not my words. The link is doable.
Jorn Olsen works for the Dutton-Lainson Co. in Hastings, Nebraska, and lives by Heartwell Park next to HastingsCollege. The other night, probably just after the big storm hit, he took these photos and sent them to UNL which, then posted them to the following URL. The stadium lights are at the Hastings College stadium just east of his home.
The clouds are called Mammatus clouds and there's a link on this URL that tells about them. They do not precede a tornado, or fortell a storm, but are formed when the air is already saturated with rain droplets and/or ice crystals and begins to sink. The worst of the storm is usually over when these kind of clouds are seen. They are quite rare, and really beautiful.
http://www.hprcc.unl.edu/nebraska/june2004hastings-mammatus.html