I used to get those a lot, but after I switched phase convertors and ran only one machine on each one they have gone away. I don't know if that helps but I would look at your power equalizing switching on the RPC to make sure it is keeping things with in 5% power flux. I burned up a FANUC control on my Takisawa lathe trying to run both my haas and lathe on one RPC. Life has been much better since I put them on seperate RPCs with good load switching. It could be as you say the funky weather affecting your power but you can ask your power company to hook up a power recorder to isolate where the trouble is. This is an area where there can be a lot of finger pointing but you need to isolate the problem quickly.
Hope things smooth out.