Whenever the weather looks a bit iffy you generally put on more fuel and at the same time ask your operations department where they would prefer you to end up, before you depart. But when it comes time to divert, reality sometimes gets in the way. Like a couple of 747 diversions using all the local buses, ramps being fuel due to previous diversions etc. So generally what happens is if you don't have direct contact with your company in the air (ACARS, satellite phone etc.) you call your handling agent and get them to call your company in your behalf. But with an emergency you go wherever you need to and tell your company after the event, if they don't already know.