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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.
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