The USGS Water Science School
The Little Cloud That Could ... But Why?
Late October in Atlanta, Georgia is the peak of autumn, often with cool, crisp days, clear blue skies, and trees full of fall colors. A perfect time of year to, well, take off of work early and go home and lay in the hammock. Which is just what I was doing one October day when I looked up and noticed this tiny white cloud floating all by itself in an otherwise totally blue sky.
If you read our page about condensation and the water cycle, you will have a better understanding of why clouds form. Clouds form in the atmosphere because air containing water vapor rises and cools. Of course, water is involved, but also temperatures and change in temperature with a gain in altitude. Water vapor in the air condenses into cloud particles under certain conditions, forming visible clouds.
For this little cloud to form, certain meteorlogical conditions must be present, but what was so unique about that area of maybe a few hundred square meters that would allow this lonely cloud to form? What puzzled me so much was trying to figure out how the weather conditions would be right for cloud formation in the one very tiny section of the sky, but not a few hundreds yards above, below or next to it? Out of the whole expanse of many square miles of the sky, what was happening in this tiny dot of the sky that would allow a cloud do form, and form just right there?
The answer is—I don't know! Likely a difference in humidity or the concentration of vapor or maybe a spot of warmer or colder air? So, I can't provide an answer, but if any of you are weather experts have the knowledge, please email me with a scientific answer and I will post it here.