Well, it stormed at my house all day yesterday and I can see WDW from here . . .
May is a transitional month when it comes to weather. In the winter and spring, rain is tied to weather fronts. That is what happened yesterday. A cold front slowly passed through the area, and the rain associated with the front moved slowly as well. In the summer, we get mostly storms tied to the sea breeze collisions, so they are in the afternoon or early evening for the most part, and quickly come and go. May is sandwiched in between, so sometimes we get a day or two of rain because of a front passing through, and sometimes it gets hot enough for the sea breezes to kick in and produce an afternoon storm.
As most people have said, 12 days out the forecasts are very unreliable. I wouldn't count on any forecast more than three days out, and even those can be subject to change at a moments notice. It is very rare to have rain all day, every day, for several days in a row. I can only recall that happening in the winter if a front just gets stuck over us and doesn't move.