It was 86 yesterday.
Opened the 2nd weekend in May, was going to open the last weekend in April but it snowed the weekend prior, then it the outside temp got really hot and stayed that way (that's IL for you, we go straight from winter to summer and vice versa). Opened up to clear pool that was about 75, threw on my new and first solar cover, cut it to fit, and cranked on the heater to bring up to 84 and then shut it off (hope not to use the heater again until late Sep or early Oct to extend pool season). It has remained mid to high 80s since then, I now swear by the solar cover.