The newest version to be released on sunday of the news mod ia v0.95b seems to be addressing this issue. The modder said that rain probability is set to be 15% in the upcoming version.
I kinda like the rainy races. But I haven't had too many yet so I'm actually quite OK with the way things are set in the game. Anyway, I remember quite a number of wet races this season. Possibly more than the average season?