Apologies if this has already been covered. I've found that if it rains midway through a race, making the track wet, if I then restart the race the weather in the sky will revert to the beginning of it's script, but the track conditions will remain wet. The track is still dynamic, as the cars still dry it fairly quickly, but it's happened everytime I've tested it.
dont know if it is a bug or made intentionaly but I like it. it makes race conditions less predictable and more realistic.
I guess it could be by design.... However if you want to run a race with particular weather e.g wet for 1st half, dry for 2nd half but you crash say halfway through and have to restart, the track conditions/weather appear to carry on from where they got up to upon restarting. This means that the restarted race would be dry weather for the duration, but with a wet track in the opening laps.
restarting race, as well as restarting whole event make marbles on BL remain. So even if rain/wet restarted, BL still changes racing conditions. I suppose you are asking for solution for situations which may happen occasionally. Since that, what about reloading track? Reloading track restarts all conditions. Then you may set grid, weights and go on. Unfortunately in current version reloading track wipes out also marbles/BL. But I believe loading some track state will be possible in future.
It might be, that "restart race" means exactly how you'd see a restart procedure in real life. That means, the race will be restarted but weather conditions stay as they are. Probably, reloading track or the whole weekend should also reset weather conditions.
I find that sometimes I want to restart the session with the track going back to its 'raw' state but unfortunately only way is to exit & then reload the track.