Chicago Weather

As El Niño impacts world, here's how it could impact winter for the Chicago area

While an El Niño winter will likely mean shifts in the forecast for the Chicago area, forecasters say "no two El Niños are alike"

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For the first time in four years, forecasters with the NOAA's Climate Prediction Center say that El Niño will impact winter, but what will that mean for the Chicago area and winter weather?

While an El Niño winter generally causes significant changes in the forecast for the Chicago area, 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.

Here's a look at what to expect:

What is an El Niño?

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.

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?

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.

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.

What is the latest prediction?

According to the NOAA’s seasonal temperature outlook, which were released on Thursday, forecasters say they are “leaning” toward a warmer-than-normal winter for most of Illinois and Indiana. The confidence level grows for areas near Lake Michigan, with forecasters saying temperatures will “likely” be above normal for the winter months.

Most of the Midwest and the northern U.S. will see above-average temperatures, with the greatest confidence that the Pacific Northwest and New England will see warm temperatures.

In terms of precipitation, most of Illinois is expected to have roughly normal snowfall amounts this winter, but nearly all of Indiana, as well as far-eastern Illinois, is projected to have below-average amounts of precipitation during the winter.

The southern United States is expected to see wetter-than-normal conditions, in line with previous El Nino events.

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