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Originally posted by headcheck
I see chemtrails over the Seattle area EVERY DAY. Saw a large one getting sprayed at night for the first time last week, too.
When a contrail first forms it is composed of water and exhaust gasses, below about -40�C the contrail freezes almost immediately (about one second after entering the free atmosphere), then the conditions encountered will dictate the persistence or the disappearance of the contrail.
For the observer on the ground this man-made modification to the upper atmosphere is a very useful weather tool as it can tell the observer about conditions in the upper atmosphere above 30,000ft (300hPa). The basic information is the condition of the moisture loading and the direction and speed of the wind at those levels. If the contrail persists and even enlarges when conditions are positive for the development of ice crystals, occasionally I have seen contrails develop into large cirrus sheets especially when the ice particles are spread out by wind shear.
Well, different flight routes are at different altitudes, and conditions in atmosphere can vary greatly.
Originally posted by Skadi_the_Evil_Elf
For all fellow Seattleites, notice they generally eminated from the south east, near Rainier. From Mc chord Airbase.