my dad doesn't like me smoking weed, but he knows there's nothing he can do except call the police, which he won't. I think your dad is a good dad, but needs to understand weed more open mindedly. In my opinion he is concerned cause of all the brainwashing propaganda given to people in your country. The letter is good, I hope it does open his eyes. But also try and confront him and sit down and talk to him.

Hope it helps