Mammatus Moment

Resembling lava lamp globules, these very pronounced mammatus clouds filled the sky over the western horizon at Bowman Woods Park in Cedar Rapids, Iowa on Friday evening, July 24, 2009. The clouds appeared about an hour before a strong storm moved through the area and captured the gaze of many curious backyard sky observers. Mammatus clouds often form in a very moist and unstable middle or upper level in the atmosphere, overlying a drier layer below an adjacent cumulonimbus anvil. Large mammatus formations can be indicators of imminent severe weather.