Cloud streets are shown forming over the Sea of Japan in this image captured by the MODIS on the Terra satellite. The Sea of Japan is nestled between western Japan and Eastern Russia. North and South Korea make up the southwest border of the sea. This image was captured on December 31, 2009.
The lines of clouds are called "cloud streets." Cloud streets have been observed frequently, both by airplane and satellite. These clouds are really cumulous clouds, which result from thermals, or rising columns of warmed air. Thermals themselves form when the ground surface is a little warmer than its surroundings. If the thermal produces a consistent flow of warm air, and steady wind carries that air away, lines of clouds can form along the direction of the wind. An irregular surface may provide the perfect conditions for creating steady streams of warm air interspersed with areas of cooler air.
At the point where the clouds first form streets, they're very narrow and well-defined. But as they age, they lose their definition, and begin to spread out and rejoin each other into a larger cloud mass.