Did you notice steam or smoke coming off of Lake Michigan and Chicago River waters Monday? You weren't alone.
That phenomenon has stunned viewers repeatedly during Chicago winters and again this week as temperatures stay well-below zero degrees and water temperatures remain above freezing.
So what led to that steam show?
According to the University of Maine, the “steam” is actually water vapor. That vapor forms when “really cold air moves over relatively warmer water and the thin boundary layer of warm air just above the surface.”
When the evaporating droplets rise, the cold air can only hold a limited amount of moisture, forcing the liquid to condense into fog, according to the university.
According to Mental Floss, a similar process occurs when you breath in cold weather, because the tiny droplets of water in your exhaled breath condense into liquid water and ice, creating the “steam” that you see in front of you.
While the air temperature in Chicago on Sunday was downright frigid, with some areas seeing lows of 10 degrees below zero, the water in Lake Michigan remains comparatively warm, with a recorded temperature of 39 degrees in the Chicago Crib and 34 degrees at the shoreline, according to the National Weather Service.
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That massive disparity in temperature between air and water led to the appearance of steam on the lake.
Eventually, the warm air barrier between the water and air will dip below 32 degrees, and the result will be the formation of ice on the lake’s surface.
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With temperatures expected to remain on the cold side, that ice will likely begin forming this week, meaning that the “steam” will no longer be present.
