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

The Chicago area is closing out what could be 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. Though temperatures were to dip into the more typical 20s and 30s Wednesday, springlike weather is forecast to return by the weekend. We talk 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 say 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 to others?

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

The same goes for February’s record. This month is on track to become our warmest February on record, but that is subject to change given Tuesday evening’s cold front that will last through Wednesday.

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

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. 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,” Trent said, adding he’s gotten reports that silver maples are blooming across the Chicago region, tulip bulbs are popping up and grass in parts of southern Illinois is starting to go green.

The big concern here is 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 like 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 to not panic: The plants are meant to come out early and can tolerate the cold.

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

What does 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 say climate change is lengthening 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. Shah 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 press 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, see dailyherald.com/rfa.