Ask Tom Why: Chicago weather without Lake Michigan

May 25, 2010

Dear Tom,

What would Chicago's weather and climate be like without Lake Michigan?

—Jeff Kozinski, Mokena

Dear Jeff,

Without Lake Michigan on Chicago's eastern doorstep, the city would have a far more continental climate characterized by warmer days, colder nights and a greater daily temperature range. The loss of cooling lake breezes would bring a more uniform temperature distribution across the metropolitan area in spring and summer. Overall there would be a decrease in cloudiness and lower annual precipitation total with the loss of lake-effect snow and rain, lake breeze-generated thunderstorms and the fact that rain-generating frontal boundaries would no longer stall at the south end of the lake. Late fall storms would bring more snow to the city as the northeast winds accompanying them would not carry warm air from 50-degree lake waters inland.