The high for Saturday in Provo is 90°.
Luckily -- BYU Football: It's Not in the Afternoon Anymore™
The BYU Cougars host Boise State with Saturday night kickoff of 8:15 p.m. MT, which will create a perfect atmosphere for some September football under the lights. I'm sure BYU is quite fine with this after suffering through mid-90s, ~50% humidity for the entirety of its game at Nebraska last week.
Sunset should happen at 7:42 p.m., which will finally pull the temperature below 80°. However, tailgaters should be advised of the hot forecast and plan accordingly during the day. Most will already have plenty to drink and some shaded, covered areas, but if you plan to hang out for the bulk of the day (late night kicks are perfect for tailgating, giving you all day to enjoy friends and football on TV), see what you can do to pack along extra shade for your friends at the stadium.
At least you'll already be staying a few degrees cooler by WEARING WHITE for the white out game.
It should be a beautiful night for football, with breezes that should be no stronger than around seven miles per hour. Even if the game extends to midnight (it will if it lasts as long as last week's marathon in Lincoln), it should still be warm enough to stay comfortable.
Here's your forecast, courtesy of Weather.com: