OK, I did some research -- tell me if this is right:
Say Groudon and Kyogre switch in the same turn. Whichever Pokemon is slower, is the Pokemon whose weather ability takes precedence. So if Kyogre is slower, it's Drizzle; if Groudon, it's Drought.
Then the prevailing weather ability lasts the entire time its Pokemon is in play, or for five turns after its Pokemon is defeated/switched out, UNLESS:
A) Another weather move is activiated, such as Rain Dance, Sunny Day, etc
OR
B) Groudon or Kyogre switches out and is switched back in, their weather ability taking over when they switch in
Correct? For Uber-tier battles, it seems Reshiram and Groudon would work well together, the latter using Drought to halve Water damage to itself, boosting Reshiram's Blue Flare, and allowing both to wield one-turn Solarbeams...