on average, but they don’t occur on a regular schedule. Generally, El Niño occurs more frequently than La Niña,” the National Oceanic and Atmospheric Administration reports.
Any significant effects of an El Niño pattern likely wouldn’t be seen locally until the winter. The climate pattern doesn’t tend to bring strong indications of warmer- or colder-than-usual weather for Southwest Illinois, but does tip the scale toward a dry season.
What about spring & summer weather in Illinois?
The NWS Climate Prediction Center’s three-month seasonal outlook reports the metro-east has a 40 to 50% chance of above-normal temperatures from April through June, with equal chances of below- or above-normal precipitation.
Typical temperatures in Belleville range from about 46 to 71 degrees Fahrenheit in April, 56 to 79 degrees in May, 65 to 87 degrees in June and 68 to 90 degrees in July, according to NOAA data from 1991 to 2020.
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