Use
however if you want to contradict or contrast with what was said before. Example:
- He makes a lot of money. However, he is very stingy.
Use
provided to indicate a contingency or condition.
- Provided that there is enough money, we will eat out Thursday night.
Use
in the event of to indicate a contingency or condition. Example:
- In the event of rain we will stay inside.
Whether is often used to indicate a contingency or possibility. Example:
- I don't know whether he has left the building or not.
:)