If you were to ask people what characteristic Seattle would be known for, I suspect a fair few people would tell you it is rain.  It is true that we have damp winters here but summers (while a little late in starting) are actually rather dry.  However, we can still have some humid conditions which can be good for forming vapor and, if you watch the jets heading in to SEA, you will often see vortices streaming off the flaps and the occasional puffs of moisture above the wings.

Occasionally, the conditions are just right and you get a lot more vapor.  Better still, if this happens in sunny conditions and the planes are slightly backlit, you can get some lovely rainbow effects showing up.  I got lucky with one such day.  Asiana had an A350 coming in at this time so I was treated to some interesting effects.  A Lufthansa 747 and CargoLogic 777F also arrived but I decided to go with video on those to show off the fleeting nature of the vapor is it formed and dissipated.