Chicago experiences a hot-summer humid continental climate, with four distinct seasons shaped by its location along Lake Michigan. Summers are typically hot and humid, with July daily averages around 75.4 °F (24.1 °C) and afternoon highs peaking at 84.5 °F (29.2 °C). Heat waves are common, with temperatures reaching 90 °F (32 °C) on an average of 17 days per summer. Lake breezes can moderate the temperature in waterfront neighborhoods, providing some relief during the hottest days.

Winters in Chicago are cold and snowy, with average highs around 36 °F (2 °C) from December through March. January and February are the coldest months, with record lows reaching −27 °F (−33 °C), as seen during the 1985 cold snap. Snowfall can persist into April, and blizzards occasionally impact the region, such as the winter of 2011. The city also experiences urban heat island effects, making city areas slightly milder than surrounding rural regions, particularly at night and in winter.

Spring and autumn are generally mild and brief, characterized by lower humidity. Dew points in summer typically range from 55.8 °F (13.2 °C) in June to 61.7 °F (16.5 °C) in July, occasionally climbing to nearly 80 °F (27 °C) during heat waves. Chicago lies within USDA plant hardiness zone 6a, transitioning to 5b in suburban areas. Rainfall is mainly delivered by thunderstorms, averaging 38 per year, and the city is susceptible to severe storms that can produce hail, damaging winds, and occasionally tornadoes. Notable tornado events include the F4 Oak Lawn tornado of 1967 and the F3 tornado that struck downtown Chicago in 1876.

Lake Michigan plays a key role in moderating Chicago’s climate. Waterfront neighborhoods are slightly cooler in summer and less bitterly cold in winter than inland areas. Lake-effect snow and polar winds can influence temperature and precipitation patterns, creating microclimates across the metropolitan region. Chicago’s proximity to the lake, combined with its urban environment, produces a unique blend of continental extremes and local moderation, contributing to the city’s distinctive seasonal character.