Sometimes, looking at a cloudy sky from below, it is difficult to appreciate that different weather systems develop at various altitudes. The shadow along the margin between these two cloud systems shows that the system on the left is at a higher altitude than that on the right. The two cloud systems are traveling in different directions — upper level winds blow in a different direction from those closer to the Earth's surface in most regions.
STS 41-G, October 1984. Picture #17-31-099.