Forecasters are nearly certain an El Niño winter is approaching and that could mean a big shift in what's expected for weather conditions.
Even in the Midwest.
According to the National Weather Service's Climate Prediction Center, there is a "greater than 95% chance" that an El Niño continues through the Northern Hemisphere winter. The chance of a "strong" El Niño also climbed from 66% last month to 71% this month.
According to the climate center's ENSO blog, there is a 30% chance the event could be on par with "some of the strongest El Niños since 1950."
Last winter provided a surprising amount of rain and warmer-than-normal temperatures in the Chicago area and the latest forecast could mean a repeat, but forecasters caution that "no two El Niños are alike."
"A strong El Niño does not necessarily equate to strong impacts locally, with the odds of related climate anomalies often lower than the chances of El Niño itself," the NWS reports.
What is an El Niño?
Local
El Niño refers to a time in which sea-surface temperatures in the Pacific Ocean, particularly near the equator, are unusually warm, according to Dr. Jim Angel, a state climatologist in Illinois. It is the opposite of a La Niña.
"These (increased water temperatures) change the weather patterns over the Pacific Ocean, which in turn changes the weather patterns for much of the rest of the world," Angel said.
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According to the NWS, "during normal conditions in the Pacific ocean, trade winds blow west along the equator, taking warm water from South America towards Asia." Thanks to a process called "upwelling," however, cold water rises from the bottom of the ocean to replace the warm water. But an El Niño causes the trade winds to weaken and the warm water is then pushed back east.
What does an El Niño do to weather conditions?
Typically, an El Niño year can mean parts of the northern U.S. and Canada are drier and warmer than usual, but the Gulf Coast and Southeast can see wetter-than-normal conditions, along with an increased risk of flooding.
What about the Chicago area?
Typically for Illinois, an El Niño event's impact varies depending on its size, intensity, and duration, Angel said.
"As a result, the impacts can vary from one event to the next. In addition, there may be other factors that influence Illinois weather during these events," Angel said.
In general, some of the impacts could include:
- Summers tend to be slightly cooler and wetter than average
- Falls tend to be wetter and cooler than average
- Winters tend to be warmer and drier
- Springs tend to be drier than average
- Snowfall tends to be below average
- Heating degree days tend to be below average, which means lower heating bills.
Forecasts for the coming winter in the Chicago area are suggesting that residents could experience warmer-than-normal temperatures, with below-normal precipitation.
During meteorological winter, which takes place between Dec. 1, 2023 and Feb. 29, 2024, the CPC says its projections are “leaning above” in terms of average temperatures in the Chicago area and the entire upper Midwest.
Those same projections are “leaning below” for precipitation level during that time.
Those projections currently hold into March as well, according to NWS officials.
Such a development would be in line with how El Niño events typically unfold. During those instances, Illinois and the Chicago area typically see warmer temperatures and below-normal precipitation, especially in the fall and winter months, according to researchers at the University of Illinois.
