Winter precipitation in Milwaukee vs Chicago

Dear Tom,
Milwaukee’s lakefront is about 80 miles north of Chicago’s, yet I’ve noticed that during a winter storm rain falls in the Loop while downtown Milwaukee gets heavy snow. Why does this happen?
Christopher Ricco, Northbrook
Dear Christopher,
There might be several reasons. Often the rain vs. snow demarcation line lies between the two cities, and being farther north, Milwaukee gets the snow. During late-autumn snows, northeast winds blowing onshore off the still relatively warm lake may provide enough warmth to bring rain to the Loop, while the water off of Milwaukee, being a bit colder, allows for snow. Other factors would be stronger vertical motion and drier low-level air in the Milwaukee area, both factors which would tilt the precipitation type toward snow.

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