The lists of Chicago's record daily high and low temperatures always show only one date for each record. Why aren't ties included?
The National Weather Service's National Climatic Data Center in Asheville, N.C., archives the country's weather and climatic data, including daily temperature records. The center's publications list the most recent occurrences of record temperatures, but, in the case of multiple dates, a “+” sign will appear next to the tied entry indicating that other unlisted dates of occurrence do exist.
Meteorologist Mark Ratzer says the computer system at the Chicago Weather Forecast Office also lists the most recent occurrence of a record temperature. The advantage is that it indicates how recently records have occurred.