I did once internal transfer--promotion.

I didn't like my last position and waited for more than one year to move on to a higher position. I didn't talk to anybody about my unhappiness. Once the new position was posted, decided to talk to my director before I dropped the application. Because of my corp.'s hr policy, once I dropped an application, hr is going to contact my current boss to get reference. I didn't want him to get shocked by the news from hr. What good reference can he gave if he were upset about my leaving ? I wanted to get his support. He was upset at the first a few minutes of our meeting. Because of the hr policy about internal transferring. he was not able to hold me back. At the end of meeting, he totally accepted my reasons and agreed to give me a good reference. HR later told me he gave me a great reference. My advice for you, keep a good relationship with your lead and coworkers and be honest with your lead. You don't want to make him feel betrayed and talk bad about you when Hr or other lead contacts him. I don't recommend you to say anything before you are ready to jump on any new opportunity.