It really is cooler near the lake

I recently received a letter from somebody living in South Milwaukee complaining that forecasters use the term "cooler near the lake" too much. The wind isn't always from the east, they wrote, and we dramatize the lakeside/inland difference. And this complaint came from somebody who has lived in South Milwaukee for over 50 years! Have they checked a map lately? Or have they taken a dip in Lake Michigan in the spring?

As frustrating as it might be for those living lakeside, Lake Michigan keeps things well refrigerated this time of year. The lake water temperature hovers between 35 and 42 degrees, and breezes tend to blow off the lake on many spring days. The lake is a huge source of fresh water and also a source of local weather changes. It creates its own mini-circulation, alternating between lake breeze and land breeze. Those changes in wind direction can send the thermometer fluctuating wildly.

Riding along Lake Drive with the windows rolled down in April and May can be quite an adventure. On many days the air varies between comfortably warm to downright chilly depending upon the distance between the road and the lakeshore.

Because of the large temperature difference between land and water, a lake breeze usually begins around mid to late-morning on many spring days. The warm spring sun heats the ground, causing the air to rise. As warm air rises upward, cool air over the lake rushes in to take its place.

So, lakeside locations typically warm up quickly on a calm, quiet spring morning, only to chill back down again once the lake breeze kicks in. Once the sun sets, the land begins to cool off quickly, dropping the air temperature down close to the value of the lake water temperature. When air over the land and lake are approximately equal in temperature, the lake breeze stops.

Overnight the air over land often gets colder than air over the lake, and a gentle breeze blows from the land back out over the lake. This is the land breeze.

The large lake-land temperature difference is related to the large heat capacity of water. Water gains and loses cold or warmth slowly. In spring, Lake Michigan is holding a lot of cold water stored over from the cold air of winter. It will take several months for this large body of water to lose this chill and warm up. Even on a hot June afternoon, the lake retains leftover chill from the cold season.

Try the following experiment to see water's heat/cold storage ability, Take a glass of water and place it in the refrigerator for a couple of hours. Do the same for an empty glass.

Now that they are both chilled, take the glasses and place them on the windowsill in full sunshine. After 15 minutes check the water temperature by dipping your finger into the water. Then feel the outside of the empty glass to check on its temperature. You will likely find the water temperature takes quite a while to warm up compared to the temperature of the outside of the empty glass.

Before you start feeling sorry for people living close to the lake in spring, remember the relief they feel during the summer heat of July and August. When the thermometer reaches 90 degrees in Waukesha, Whitefish Bay and Cudahy are staying cool with temperatures in the mid 60s. And that is the time when Lake Michigan truly is a GREAT lake!


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