If the weather is inclement, we recommend using plastic bags or clingfilm to protect your fireworks from the wet – especially if you are setting up sometime before firing. Cakes, fountains and roman candles will easily fire through a layer of plastic, but we recommend uncovering wheels and rockets before you fire them.
For further information check out our Blog post at https://lovefireworks.co.uk/what-if-it-rains-on-the-night-of-my-fireworks-display/