The south and east of the Great Lakes is famous for the huge amounts of snow it receives. When the snow starts to fall every year, people start discussing the phrase “lake-effect snow”. Lake-effect snow which is influenced by the movement of cold air over the relatively warm water of the Great Lakes often comes in late autumn and early winter. Because of the at least 20 degrees’ difference between the lake water and the overrunning air, it’s easy to form huge amounts of snow. As the cool air crosses the water of Great Lakes, the lowest levels of the atmosphere begin to warm and pick up moisture. This newly warmed atmosphere is lighter than the cold air above it, so it starts rising. As the changed air continues to climb higher and higher, it finally meets much colder atmosphere which changes the moisture into water drops and ice, forming clouds. After this course repeats a number of times, the clouds become heavier and heavier, and then they are changed into snow and fall down. The most important point that decides the amount of snowfall is the direction of the wind. If the wind runs perpendicularly（垂直地）across the lake, there won’t be plenty of time for clouds to develop. However, if the wind runs in the opposite direction, clouds will form easily. The longer the cold air travels over the lake, the more moisture it is able to produce, which leads to a greater amount of snow. The largest amount of the lake-effect snow was found across the U.P. of Michigan, the northwestern Pennsylvania and the far southwestern and northwestern New York, which are all along the south or east of the Great Lakes. It has been over 100 inches of snowfall in a winter season. 小题1:The level of the snowfall depends on ________.
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