I rode the express bus in the rain several times last week. They shut it down if there is lightning. Just like the outdoor rides. If lightning strikes within 6 miles of the park, all the outdoor rides shut down for 20 minutes, as does the express bus service. If it's just raining it will be running. If the service goes down while you are in route, you will be dropped off outside the gate of your destination where all the other buses drop off. This happened to us once, which was frustrating, but not the end of the world.