With Lake Michigan looking more like the Arctic and Loyola being buried in snow, an otherwise warm winter was abruptly broken up in late January and early February by three weeks of nonstop snow and ice.
While the snow is now melting and area residents are no longer digging themselves out of their street parking, the questions still remain as to what caused this cold snap and what the potential effects are.
Rick DiMaio, instructor at Loyola’s School of Environmental Sustainability and a former meteorologist, said the cold snap Chicago and other parts of the country experienced was due to the polar vortex. This is a system of cold air and low pressure that hovers around both the North and South Poles, according to the National Weather Service (NWS).
In the United States, this cold air is contained by the polar jet stream, a narrow band of high winds that runs east to west and is often a boundary between warm and cold air, according to NWS. This boundary normally sits at 50-60 degrees latitude but varies, meaning if the jet stream pushes south, Chicago at 41 degrees latitude could experience colder weather.
DiMaio said Chicago and the northern United States experienced colder than normal temperatures in February because the jet stream sat in Southern Texas for three weeks. While this happens every year, DiMaio said it’s more noticeable because recently, there have been longer periods of warm weather and milder winters overall.
“When you get longer streaks of warmer weather, the polar vortex becomes more noticeable,” DiMaio said. “If it starts getting cold in the middle of December, people are okay with that. But all of a sudden, when you have two and a half months of really, really warm weather, and then you get super cold and super snowy, everybody freaks out about it.”
In November 2020, at the start of winter, 0.7 inches of snow fell in Chicago — slightly below the 1.2 inches Chicago normally gets in November, according to NWS. December saw even less snow, with only 0.2 inches recorded. This is well below the normal 8.2 inches of snow Chicago typically experiences in December and is in the bottom five for snowiest Decembers on record.
This mild winter ended in January when 21.9 inches of snow fell in Chicago. This was double what Chicago normally gets in January and was the 10th snowiest January on record, according to NWS. NWS also indicated almost all the snow in January hit in the later part of the month with most hitting between Jan. 26 and Jan. 31.
February also saw higher than normal amounts of snow. NWS preliminary reports state Chicago received 21.6 inches of snow — the 8th snowiest February on record — and 12.5 inches above the 9.1 inches Chicago normally gets in February.
DiMaio said this weather is an indirect result of climate change. A changing climate is leading to months of warm weather followed by three weeks of really cold weather, DiMaio said.
“To put it into perspective, our winters are becoming more extreme, but they’re becoming less cold,” DiMaio said. “However, when they do get cold, they get really cold and really snowy for a short period of time.”
Among the most striking images from the recent cold snap were the tundra-like ice sheets forming on Lake Michigan and rolling icy waves giving the city an Arctic-like appearance.
DiMaio said Lake Michigan freezing over is normal but what’s not normal is how long it took for this to happen.
“What’s interesting about this year is it took a really long time to ice up,” DiMaio said. “We went from 10 percent ice coverage on the Great Lakes on Jan. 28, to 40 percent ice coverage on all the Great Lakes on Feb. 17.”
Areas of Lake Michigan normally start seeing ice coverage above 10 percent in late December or January, according to data from the National Oceanic and Atmospheric Administration (NOAA). However, in recent years, ice cover charts have shown ice cover starting later in the year.
Despite the cold blast, DiMaio said he doesn’t expect any more winter weather this year on the scale previously seen.
“I would not be surprised if we don’t have another major snowstorm for the next two weeks, and we’re definitely done with the cold arctic air,” DiMaio said. “During this past cold spell, we had five days where it hit zero or below. And that’s going to be it for the rest of the year. I don’t see us getting back below zero.”
In order to keep the streets safe, snow plows and salt spreaders are used to clear snow and melt ice. This winter, the city of Chicago maintained 280 snow removal routes, covering 9,400 miles of roadways, according to the Department of Streets and Sanitation.
But dumping salt onto roadways isn’t without consequence. DiMaio said most of the salt will end up in Lake Michigan as a result of runoff, but the environmental impact is unclear due to seemingly more rainfall in the spring.
“It’s unclear whether or not an increase in salt is impacting the environment because of the fact that we’ve had such wet springs,” DiMaio said. “The wet springs tend to offset the runoff of salt into the rivers and the lakes.”
DiMaio also said the massive amounts of snow combined with temperature swings and overuse of salt may lead to road issues.
“You generally tend to get a lot of potholes,” DiMaio said. “So the streets are going to be in really, really awful shape.”