This happened quite a while back, but I just remembered it and thought I would ask about this.

I came out of Folgunthur late one day and noticed a dragon circling Solitude. It did not come down and attack me, nor did it fly away. It just was circling Castle Dour. Later I stopped by someplace else close to Solitude and noticed a dragon still circling there. Finally, having forgotten about the dragon I fast travelled to Solitude some time much later and instantly got attacked by a dragon.

I am curious if anyone else has seen this. (Do not include the 3 named dragons that Alduin raises during the MQ.) Do you have any idea when that dragon might have spawned? Was it just there waiting to pounce on me when I next went to Solitude? I was under the impression that random encounters spawned when you entered a cell. I did not think they would be in the cell already so that when you entered they would attack you.