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Dear Tom,
Are other cities as fortunate as Chicago is in having 150 years of weather data to utilize?
Anne Kozak, Clarendon Hills

Dear Anne,
The Chicago National Weather Service, previously known as the Weather Bureau, began operation here, along with 29 other cities, on November 1, 1870 — 153 years ago. Weather observations in the earliest days of the Service were simple compared to the observations of today.

Maximum and minimum temperatures from Nov. 1 through Dec. 31, 1870, were from observations taken at 7am, 4pm and 11pm. From Jan. 1, 1871,  through Sep. 30, 1871, they were determined from observations at 7am, 2pm, 4pm, 9pm and 11pm.

Due to the Chicago Fire of Oct. 8-9, 1871, all original records from Oct. 1-14 were lost. Temperatures at 7am, 4pm and 11pm for the period Oct. 1-8 were obtained from War Department weather maps and at 7am, 2pm and 9pm from Oct 9-14, they were taken from observations from a Smithsonian Institution volunteer observer residing at 55 Clark  Street. These were used to determine the city’s maximum and minimum temperatures.

It was not until June 12, 1872, that maximum and minimum thermometers were used to register high and low temperatures. The readings were not from midnight to midnight, however, because the last observation for the day was at 11pm and the station did not have a thermograph. Midnight to midnight maximum and minimum temperatures began in Chicago in June, 1888, when the station was finally equipped with a thermograph.