This is the idea I almost posted up yesterday. I'll post the reason against it after.
Relative weather settings for each track. They all have default states (warm/dry for FE, cold/moist for BL, etc) and the Master Server periodically changes state. For instance, "+50% wet" would make it heavy rain at BL but light at FE. "+50% wind" could create a tornado at FE but just moderate winds at BL. "+50% fog" could make zero visibility on a naturally misty track, and reduce view distance on the others. A bit rough, but you get the idea.
Day and night settings would be run independantly with maybe a 3 or 4 hour rotation (and obviously it wouldn't be night at the same time on FE, KY and BL because they're so far apart).
The biggest problem I could see with this idea yesterday was that it would have the same issues as a global weather/time setting. If it was wet, it would be wet on every server using the sync system. If you didn't want to drive in the rain/snow/fog you'd be pretty much SOL. And if too many servers chose not to use it for this reason, it'd be as well not existing.