thundercloud

ukkospilvi a large, dark cloud, usually a cumulonimbus, charged with electricity and producing thunder and lightning; a stormcloud
puhekieltä something menacing and brooding

As the ominous thunderclouds of war gather over the Middle East, countries like France and Russia have threatened to use their veto in the United Nations to thwart immediate U.S. military force against Iraq. - http://www.faluninfo.net/displayAnArticle.asp?ID=7103