If the weather forecast is well above limits and two completely separate suitable runways are available what's wrong with planning that as your diversion runway, and adding a bit of holding fuel on top?
The problem is that the intended airport may close for reasons other than weather. Security situations, accidents, fires, ATC or NAV/COM issues, natural disasters, etc.
So it's a good idea to always have enough fuel to reach an alternate airport, plus reserves, even if not required by regulations.