Chicago-area residents might feel like it’s been a really long winter after enduring stretches of below-normal temperatures in January and February and a couple snowfalls in March. But the lingering cold snaps actually contributed to a proper winter — unlike the record highs and bitter but brief Arctic blasts of recent years.
“You look at the numbers — whether it be for Chicago, for Illinois, for the Great Lakes — and it was sort of an unremarkable winter,” said Trent Ford, the Illinois state climatologist. “But it felt like it was intense because we’re getting these types of winters, as far as temperatures are concerned, so much less frequently.
“At one point in late February, I was like: My god, it’s been cold forever. I’m so tired of this,” he said.
Last winter, atmospheric temperatures in the area averaged 34.9 degrees, which was 6.8 degrees above normal, according to the National Weather Service. February 2024 was the warmest in Chicago and Illinois in nearly 150 years, and overall it was the city’s fifth warmest winter on record. It tracked with last year being the hottest year on record globally, with 15 straight months of record-breaking temperatures from June 2023 through August 2024, according to NASA.
But the cold, seemingly normal winter this year doesn’t disprove longer-term warming trends from human activity and heat-trapping greenhouse gases. In fact, despite the persistent winter temperatures, ice cover on Lake Michigan and snowfall in Illinois were below average likely due to an abnormally warm, dry beginning to the season.
Ice cover on four of the Great Lakes remained mostly below long-term averages. Ford said the core, coldest months of the season were bookended by a mild December and a warm start to the spring, making it harder for ice to concentrate over the lakes.
Seasonal snowfall across portions of the Upper Midwest remained 2 or more feet below average. Dry weather meant Chicago saw just under a foot of snow — less than half the normal amount.
“It was cold enough, but we just didn’t get the right features in the right place to consistently get a lot of snowfall,” Ford said.
Dry weather from the fall and a lack of precipitation this season have also led to relatively low water levels in the Great Lakes, even though they are generally at their lowest in the winter. For instance, lakes Michigan and Huron — which hydrologists consider one lake because they are connected at the Straits of Mackinac — were almost 8 inches below normal levels in February, according to a monthly report from the Detroit District of the U.S. Army Corps of Engineers.
That is the lowest they have been since 2014, according to the International Joint Commission, a binational organization between Canada and the United States that manages the shared waterways. Drought conditions also accelerated the drop in water levels in two of the other Great Lakes to below their long-term monthly averages — levels were at their lowest in Lake Superior since 2013 and Lake Ontario since 2003.
Lower lake levels can affect shoreline ecosystems and commerce, specifically shipping routes. Research suggests ships can lose up to $30,000 a trip because of the lighter loads they’re forced to carry in low water conditions.
Across the Great Lakes, ecosystems rely on ice during the winter. Without it, shorelines are unprotected from storm surges and large waves, which can cause coastal erosion. With less ice, the Great Lakes can absorb sunlight faster, which drives surface warming. Warmer waters can accelerate fish spawning and have ripple effects across food webs, in turn affecting commercial fishing. And many communities have economic ties to seasonal ice fishing and outdoor sports that require a thick and solid surface.
According to National Oceanic and Atmospheric Administration data, ice concentrations peaked on the lakes around Feb. 20-21, when just over half of their total surface froze. On average, the lakes experience a combined maximum of 53% ice cover sometime in late February or early March, with as much as 91% of the lakes covered during the highest years. This year, only Lake Erie had a mostly above-normal season with ice cover between 80% and 95% after an Arctic blast in mid-January.
For Lake Michigan, a February peak represented little more than a third of its surface. However, last year, maximum ice cover was only 16% in a historically low season for ice across all the Great Lakes.
Still, “it was much better than last year,” Ford said. But the ice didn’t remain long because the water underneath was not cold enough.
He called it “thermal inertia” — big bodies of water cool more slowly than the atmosphere, so warm fall and December temperatures make it so the lakes take longer to catch up to sudden drops in temperature in January and February. Last year, the surface temperature of Lake Michigan in November was the warmest since recordkeeping began 30 years ago.
“The lake is responding to longer timescales than a season or a month,” Ford said.
Freelancer Vivian La contributed.
