page_title: Chicago
section_title: Climate
hierarchical_section_title: Chicago / Geography / Climate
caption_attribution_description: English: Steam Rising from Chicago River
context_page_description: Chicago, officially the City of Chicago, is the most populous city in the U.S. state of Illinois, and the third-most-populous city in the United States. With an estimated population of 2,693,976 in 2019, it is also the most populous city in the Midwestern United States. Chicago is the county seat of Cook County, the second-most-populous county in the US, with a small portion of the northwest side of the city extending into DuPage County near O'Hare Airport. Chicago is the principal city of the Chicago metropolitan area, often referred to as Chicagoland. At nearly 10 million people, the metropolitan area is the third most populous in the United States.
  Located on the shores of freshwater Lake Michigan, Chicago was incorporated as a city in 1837 near a portage between the Great Lakes and the Mississippi River watershed and grew rapidly in the mid-19th century. After the Great Chicago Fire of 1871, which destroyed several square miles and left more than 100,000 homeless, the city made a concerted effort to rebuild.
context_section_description: The city lies within the typical hot-summer humid continental climate (Köppen: Dfa), and experiences four distinct seasons. Summers are hot and humid, with frequent heat waves. The July daily average temperature is 75.9 °F (24.4 °C), with afternoon temperatures peaking at 85.0 °F (29.4 °C). In a normal summer, temperatures reach at least 90 °F (32 °C) on as many as 23 days, with lakefront locations staying cooler when winds blow off the lake. Winters are cold and snowy, although the city typically sees less snow and rain in winter than that experienced in the eastern Great Lakes region; blizzards do occur, as in 2011. There are many sunny but cold days in winter. The normal winter high from December through March is about 36 °F (2 °C), with January and February being the coldest months; a polar vortex in January 2019 nearly broke the city's cold record of −27 °F (−33 °C), which was set on January 20, 1985. Spring and autumn are mild, short seasons, typically with low humidity. Dew point temperatures in the summer range from an average of 55.7 °F (13.2 °C) in June to 61.7 °F (16.5 °C) in July, but can reach nearly 80 °F (27 °C), such as during the July 2019 heat wave. The city lies within USDA plant hardiness zone 6a, transitioning to 5b in the suburbs.
  According to the National Weather Service, Chicago's highest official temperature reading of 105 °F (41 °C) was recorded on July 24, 1934, although Midway Airport reached 109 °F (43 °C) one day prior and recorded a heat index of 125 °F (52 °C) during the 1995 heatwave. The lowest official temperature of −27 °F (−33 °C) was recorded on January 20, 1985, at O'Hare Airport. Most of the city's rainfall is brought by thunderstorms, averaging 38 a year. The region is also prone to severe thunderstorms during the spring and summer which can produce large hail, damaging winds, and occasionally tornadoes. Like other major cities, Chicago experiences an urban heat island, making the city and its suburbs milder than surrounding rural areas, especially at night and in winter. The proximity to Lake Michigan tends to keep the Chicago lakefront somewhat cooler in summer and less brutally cold in winter than inland parts of the city and suburbs away from the lake. Northeast winds from wintertime cyclones departing south of the region sometimes bring the city lake-effect snow.
caption: Downtown Chicago and the Chicago River in January 2014
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