Storm clouds at dusk over the Common

I've just found this picture which I'm back-blipping. I'd forgotten I'd taken it. The light was amazing with the setting sun's rays only reaching the high storm clouds. I should know what type of clouds they are, but I've forgotten. l love the shapes they make. I'll have to go and find 'The Cloudspotter's Guide', by Gavin Pretor-Pinney, from one of my many piles of books. I haven't seen it for years but I know it isn't far away. 

When I first started blipping I'd sometimes photograph books when inspiration was lacking. I may have to do that again, as inspiration certainly seems to have gone awol once again.

Update:
Having been pondering its whereabouts, I started searching for the book and now have found it!. It wasn't that far away; just not in my consciousness. I quickly found out that this cloud formation is a Cumulonimbus incus (the anvil-shaped top is called an 'incus').