Floating on Cloud No. 9?

Did you know the expression 'up on cloud no. 9' to describe a feeling of euphoric exaltation, is based on actual terminology used by the U.S. Weather Bureau?

Clouds are divided into classes and each class is divided into nine types. 'Cloud nine' is the cumulonimbus cloud that you often see building up in the sky in a hot summer afternoon and may peak up to 75,000 feet!  So to say, if one is up on 'cloud nine,' one is feeling exceptionally high. 

To describe how I feel at the moment, I would be sitting on a Stratus cloud like this one here - one with the lowest altitude - dismally gloomy.