The most memorable storm that I remember, was more for its location than for its intensity.
A group of us were touring Dorset, and had camped near Giants Hill, in Cerne Abbas.
At about 11pm one evening, the most wierd electrical storm started up, complete with multicoloured lightning, but no rain or thunder. There were just wierd "fizzing" noises, and a psychadelic light show for about an hour.
In the end, we all (the whole camp site, just like a scene out of "Close Encounters" when the spaceship comes down) just stood there in awed silence, as the opposite hill went from black, to neon blue and then pink, followed by brilliant white.
Just to add to the "pagan" effect, this is what was being illuminated so vividly on Giants Hill, which was directly opposite the camp site.
Then the rain started about an hour later, and most of us Pagans were washed out. I slept in the car, along with two other neanderthals.
Never forgotten it, though........