How the Windy City Became Pea Soup City

Foggy and cool, Chicago felt more like San Francisco this June. From the view below, the Sears, er, Willis Tower looked on many occasions as if had been cut in half by fog. And the likely reason for this soupy scene? The polar vortex. Yep, the weather pattern that froze Midwesterners in their tracks earlier this year is now delaying summer’s start.

Chicago is now what the Chicago Tribune is calling a “battleground” between northern and southern air currents. The result: a dispiriting spring full of fog and rain.

The jet stream—a high-altitude current that flows like a meandering river in the atmosphere—acts as boundary between cold, dry air in the north and warm, humid air in the south, and directs weather systems from west to east. Last winter, that river of wind took a hard turn south into Canada and the United States, bringing with it freezing air (all the way to Atlanta!). Interestingly, a warming Arctic might be contributing to this frigid phenomenon.

Since the polar vortex rolled through in January, the Great Lakes haven't warmed up at their usual rate (their ice cover didn’t melt until May!). In fact, the water is still pretty chilly. So when warm, easterly winds blow across the unusually cool Lake Michigan, damp air and fog blanket the city. According to theTribune, the National Weather Service reports fog and low cloud cover to be four times what it is normal this time of year.

[[{"type":"media","view_mode":"media_original","fid":"579614","attributes":{"alt":"","class":"media-image media-image-right","height":"55","style":"width: 228px; height: 55px; float: right; margin-left: 3px; margin-right: 3px;","typeof":"foaf:Image","width":"228"}}]]Oh, and grab your scarves on the way to the lakeshore, because every once in a while, the region gets a “pneumonia front.” That’s when temperatures along the lake can drop 16 degrees in just about an hour. Pneumonia fronts are rare, but when they do blow in, they can spark thunderstorms—a more suitable summer staple.

“Will we see these patterns more often in the future? The answer is I don’t know,” says Ed Hopkins, a climatologist with the Wisconsin State Climatology Office. While global warming may prime the atmosphere for wacky weather, it’s still hard to pinpoint the cause for a single weather event, or even a pattern. The jury’s also still out on whether there is a causal link between global warming and a shifting jet stream, though recent research does suggest a connection between the two.

And that just may mean a foggy future for the Windy City.

Originally published by OnEarth.