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How much of Lake Michigan has to freeze over before the lake-effect snow machine gets turned off?

Dear Tom,
LaPorte has been getting hammered with lake-effect snow this year. How much of Lake Michigan has to freeze over before the lake-effect snow machine gets turned off?
— Chris Manning, LaPorte, Ind.
Dear Chris,
Lake-effect snows end when a lake freezes over, because a totally frozen lake becomes nothing more than ice- and snow-covered ground. Lake-effect snow develops when cold air passes over the warmer lake waters, allowing moisture to evaporate and condense into clouds and snow. When a lake ices over, evaporation ceases, and clouds and snow will not develop. Lake-effect snow in Buffalo, N.Y., usually shuts down in mid- or late winter, if ice coverage on Lake Erie exceeds about 80 percent. While Lake Michigan has never completely frozen over, lake-effect snow dramatically decreases when the arctic air passes over portions of the lake with high ice coverage.