The updated version of the data that site uses is
here instead of ending in 1980, the newer data is through 2000. The dates given there are based on a 10% chance of a 32 degree or lower night after that date. daves garden has a function where you put in your zip, and get dates for each 10% for 24, 28 and 32 degrees, that match with this, though I haven't found their source. In some cases, you may not be able to wait for that 90% sure it won't freeze date, for example, here, it's a month from 50% sure (april 3) to 90% sure(may 2), most plant at what turns out to be the 30% sure date, in the middle of the 2, april 15.
This site has some of the same data in graphical form. I can see there for example, that if I waited until May 2, I'm 90% sure of not getting a frost, but the average high is already up to 80, 2 months later, when I'd expect to start getting tomatoes, it's getting to the peak of summer and the average highs are in the upper 90s.
Here it doesn't seem to be as bad as I read people post about in Texas and Florida though, I'm thinking the dry air helps the plants cool themselves, and fruit sets through all but the worst of summer.
I still haven't figured out how we got powdery mildew on the squash so bad last year though, without much rain or humidity, and drip irrigation.