How does Lake Michigan affect the weather in Milwaukee?

There's no doubt Lake Michigan is a big part of the city of Milwaukee ? and that's especially true when it comes to the weather.

You can thank the lake for late-fall windstorms, cool summer breezes and dense spring fog. And while its easy to assume if you live by a big lake that you'll probably have a lot of lake-effect snow. But that’s not actually the case here.

Here are the ways Lake Michigan affects whether you reach for a coat, bust out your shovel or turn on your fog lights.

The Great Lakes' 'gale season' brings storms and big waves

The gales of November are most popularly known for causing the waves that sank the S.S. Edmund Fitzgerald and were memorialized in Gordon Lightfoot’s hit song.

But the gales of November happen here in Milwaukee, too.

A gale is a strong sustained wind between 39 and 55 miles per hour. While “gale season” in the Great Lakes runs from September to January, November is the common time for long-lasting wind storms.

The lakes are still relatively warm at this time, said Steve Vavrus, Wisconsin state climatologist. So, when a low pressure system brings cold air from Canada, the lakes become a heat source that energize and strengthen storms, he said.

Strong winds and storms are a big reason why fall is one of the best times to go surfing – yes, surfing – on Lake Michigan.

Lake-effect snow is rare in Milwaukee

Yes, lake-effect snow can happen here in Milwaukee. But it’s pretty rare compared to other cities across the Great Lakes.

For lake-effect snow to happen cold air needs to travel across warm water. A cold, dry air mass will soak up moisture and heat from the lakes like a sponge. The larger the temperature difference between the air and water, the heavier the snowfall. The magic number is at least a 23 degree temperature difference between the water and air at 5,000 feet.

Another important factor is the fetch – or the distance that wind travels over water. The longer the fetch, the more time there is to suck up warm water along the way. And depending on the wind direction, these air masses can spend a lot of time over open water.

When the moist, warmed air finally hits land, it cools and dumps heavy snow.

These events typically happen in the late fall and early winter when the lakes are ice-free and the water is still warm, relatively speaking. Ice acts as a barrier preventing the air mass from soaking up moisture.

Because the jet stream typically moves from west to east, the eastern side of the Great Lakes are especially susceptible to lake-effect snow. This is why New York cities like Buffalo, which sits on Lake Erie, and Rochester, which sits on Lake Ontario, often make headlines for their heavy lake-effect snow events. Michigan's Upper Peninsula, on the eastern shores of Lake Superior, is also known for heavy snowfall.

While the ingredients, like cold air and warm water, are there in Milwaukee, the wind direction usually isn’t, Vavrus said. The weather pattern has to come from the northeast for Milwaukee to experience a lake-effect snow event.

But it's unclear how climate change will impact this weather event. Vavrus said a warmer climate may cause fewer cold, dry air masses coming down from Canada, which generate lake-effect snow events. On the other hand, climate change is leading to less ice cover on the lakes, giving more time for the relatively warm lakes to come into contact with cold air during the winter, he said, favoring more storms.

More: Great Lakes records fourth lowest ice cover in 50 years. How will that continue to impact us?

Lake Michigan brings fog to Milwaukee in spring

Thick fog often rolls into the city in the spring, obscuring the view of the city’s iconic places like Hoan Bridge and American Family Field.

The dense fog is the springtime version of lake-effect snow – except the exact opposite.

Lake-effect snow happens when cold, dry air moves over the still-warm Lake Michigan. Springtime fog occurs when wet, moist air moves over the cold lake surface.

When the warm, wet air passes over, the air condenses and forms fog.

Why is it cooler by the lake?

Lake Michigan is the Cream City’s air conditioner, which can help make your summer patio tour of the city a lot more comfortable.

The lake is much slower to warm up than the land in the spring and early summer. That’s why in early summer the temperature in Milwaukee can be dramatically lower than nearby Madison.

On hot summer days later in the summer, the temperature difference between the water and land can create a local wind flow blowing cooler air off Lake Michigan further inland, Vavrus said. This cooling effect is especially pronounced when the wind is blowing from the east or northeast, he said.

The lake breeze can be very localized. Vavrus said that sometimes the lake breeze can only be felt halfway through Milwaukee. Other times, it can be felt in counties further inland.

Typically, the larger the temperature difference between the water and land, the stronger the breeze will be and the further inland it will go, he said.

More: Many Milwaukeeans live in a heat island, and 'we can't air condition our way out of this'

Changes in Lake Michigan water levels alter the shoreline

Like your bank account Lake Michigan has a budget – a water budget that is.

There are processes that add water to the lake and others that take it away. These things don’t always come out the same, and that’s why lake levels are always changing.

For instance, runoff and precipitation add water to the lake. Evaporation and water diversions take water out of the lake.

Lake levels fluctuate daily, seasonally and over longer time periods.

Water levels tend to be higher in the spring, and often peaking in the summer. Melting snow and spring rains increase runoff into the lake, and because the lake is cooler than the air there is less evaporation. Water levels decline in the fall and reach their lowest point in the winter. This is when evaporation is the highest because the water is warmer than the air.

Great Lakes water levels have fluctuated more dramatically over the past two decades, reaching historic highs and lows within a matter of a few years. These changes are driven by climate change, altering the components that make up the lakes’ water budget.

Since 1950, precipitation has increased by 17% across Wisconsin, with the biggest increases occurring in the southeastern part of the state.

The past decade has been the wettest. Besides dramatic fluctuations in water levels in shorter periods of time, there will likely be an overall increase in Lake Michigan’s water levels; one study suggested this could be upwards of 17 inches.

More: What's the state of the Great Lakes? Successful cleanups tempered by new threats from climate change

Caitlin Looby is a Report for America corps member who writes about the environment and the Great Lakes. Reach her at [email protected] or follow her on X @caitlooby.

This article originally appeared on Milwaukee Journal Sentinel: What is the lake effect in Milwaukee?