Are you positive it was white? Does it continue as you drive? You mention your fluid levels are good and it doesn't do it everytime.. I agree with smiley3033. It seems a little odd to me that you would be having head gasket issues.. Not that its impossible, I just find it unlikely..
The smoke, is it maybe sorta blue at all..? I only ask because like already stated white smoke is a symptom of head issues, but your issue could be as simple as the PCV valve going bad... Once they get warmed up the can stop smoking till the next cold start up.. plus smoke color can be decieving sometimes, as dumb as that sounds.. Just throwing the idea out there..
Keep checking your radiator to make sure the level doesn't drop.. I certainly hope its not a cracked head issue..