What is Lake-effect Snow, and Why Study It?

If you live near the Great Lakes, and especially in upstate New York, you will have most likely heard of lake-effect snow before. But elsewhere, the term is probably foreign to your ears. So what is lake-effect snow? And what is so special about it? I personally think it is a very cool weather phenomenon, although the general process behind it are relatively simple.

Lake-effect snow is simply snow that forms over a lake (in our case, Lake Ontario in the Great Lakes) due to the difference between the temperature of the lake surface and the air directly above it. Lake-effect snow occurs at large lakes all over the world, but is perhaps most prominent over the North American Great Lakes. In late autumn or early winter, before the lakes freeze over, very cold airmasses from Canada will occasionally swing down over the Great Lakes, bringing frigid temperatures to the region. The air might be 10-20 degrees Fahrenheit, while the lake water temperature might still be 40-50 degrees. This creates a situation where the lake water is much, much warmer than the air flowing over it.

Most of us know that warm air rises as long as it is warmer than the air around it. As the cold air flows over the much warmer lakes, the air in contact with the water will warm due to conduction and will also pick up lots of moisture from the lake itself. This creates a layer of relatively warm, humid air right above the water which eventually begins to rise through the cold, dry air around it. Just like with summertime thunderstorms, this rising warm air eventually cools off to the point that condensation can occur, forming a cloud, and eventually snow. If the warm air is rising fast enough, and contains enough moisture, then the snow that forms in the cloud can become very heavy in a very short period of time. This is illustrated in the photo below.