Roll Cloud

Saw this Roll Cloud out of my office window this morning.  Roll clouds can be caused by downdrafts associated with thunder storms (and you can see rain on the left side of the picture).  The forecast is calling for lots of rain later this afternoon & evening, and all day tomorrow.  Some parts of the area could see up to four inches of the wet stuff!

From Wikipedia: A Roll Cloud is a low, horizontal, tube-shaped, and relatively rare type of arcus cloud. They differ from shelf clouds by being completely detached from other cloud features. Roll clouds usually appear to be "rolling" about a horizontal axis. They are a solitary wave called a soliton, which is a wave that has a single crest and moves without changing speed or shape.