Visible and Thermal Images of a Cumulonimbus

A storm cloud approached NearSys Station today. I was curious about it's temperature variations and so took several visible and thermal images to compare. Here are two of the best pairs.

Based on color, the foreground cloud is warmer than the background one.

Bluer regions indicate colder patches of clouds. I think the warmer clouds are those that appear slightly brighter. Slightly darker regions in visible images may be higher altitude portions of the cloud.