Snapedom

The scene where Severus Snape met Albus Dumbledore on a windswept hill in order to bring him news of Voldemort's decision to target Harry and his family clearly took place before Severus Snape took up his position as a teacher at Hogwarts (or why would they need to meet outside the school or its grounds?), and may have been their first face-to-face encounter in quite a while. Neither of them trusted the other: Dumbledore's first move was to disarm Severus, while the latter begged for his life. Dumbledore believed Severus was bringing him a message from Voldemort. This encounter was one of the significant events in the line connecting Trelawney's prophecy to Voldemort's first fall on October 31st 1981. When did it take place?

I'm posting it this way because I still don't get journal cuts, apparently. I'd prefer the comments, if any, to be on Snapedom, to keep discussion in one place.