What is the most 90s in a season that started this late?

Dear Tom,
We had to wait until June 28 for our first official 90, but now the heat seems locked in. What is the most 90s in a season that started this late?
Adrian G. Deerfield
Dear Adrian,
We had Chicago weather historian Frank Wachowski check the archives and since 1871 the city has had 33 other seasons with the first official 90 on, or after June 28. The vast majority of these occurred prior to 1943, years when the city’s official thermometer was located near Lake Michigan. Since the city’s official temperature site was moved inland, only four years, 1958, 1960, 1981 and 2000 logged the first 90-degree day this late and the average number of days for those years was 10. The greatest number of 90s in any of those 33 years was 18 in 1900. After the first 90 on July 2, there were six more in July, 10 in August and one in September.

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