Lá Fhéile Padraig - why F''h''éile?
why is there the h in Fhéile?
Quoting from this page on lenition:
Because it is never possible that two genitives come after one another, the first is only lenited and remains in the nominative ("functional genitive")(gender irrespective): e.g. obair bhean an tí = housewife's work, Lá Fheile Pádraig = St.Patrick's Day (lit. "Day of the Feast of Patrick")