Lake Effect Snows
Lake Effect Snows
Lake effect snow is a type of unusually heavy snowfall that occurs in the winter when cold air masses warm and moisten as they pass over large, open bodies of water that may still be warmer than the surrounding air. The resulting instability in these air masses forms clouds that drop heavy precipitation in narrow “snowbelts” along downwind shores. Lake effect snows are common downwind of the Great Lakes in the United States and Canada, the Great Salt Lake in Utah, and in parts of Scandinavia, Korea, and Japan.
Human-caused climate change may temporarily increase lake effect snows in some areas due in part to shrinking winter ice cover on big lakes, an increasing tem- perature differential between air and more quickly warming water, and increased humidity as temperatures climb. However, by the end of the twenty-first century, some climate models predict significant decreases in lake effect snowfall totals, with drier conditions and more precipitation falling as rain due to widespread warmer temperatures.
Historical Background and Scientific Foundations
increasing since the 1930s, while areas outside of the Great Lakes snowbelts have shown no particular pattern. This trend is likely due to warmer water and air temperatures. The beginning of the Great Lakes ice season has started increasingly later and ended increasingly earlier since 1850, leaving more water open longer to warm and moisten descending blasts of cold Arctic air, that in turn dump more snow.
Increasing lake effect snowfall is likely to continue as long as winter air temperatures remain cold enough for snow to develop. But climate models for the region predict significant decreases in lake effect snowfall, accompanied by increasing incidences of lake effect rainfall, by the year 2100.
Impacts and Issues
Decreases in lake effect snow in the long run may ensure fewer disruptions in economic activity—which can slow when travel is complicated by snowfall, as well as lessen danger to human life and property. But less snow will likely have harsh impacts on economies that depend on winter recreation. For example, a single dry winter from 1997 to 1998 cost ski resorts downwind of the Great Lakes an estimated $120 million.
WORDS TO KNOW
CLIMATE MODEL: A quantitative way of representing the interactions of the atmosphere, oceans, land surface, and ice. Models can range from relatively simple to quite comprehensive.
PRECIPITATION: Moisture that falls from clouds. Although clouds appear to float in the sky, they are always falling, their water droplets slowly being pulled down by gravity. Because the water droplets are so small and light, it can take 21 days to fall 1,000 ft (300 m) and wind currents can easily interrupt their descent. Liquid water falls as rain or drizzle. All raindrops form around particles of salt or dust. (Some of this dust comes from tiny meteorites and even the tails of comets.) Water or ice droplets stick to these particles, then the drops attract more water and continue getting bigger until they are large enough to fall out of the cloud. Drizzle drops are smaller than raindrops. In many clouds, raindrops actually begin as tiny ice crystals that form when part or all of a cloud is below freezing. As the ice crystals fall inside the cloud, they may collide with water droplets that freeze onto them. The ice crystals continue to grow larger, until large enough to fall from the cloud. They pass through warm air, melt, and fall as raindrops.
Decreases in lake effect snow may also have major implications for certain ecosystems. For example, ecologically and economically important tree species that dominate the snowbelts of Michigan—such as sugar maple, American beech, and Canadian hemlock—may be severely reduced in number by decreases in snowfall, giving way to other species.
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