To go back to the air mass talk from the previous page I thought that this might be of interest:
A larger image is here:
http://farm8.staticflickr.com/7102/7...7d5ef47e_o.png
It's a satellite-derived map of air mass that we produce, this image is from yesterday afternoon. The air mass types are the same as BotB mentioned and also included is an indicator of whether the air is stable or unstable. Because it's from satellite data the image isn't a direct measurement of air mass type - we can't get that information directly - but instead it uses some clever tests on the data we do have in order to derive an indirect 'guess' or the air mass type. In most conditions it does a pretty good job but occasionally it gets confused - a few times I've seen it conclude that air over the Sahara is polar, for instance.