You can find out, if you were born in the USA and aren't older than say, me or J-Walk. Here's the weather for St. Louis on August 18, 1965, for example. For other locations, just enter the four-letter airport code, which just adds a "K" to the three-letter airport code you are familiar with. So O'Hare is KORD instead of the ORD you're used to seeing. The O'Hare weather records only go back to 1958, but other airports can go back to 1940 or so. More weather history data here.