Roll Cloud

This nasty looking roll cloud is taking dead aim on the St. Cloud Middle School in St. Cloud, Florida.  Photographer: Jon Zenzel

Since it seems to be separated from clouds above it, it’s referred to as a “roll cloud.” A shelf cloud is in essence the same as a roll cloud, but it’s connected to an obvious parent cloud.

This cloud is not associated with a tornado. The wind is blowing in the direction that the storm is moving and not towards it, as would be the case with a tornado. However, because roll clouds are sometimes observed to rotate along their horizontal axis, they’re indeed unnerving.

via epod