Here in the Rural High Country, you see these things about once a week over the mountains just west of where I live... It happens early in the mornings at extreme altitude and fans slowly into a dirty high altitude haze... if it was water it would evaporate and be gone quickly... or you may think it's a toilet dump... that's one huge toilet storage tank. These are fire tankers dumping fly ash at close to 40,000 ft.~JT