In nature you some times see small vertical features like this most often small clouds under the right conditions, under these conditions there is often high wind levels and clouds tend to race across the sky quite quickly, under these conditions it can be expected that there will be heavy rain; the sky in this image reflects the almost green sky you'd expect under such conditions and the lighting is about what you'd expect also.
These smaller clouds due to there size move faster across the sky then the larger clouds (Which are moving quickly but much slower relatively specking) due to there size, there position lower in the cloud base and higher relative wind speed at there given altitude.
Regards to you.
Cyber-Angel
