16 August 2011
A viewer (Eric Atkins) sent me this pic a few weeks back, and it has stumped quite a few meteorologists including me! At first it looks like the cloud in the foreground is casting a shadow on the cirrocumulus deck above and behind it, but this cannot be so! The sun is behind the cloud and not opposite the view from the camera. I have some fellow meteorologists looking into it around the country, but it may very well be a shade being cast on a haze layer above.
Meteorologist Roger Edwards at the Storm Prediction Center in Norman is an avid weather photographer and he has a very similar image here. I’m emailing him and will let you know what he thinks.
Update 16 Aug. : from Roger Edwards:
You’re right on track. I took a similar photo back in 1996, from a similar sun-relative angle: