In western Pennsylvania, where I live now, we rarely get the climate extremes that would call for cancelling a baseball game.
I have had games cancelled for snow early in the season and have had some cold days, but we have played on....In the summer we have some hot days, but I have never seen a game cancelled for heat....I have had games rescheduled to night games however.....
However when I lived in Texas, I did have games cancelled when the heat index made it beyond responsible to play........but noone ever let it make it to an umpires decision........those were cancelled prior to my authority over the game....