Unfortunately yes, fair weather is required especially during training where you will want to be concentrating on learning to control the aeroplane before having to deal with the techniques required for different types of weather. In general the conditions required for training are;
- Wind speed no more than 13mph
- Visibility greater than 5 Km in flight
- Cloud base above 1000 feet
- Preferably no rain, though it is quite possible to fly in light rain it is a very miserable experience in an open cockpit.
In short the weather required for flight to be enjoyable and worthwhile for training is about the same as you would want for an enjoyable walk in the countryside.