(The Center Square) – After three La Nina winters in a row, Illinois is shifting to an El Nino winter this year.
Sea surface temperature anomalies in the equatorial region of the Pacific Ocean determine whether or not Illinois will have a La Nina or an El Nino winter, meteorologist Ben Duebelbeiss at the National Weather Service in Lincoln, said.
“During El Nino years, we see temperatures that are warmer than normal. That can shift the jet stream a little further north, especially during the cold season,” Duebelbeiss said.
El Nino is part of the El Nino southern oscillation climate pattern which tracks changes in the temperatures in the central and eastern Pacific Ocean, he said.
“The El Nino is the warm phase and the La Nina is the cold phase,” he said. “We basically oscillate between the two.”
Minor changes in the ocean temperatures – one degree Celsius – affect global weather patterns. So when water temperatures in the equatorial Pacific region change by one degree, that can affect where the jet stream sets up, affecting the weather in the mid-latitudes where Central Illinois is. “When you move around the position of the jet stream, that is going to affect where storms end up tracking over the course of the winter. And it can affect temperatures – how far north the warm air can get or how far south the cold air can spill,” Duebelbeiss said.
El Nino winters can vary from mild to strong. Expect to know more on the third Thursday in October when the National Weather Service’s Climate Prediction Center issues the official winter forecast.
Unofficial indicators point to a winter with slightly warmer temperatures and near to below-average precipitation, Duebelbeiss said. Duebelbeiss makes it clear that seasonal outlooks are averages for the December, January, February time frame.
“We are still going to have a snowstorm or two in there somewhere. And we are still going to have some arctic outbreaks of cold air into the region,” he said. On average, it appears that temperatures will be a little warmer than usual this winter. And it is likely that we will have less snowfall.