Whenever it rained at the track on a practice day, I was out there as much as I could.
Still, as a Californian, I would fear rain. I agree with Davin on his comment–for me, it was definitely a mental thing, knowing I had almost zero experience in the wet. Rain racing isn’t hard…you just can’t get greedy, and you have to be ok with being a little sideways here or there.
The biggest thing that helped me I suspect was later on in my career I raced on dirt in Focus Midgets. That for a pavement driver was pretty intimidating at first, but the car control I learned from that was stupendous, and now I want to believe I would be better in the rain, given some practice time.
In terms of coaching, I give the usual tips–run off-line, gradual inputs, and look for standing water on the straights, look where you want to run. However, the really fast guys in the rain are smacking curbs, getting the kart sideways, etc…so I would need more practice to be a good advisor for driving in the rain.
I agree with Davin and Mason–if it’s raining on a practice day, you should get your butt out there! Especially when no one else is doing it, imagine if you practiced even a little bit! You would have a massive advantage in those events. As a racer, I want an unfair advantage…