My rendition following the Planet Photoshop tutorial: http://www.planetphotoshop.com/nuclear-photo-effects.html
The original cloud picture came from a Google image search of storm clouds.
I added a couple of variations: Smart filter for editing the radial blur and a PWL layer to darken the sky and clouds around the perimeter.

forum discussion: http://forums.dpreview.com/forums/read.asp?forum=1006&message=39313051