It's the most sensitive ride in terms of weather in all the parks. Even the slightest bit of rain can shut it down sometimes. Usually if it's just weather related they may let people stay in line. It's why I generally get a FP for it, especially if I go in the summer, because odds are good that it may be converted to an anytime FP if I don't get to ride it during my FP time. (Plus it's generally the hardest of the tier 1 rides to get same day, I've had zero issues getting FEA or Soarin as a 4th+ FP, but TT can be harder at times)