Weather in dreams is generally a detail that may be left unanalyzed unless it is particularly noticeable to the dreamer for some reason. Rain is one of these notable exceptions. The reason comes from the relationship between water and fertility that many cultures affirm. In dreams where rain and water-fertility are identified, there is usually an unique feature to the rain. This can be as mundane as a drought that is broken to rain that only falls indoors on one or two particular people.
Does the rain cause you problems of some sort or is it a welcome addition to the scene?