VIDEO: Massive shelf cloud rolls into Galveston

GALVESTON, TX (KTRK) -- An ominous looking "shelf cloud" blew into Galveston this morning, and we captured this video of it on our TowerCam!

Watch the video above.

Also known as an "arcus cloud," this wall of moisture formed along a dying cold front, stretching in both directions as far as the eye could see.

It rolled into Galveston around 8am, and while most shelf clouds are followed by intense rain, this one produced no precipitation at all.

This unusual cloud forms when warm, moist air rises over a wedge of colder air moving in the opposite direction.

Another type of arcus cloud is called a "roll cloud." It forms under conditions similar to a shelf cloud, but it is completely detached from any other clouds. One of these rare roll clouds was spotted over north Houston this past weekend.