Ovulation Temperature Dip?

I'm new to charting, so please excuse my lack of knowledge. Yesterday I got a positive OPK in the early morning on Clearblue Advanced Digital. I don't ever have much CM, but I did have slight twinges and cramps all day yesterday. I expected to see a temperature rise today, but instead it dipped significantly. My question is: is it common for temps to dip on the day of ovulation? Thanks for your help.