DEKALB, Ill. — Northern Illinois and the entire Midwest could be facing a warmer, drier winter, thanks to a patch of warm water near the equator.
But there is no need for snow lovers to panic — or for summer lovers to break out the patio furniture.
Victor Gensini, associate professor of meteorology at Northern Illinois University in DeKalb, said that even though the El Niño weather pattern could influence winter toward a warmer trend, snow and cold still will make an appearance.
“Are we going to have cold spells? You bet. Are we going to have snow and cold shots of air from Canada? Absolutely,” he said.
El Niño, also known as ENSO, or El Niño Southern Oscillation, is a climate pattern due to warmer waters in the equatorial Pacific Ocean, off the coasts of Ecuador and Peru. Those warmer waters influence the jet stream over North America.
“The reason we look at ENSO and this El Niño, when you have an El Niño, your jet streams typically go on steroids. When you have a lot of warm water there, you get a lot of thunderstorm activity,” Gensini said.
“That thunderstorm activity juices up the jet stream and you get a very strong, fast, subtropical jet stream, in the northern hemisphere.”
The U.S. Midwest plunged straight into what Gensini described as a strong El Niño, from three years of La Niña, in which the waters of the equatorial Pacific Ocean are colder than normal.
In the Midwest, La Niña winters tend to bring more snow and colder temperatures. El Niño winters in the Midwest tend to bring more moisture and temperatures that trend warmer.
The last strong El Niño was in 2016, and before that, the winter of 1997-1998 was the last strong El Niño winter.
“When we have El Niños, we typically get a little more mild here in the Midwest. Mild can mean a few things. It can mean warmer, with less snow, but you still get the same amount of precipitation, just more of it falls as liquid instead of solid. You get more rain instead of snow. That is the biggest thing for our area,” Gensini said.
He said that while El Niño may get the headlines, other factors influence winter weather across the Midwest and in northern Illinois.
“There are other things that can happen. It’s not just El Niño. El Niño is kind of the loudest instrument in the orchestra, but it’s only one of the instruments in the orchestra,” he said.
Gensini said that forecasters use El Niño and weather records from El Niño years to get a general picture of what the winter ahead may be.
“Even though we are in an El Niño and we would expect a warmer winter, not every single El Niño in the database did produce mild conditions. It’s just that a vast majority of them do,” he said.
“If you were wanting to know what this winter would look like across the Midwest, you would err on the side of a more mild winter, just based on the historical precedent.”