My two cents... not all rainy days are alike. I have a friend who has lived all over the world, including several years in Dublin where it rained every day and was usually not warm. She rode in the rain there all the time. Then one day when she was back in the US, she and I did a ride together. It started out hot and sunny, then a big black thunderstorm cloud caught up with us and there was a gust of wind that literally took my breath away and we were pelted by heavy rain for a quite some time. Later my friend said that is doesn't rain like that in Dublin, it's much lighter and is not accompanied by wind and thunder and lightning.
So if your weather is frequent rain but it's not too heavy and does not involve hazards like flooded roads or wind that knocks down trees or lightning, then yes I would say it makes sense to invest in some good rain gear and get out there and ride. But I personally avoid riding when there are hazards like flooded roads or wind that knocks down trees or lightning.
As for what good rain gear entails... hypothermia is a real risk if your clothes are wet and the air temp is not hot. For starters you want a jacket that keeps you dry while cycling in rain -- one that keeps the rain out but is breathable enough to not make you soaked with sweat. A cap or helmet cover or hood for your jacket to keep your head dry and the rain out of your eyes is also good. Gloves, tights, leg warmers, shoe covers etc. as needed to keep you warm. Fenders for your bike to reduce the amount of water that sprays from the road onto you. Waterproof bags to keep food, wallet, phone etc dry.
If there's a good chance it will rain on the day of the charity ride, it will be helpful for you to train the in the rain so you can experiment with different types of clothing to see what keeps you most comfortable.
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles