If you are having a problem describing a rainy dark night or any other, just pop outside and into the real scenario and simply tell dramatically what you are seeing ensuring you exaggerate and spice it. Avoid telling what it is, just describe it intensely that the reader will know what is it.
Many books tell how to write books but they never tell you how you can practically train yourself to describe scenarios. So going around taking some videos will help to get started.
You can practice here and leave your description of the night in the comments section.