When we went out to look at the sunset this evening, Verna took this photo of these rippling altocumulus clouds to the southeast of our house. This is an unusual cloud formation that generally occurs in advance of an approaching storm front. Sure enough, the National Weather Service is forecasting a 40 percent chance of rain tonight.
The clouds are formed when a wave is generated aloft; that is, the air mass is rising and falling in a wave-like motion as it is carried along in the upper atmosphere. The water vapor in the air condenses into droplets or ice crystals when it rises and evaporates again when it comes down below into warmer air.
Regardless of all the nerdy science involved in explaining the phenomenon, it sure is pretty to see up there. Click on the image to enlarge.