Jorn Olsen, who lives in Hastings, Nebraska, took photos of rare mammatus clouds over the city on December 6th, 2004. Three of his photos were featured on the front and back cover of the Journal of Meteorology and distributed internationally. The photos depict mammatus clouds, which are pouch-like structures seen hanging below thunderstorms and do not necessarily indicate an imminent tornado.

29. These photos were taken by Jorn Olsen, he lives on Heartwell Park in Hastings, Nebraska. Spectacular Mammatus Clouds over Hastings, Nebraska December, 6th, 2004 Three of these extremely rare photos were featured on the front and back cover of the Journal of Meteorology and circulated in 26 countries. UNL University of Nebraska-Lincoln High Plains Regional Climate Center

30. UNL University of Nebraska-Lincoln High Plains Regional Climate Center Mammatus Clouds Mammatus are pouch-like cloud structures and a rare example of clouds in sinking air. Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean that a tornado is about to form; a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed. Mammatus typically develop on the underside of a thunderstorm's anvil and can be a remarkable sight, especially when sunlight is reflected off of them.