Why Does The Lake Effect Cause So Much Snowfall?

If you’ve spent any time at all around the Great Lakes, then you’ve undoubtedly come across the term “lake-effect snow” during the winter months. But what exactly is it, and how does it affect the weather around the region?

Walk into this next winter fully equipped with the knowledge and understanding of this strange weather pattern, and learn how to predict what the weather will be like in any given place around the Great Lakes.

What is the lake effect?

Lake-effects, bay-effects or ocean-effects are unique winter weather patterns that appear around large bodies of water, and not necessarily just fresh water, either. Lake-effect weather is common anywhere from the Great Salt Lake in Utah to the Black Sea in Turkey to the Kamchatka Peninsula in Russia, as well as many other large lakes around the world. 

What does this weather look like? Well, if you’ve ever watched a live weather map where meteorologists are talking about lake-effect snow, you’ll see that there are characteristic bands of snow and cold weather that extend out from the lakes. These look different from typical snow patterns that usually appear as clusters, so the areas affected by lake-effect snow are usually referred to as snow belts due to their unique weather conditions. This also means that different areas around any given lake could potentially experience very different effects, depending on where in the snowbelt they are. Around the Great Lakes, these snowbelts are usually to the east of the lakes.

Essentially, large bodies of water can affect the weather around it, causing higher-than-usual precipitation that occurs in those thin bands stretching away from the lake. This could mean downpours of rain during fall and spring months or heaps of snow during the winter, but almost all lake-effect weather occurs in cooler months. 

Let’s break it down.

What causes lake-effect snow?

Precipitation (rain, snow, hail etc.) is caused when warm, moist air rises and cools into clouds. Those clouds grow as they collect more heat and moisture, and eventually the moisture cools enough to condense and fall to the Earth as precipitation. In winter, this precipitation usually falls as snow if the air around it is cold enough. 

Now, the interesting thing about the Great Lakes is that they are large (they are called Great Lakes for a reason) enough to contain a considerable amount of heat. That’s why it takes so much longer for large lakes to freeze over than it does for small ponds, and why the lake effect only works with large bodies of water. 

This is how weather works across the board, but the lake-effect is named so because it’s the presence of water that creates the snow, and that snow appears along the direction of the wind stream that carries it. The result? Thin bands of snow that stretch out from a lake.

This means that one region along a lake could experience sunshine all day long, while another town a few miles away could be covered in snow. The amount of snow any given area receives is dependent on a few factors: fetch, wind direction and temperature difference.

Fetch & wind direction

Lake-effect snow is formed by cold air moving over warm water, so the longer the cold air moves over that warm air, the greater the precipitation will be down the line. 

Fetch, then, is the distance that a mass of air travels over a body of water. Wind direction is closely related to fetch, as the direction from which the cold air arrives can determine the amount of fetch that air receives. 

Because the Great Lakes are fairly unevenly shaped, different areas could receive varying amounts of snowfall, depending on the wind direction, the fetch and the orientation of the lake.

Temperature difference

The next big factor in creating lake-effect weather is the difference in temperature between the land and the water. And since the land’s temperature affects the air temperature, the seasons play a large role in the creation of storms. 

Between March and August, the average temperature of the land is warmer than that of the water, so the lakes do not affect the weather nearly as much. From August to March, though, the average temperature of the land is colder than the water, which is why the lake-effect only occurs in colder months. 

The greater the difference in temperature between the water and the cold air, the greater the storm that forms. That’s why colder months see the greatest snow storms, as the temperature differences can reach nearly 50 degrees (Fahrenheit) in the northern lakes, and nearly 40 degrees in the southern lakes. 

Interestingly enough, if the air gets cold enough for lakes to freeze over, then there is no more warm, moist air for snow storms! Lake Erie, which is only 201 feet deep, freezes over completely and effectively halts any lake-effect weather until it's warm enough for the lake to melt. Lake Ontario, though, is almost four times as deep, so it never gets cold enough to freeze over completely, and the lake effect continues throughout winter. 

Barometric pressure also plays into this, as lower pressure allows that warm, moist air to rise higher into the atmosphere than it would have otherwise. There are a lot of factors that play into that, too, but that’s for another time. 

So, next time you’re watching an approaching winter storm from your cozy luxury Chicago apartment, you can confidently pull up the weather maps on your phone and figure out exactly what those dark, ominous clouds will mean for your day. 

Good luck!

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Featured photo courtesy Unsplash/Adam Chang