Rollin' In

This "mini" storm chase from my home in Cedar Rapids to the Center Point, Iowa exit--a distance of about 11 miles--produced these video frame capture images of a roll cloud approaching from the the northwest as seen northbound on Interstate 380 around 5:37 PM on Friday, June 18, 2010. The top image was located about .2-mile NW of Hagerman Road and about 2 miles south of Toddville, the bottom image was located about .5-mile south of Quail Ridge Road (bridge overpass in the background) and about 3.5 miles south of the Center Point exit (Exit 35). The bright area under the cloud and behind the trees in the bottom image is the flash of lightning. The somewhat rare roll cloud is formed when a thunderstorm's cool outflow races out ahead of the main storm causing warm air to rise only to tumble back down on the backside of the outflow, causing the air to spin horizontally well out ahead of the approaching storm.