Scene Again

I just looked up vapour trails and it says in Encyclopaedia Britannica "also called Condensation Trail, or Contrail, streamer of cloud sometimes observed behind an airplane flying in clear, cold, humid air. It forms upon condensation of the water vapour produced by the combustion of fuel in the airplane engines. When the ambient relative humidity is high, the resulting ice-crystal plume may last for several hours. The trail may be distorted by the winds, and sometimes it spreads outwards…" so there we have it - we obviously have clear cold humid air here!
You learn something every day, don't you? *bg*