Why does Aurora often have the lowest temps in the Chicago area?

Dear Tom,
I have noticed that the temperature at Aurora is often the lowest in the Chicago area. Why is this the case?

Jamie Miller,
Aurora

Dear Jamie,
Your question comes up occasionally. Aurora’s chilly nighttime temperatures, sometimes colder by several degrees, are a source of puzzlement, especially to Aurora residents whose thermometers do not register such low readings. Those cool temperature readings are the result of the location of the thermometer. The thermometer is accurate and it is checked regularly. It is located at the far west end of the rural Aurora Airport in Sugar Grove, about 10 miles from downtown Aurora. Located in a low-lying setting, it is susceptible to radiational cooling. On calm nights, chilly, dense air settles into that low spot. The thermometer is located there to support airport aviation operations and its readings are not intended for other purposes.