Don't see very many contrails much in Hawaii--most of the trans-Pacific flights go farther North and we're out of the flight paths for Australia flights to the Continental U.S. So, have a question for all you aviation/weather buffs on what I suppose is a pretty elementary question.

So, I faintly remember Contrails in relation to whether there's more moisture in the atmosphere, but can't quite get it down. If the contrails are longer, is there more moisture in the atmosphere or less?

And, how does that affect weather?

This is a border-line TravelBuzz!/OMNI question given the relations of contrails to plane travel, though richard please feel free to move it if deemed necessary.