These photos were taken by Jorn Olsen.
He works for the Dutton-Lainson.Co in Hastings, Nebraska, and lives by Heartwell Park next to Hastings College. The other night he took these photos, the stadium lights are at the Hastings College stadium just east of his home.The clouds are called Mammatus Clouds. They do not precede a tornado, or foretell 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 kinds of clouds are seen.
They are quite rare, but really beautiful.