How do I know when Ovulation is close?

I have three normal adult females that I have witnessed lock over a dozen times with each of my males. This has been going on since late november, now I know it can take up to 6 months for a female to take the sperm but are there any tell tale signs besides the "glow"? I've tried palpating but have been failing miserably. So I'm sorta in the dark. Any hints, advice, or criticism is welcome! Thank you

http://www.ballpython.ca/gallery/breeding.html

Here's the best step by step I can think of...good luck!

Ahh cool seeking, then the glow. That makes sense, I cant wait!