Spectacular crepuscular rays, and an approaching rain shower!
Crepuscular rays or "God rays" are sunbeams that originate when the sun is just below the horizon, during twilight hours. Crepuscular rays are noticeable when the contrast between light and dark is most obvious. Crepuscular comes from the Latin word "crepusculum", meaning twilight. [Wiki]
You can see a random selection of my photos here at Flickriver:
www.flickriver.com/photos/9815422@N06/random/