Ric hit the nail on the head. In bowling regionals in the past, I tended to see the same scenario every time: On the Friday night practice session, the lanes always seemed to hook more then I would expect for the pattern. It usually played easier then I was expecting too. On Saturday, the pattern seemed heavier with less hook, and it was a little tougher then the night before. If you make it to Sunday, the pattern plays exactly like I would expect it to at that point. It hooks less then previous days and plays as tough as I would expect a PBA pattern to play. The reason for this scenario is the underlying house pattern memory fades with time as the lanes are stripped and the PBA pattern is put out more and more.
The other factor is the topography of the lanes themselves. In our center we have relatively new synthetic lanes. One pair in particular was not put in correctly. The outside boards on the right are sloped to the right slightly. That makes it rather difficult to play Cheetah on this pair as you are fighting gravity to go "uphill" from the outside line. We also see the first phenomenon as well, as this house usually places a lot of oil outside five on their house shot, so when we play Cheetah, the tapes look correct, but we do not have the dry bump on the last few boards as the memory of the house shot is there.
