On the first sunny spring day of May, you leave your house in shorts and a T-shirt and head toward the lake for a waterfront stroll. But then you arrive lakeside, step out of your car and immediately realize that your outfit is not remotely appropriate. It’s freezing. Somewhere between home and lake, spring was left behind.
If you wonder what exactly is ruining your day, it’s something we informally call the lake effect.
This buzzkill is the lakeside cooling and cold breeze felt most noticeably from late spring to early summer, explains Tim Halbach, the warning coordination meteorologist with the National Weather Service office in Sullivan.
Here’s why it happens. In the winter, as you’ve probably noticed, everything around here gets extremely cold, including Lake Michigan. When spring hits and temperatures rise, the land we walk on starts to warm up, as does the air above it. That happens to the water in the lake, too, except way … way … slower. “Water holds heat much, much longer than land,” says Mark Baden, chief meteorologist for WISN-TV. Its temperature doesn’t increase or decrease anywhere near as quickly as the land’s.
That is because the “specific heat capacity” of water is higher than land, which means that it takes a lot more energy to heat it. The freeze of winter will linger in that water for months, cooling the air above it long after the springtime warmth has generated enough energy to warm the land. The effect reverses in winter, when the water holds the summer warmth and causes shoreline snowstorms when cold air from the land passes over it.
The reason the spring lake effect forces you to grab a jacket even on terra firma is thermodynamics, which Halbach describes in simple terms: “Cold air wants to go toward warm air.” The chill over the lake circulates toward the warm air over the land, cooling everything down along the lakeshore, especially on calm days without strong winds to push the cool air back east. Halbach says this effect can be felt as far as two or three counties away from the lake.
And the effect can be dramatic, Baden says: as much as 25 degrees between Waukesha and Downtown Milwaukee on some days – meaning that a shorts-and-t-shirt day inland could be sweater weather closer to the lake.
At least Wisconsin only has one coastline. It can get really complicated in places like Florida that experience the effect from both the east and west, causing a convergence of ocean breezes that can lead to sudden afternoon rain and thunderstorms.
Thankfully, Baden has some good news for the 2020 lake effect. “The lake is 4 to 5 degrees warmer than average this year,” he says. “So spring should be easier on us.”