Climate of Chicago - Lake Breeze

Lake Breeze

Chicago experiences microclimatic effects because of relative chillier waters of Lake Michigan, these effects are most pronounced during spring and early summer. Very often a local lakeshore breeze pulls much cooler, moist air into Chicago than the usual hot air of the Plains States (usually a moist air mass depending on upper level circulation), but the effect may be so localized that only the immediate waterfront neighborhoods (especially northern lakeside communities) are cooler than inland parts of the city. South and southwestern suburbs are sometimes 20 °F (11 °C) or more warmer under these conditions. The lake breeze also has other effects, including dense fog spilling into the city. Because of the closed-loop circulation pattern with a lake breeze that moves back and forth across the city, it is thought to significantly increase low-level ozone counts. Differing wind direction on either side of the thermal dividing line allows for sharp updrafts under certain conditions, favorable to thunderstorm development. Offshore or land breezes shutdown the lake breeze and can have the opposite effect, with over lake convection occurring, usually in mid-late summer and fall. As a general rule, winter temperatures are warmer along the lakeshore and downtown than inland, but the lake can increase storm intensity.