Jim Brandenburg / Prairie under threatening thunder clouds, South Dakota

Gerry Ellis / Altocumulus thunder head dumping rain on pan, Amboseli National Park, Kenya

Tim Laman / A giant thunderhead cloud building up over the Sungai Petani mangrove forest. Sungai Petani vicinity, Kedah, Malaysia. May 2006

Yva Momatiuk & John Eastcott / Sagebrush prairie and heavy cumulus clouds, Nevada