Did you know a little sprinkle of rain in the air well taking a helicopter ride is unlike to be seen on the window screen as the main rotors powerful force simply brushes the rain away.
You will be flying in light, reasonable rain flow as it will not effect the helicopter at all. If the light rain brings high winds then its really the wind that will cancel your flight.
Downpours along with high winds results in little visibility so will sure ground all helicopters as instructed by law.
If you arrive at the helicopter centre with a little rain in the air don't despair, its highly likely the flight will still go ahead.