moments before the downpour

A beautiful evening sky tonight, but only minutes after taking this, the heavens opened with an unexpected, mighty downpour, catching out the unprepared daytrippers.
I wondered whether to blip the colour or mono version of this scene (each shot separately 'in-camera', not converted in Photoshop), but this mono image appealed to me much more. A colour photo can be seen on my flickr page.