Powerlifters squat a little differently than Olympic-style weightlifters. The wider stance, lower bar placement, and shallower squat means they go through a smaller range of motion (ROM). Because the ROM is shorter, you may be able to lift more weight than you have been.
For today's squats, wear shoes with hard, flat soles. If you need to, bust out those tattered Chuck Taylors.
Once you're done with your squats, you should feel warmed-up and ready to try for some heavy-ass deadlift triples.