How do you set off fireworks in the rain?
With a portfire, the same as you would in the dry.
It depends on where you are. Different states, counties, and cities can have their own regulations about whether or not fireworks can be set off at all without a special permit, when and where they may be set off, restrictions on the type of fireworks, and so forth. The best solution if you're not sure would be to call your local police department and ask.