Warm winter: Experts weigh in on what’s causing unseasonable temps, what to expect

Spring plants have been pushing through the ground for weeks because of our mild winter. Here, these daylilies have been in bloom for a few weeks.

The Chicago area is closing out its warmest February ever, and the signs are clear: Trees are leafing out, once-dormant plants are peeking up through the ground, and pollen counts are going up.

Tuesday’s weather swung wildly, with temperatures in the 70s during the day followed by storms and tornado warnings at night. Although temperatures were to dip into the more typical 20s and 30s Wednesday, springlike weather is forecast to return by the weekend.

We talked to weather and plant experts to find out what’s driving the mild conditions and how they could affect the region.

What’s causing this year’s mild winter?

Weather officials have said the unseasonably warm temperatures can be chalked up to a combination of a few things, including long-term global warming trends and the current seasonal climate pattern in the Pacific Ocean, El Niño, which typically portends drier and warmer winters.

“The magnitude of how mild this winter has been is surprising, but this is pretty consistent with the long-term trends and the fact that we’re in an El Niño,” state climatologist Trent Ford said.

How warm has this winter been compared with others?

This season is likely to break into Chicago’s top five warmest winters, Trent said. With meteorological spring beginning March 1, however, there still are a few days left for the final numbers to get tallied.

The National Weather Service on Wednesday declared this February “as the warmest February on record for both Chicago and Rockford,” noting that Chicago missed its all-time record daily high for February and meteorological winter by 1 degree Tuesday.

Zachary Yack, a meteorologist with the National Weather Service in Chicago, said the office currently is predicting a monthly average temperature of 39.4 degrees, which would break February 1882′s average of 39 degrees.

Last year, despite being in a La Niña, Chicago logged its 14th warmest winter on record.

“La Niña tends to bring us a bit of a colder winter, and last year was not that,” Yack said. “You don’t want to attribute it all to climate change, but warming trends make it more likely we have these milder winters despite having patterns in the Pacific that would otherwise make us a bit on the cool side.”

What does mild winter mean for gardeners?

This month’s roller coaster of weather has been confusing for plants and gardeners alike, with “spring racing ahead,” Ford said, adding that he’s gotten reports of silver maples blooming across the Chicago region, tulip bulbs popping up and grass in parts of southern Illinois starting to go green.

The big concern here is that if plants break dormancy too early in response to warm temperatures, they’re at risk for damage when freezing conditions come back around. This is especially a worry for farmers in the southern part of the state raising crops such as peaches, apples and cherries.

Sharon Yiesla, a plant knowledge specialist with the Morton Arboretum, said she’s been getting calls from residents wondering whether they can start their spring gardening tasks such clearing away leaves and pruning.

Her advice? Take the weather day by day.

“Every day is going to be a different experience. We’re dealing with some very strange things,” Yiesla said. “We kind of need to learn to stop looking at the calendar and look at what’s going on around us in terms of weather and in terms of what stage of development the plant is in.”

For those worried about their emerging bulbs or perennial leaves running into freeze damage, Yiesla said don’t panic: The plants are meant to come out early and can tolerate the cold.

If frost is in the forecast, gardeners can cover their plants with mulch or leaves and remove the layer once the danger has passed.

What does a mild winter mean for allergies?

Allergy sufferers may have noticed an increase in symptoms last year due to the mild winter, and this year has a similar fate in store.

In fact, experts said climate change is lengthening the pollen season and making allergies worse.

At Loyola Medicine, the official allergy count won’t start for weeks, but Rachna Shah recently ran a pollen test after hearing from allergy patients and found abnormally high pollen numbers for February, with moderate pollen level from trees and low levels of mold.

Some trees began budding as early as December, Shah said in a news release.

What can we expect over the next few weeks?

The seemingly unpredictable weather is expected to continue as we head into March, with no distinct pattern on the horizon, Yack said.

“We probably will see some systems here and there that may drive things cooler or drive things warmer,” he said. “We’re kind of in that period of back and forth.”

• Jenny Whidden is a climate change and environment writer working with the Daily Herald through a partnership with Report For America supported by The Nature Conservancy. To help support her work with a tax-deductible donation, visit

Jenny Whidden – Daily Herald Media Group

Jenny Whidden covers climate change and the environment for the Daily Herald