Cloud streets are parallel rows of cumulus clouds that line up in the direction of a steady wind.
The lines are typically about five miles apart, with clear sky between, and they can extend for hundreds of miles.
Also called "horizontal convective rolls," they often form over flat country in spring or summer when the wind is blowing beneath an inversion layer. As the wind travels under that layer, it divides into a series of counterrotating cells. Where the air in two adjacent cells lifts upward, a line of clouds forms, and where they join to spin downward, clear air prevails.
Glider pilots can stay aloft for miles by following cloud streets.
Wikipedia on Horizontal Convective Rolls
Photo by Stu Ostro from Weather.com