That is so true. Often when I have to wait for a bus in cold weather and it's raining, which would normally be just annoying, the situation becomes somewhat epic when Rex Regi Rebellis starts to play in my earphones: "Cold autumn rain..."
Also last summer when I saw Turisas in Myötätuulirock festival, it was raining heavily through the whole gig. For some reason it didn't matter at all, almost the opposite! In my opinion, bright sunlight doesn't suit the gory battleground atmosphere nearly as well as good old rain and mud