Unless you were in a windowless room, it was nearly impossible to miss the low, ominous, gray cloud gliding slowly over Bozeman Monday morning. Known as a shelf cloud, the formation is not unusual, National Weather Service meteorologist Nick Langlieb said. However, it is unusual for a shelf cloud to float so low to the ground. “It looked more ominous because it wasn't a couple thousand feet in the air,” he added. Shelf clouds form when relatively cool air associated with a line of showers meets warmer air, causing condensation and creating a cloud. Read and See More Pictures at The Bozeman Daily Chronicle: Environment.