Night photography is some of my favorite and I've recently begun to incorporate it into weddings. I got so many questions about how I did the photo above.
The illuminated clouds were pure luck. There were storms and lighting in the distance which gave the clouds great definition. Here is another example of the same setup, just taken at a different location and a little later in the evening.
The thing that is difficult with taking these shots later in the evening is that the camera struggles to focus. My camera was searching and searching to focus for the shot above. Last and most important, be careful no one looks at the flash directly when it fires!