I'm not sure if it's a result of being from a particularly cold/rainy part of the world, but I love cool, misty days. Not rainy days, mind - if I'm in the field, rain makes note-taking annoying, to say the least, and I hate getting soaked and standing around in wet clothing.
But I love a foggy day, with the temperature somewhere between cold and hot (or 45 - 60) - the feeling of moisture condensing on my face. Warm, sunny days are nice too, but they don't evoke the same feeling of home.
Today was misty and cool all day, but not a drop of actual rain. I didn't get as much work accomplished as I'd hoped, and we ran into the sort of annoying problems that always seem to plague fieldwork (stuff forgotten, subcontractors somewhat obstinant in doing something I didn't especially like), but it was still a day that made me happy.