I've had to shoot in all kinds of weather, come rain or shine so the first thing you should do is make sure you've discussed the possibility of rain during your consultation. Your supplier should always suggest ideas for if the weather turns sour and have a backup plan, which will usually revert to photographing the wedding party indoors. Choose a venue which has lots of outside cover, that way everyone can keep dry, and there are plenty of opportunities to get some great shots. If you're hell-bent on having your photographs outdoors and there's no cover, I would order lots of brollies, just in case. Your photographer should be able to orchestrate some funny and quirky shots of you and your guests braving the weather. On a more serious note, if it does happen to rain, sleet or snow on your wedding day, then this can be an absolute Godsend for any photographer that knows how to create portraits by using flash to light up the scene. December nights move in fast, so if the weather turns and you think it's all over, think again. Don't miss out on this opportunity and make sure you're confident that your suppliers can produce some epic shots.