Just a little bit of randomness here. I was checking the weather today on weatherunderground (http://www.wunderground.com) and I noticed that they list the density of the cloud covering at different altitudes. That's pretty useful and all. Then I noticed what was printed below the cloud cover information. The words "Above ground level" note that it's not above sea level. They're informing us that the clouds are above the ground. As opposed to below it I suppose. I know we call clouds that are AT ground level "fog" but what do you call clouds that are below the ground?