I did Fast School last year. It was freakin awesome. You're gonna have a blast!! Absolutely POURED rain all morning the first day, and to be quite honest I am kinda glad that it did. It really showed me how much grip motorcycles have in wet conditions and makes me feel alot more at ease when I get cought in the rain (light or heavy) moving on forward. The tires on the bikes they have there are sport street tires, not slicks....now if they have slicks, that would be a different story and we wouldn't be on the track. It's way too far away from the dates and the weather will probably change about 5 times or so haha.
Either way, if it does rain, don't worry about it, you will have a blast. Just watch out for turn 1 as there was a pretty large puddle there. Someone was blasting 130km or so around turn 1, hit the puddle (his line was off because I think he was focussing on puddle) and ate schit! Turn 5 is pretty tight too and someone infront of me also laid it down. With having said that, people were crashing in the dry conditions too. Just be smooth on the throttle and you will be fine