I had an situation a couple of days ago. One inbound and one outbound. Both in climb/decent and radar headings to ensure proper separation.
About 10nm prior to the meeting point the inbound told me:
"Approach, AirlineXXX we are turning left heading 280 to avoid". That would be exactly on the outbound's track. There was at the time about 3000' between them.
The STCA immediately went off, and I replied: "NEGATIVE, opposite traffic 2500' below climbing through your level! Right turn to avoid is approved"
He returned to his original track and didn't say anything for a while. After a while he complained about having to fly through a CB giving him moderate turbulence.
The moral:
Tell us about the weather as early as you can. I will shake a h*** of a lot more hitting another aircraft.