I live by an airport, and looking up today I noticed a bunch of contrails hanging out when they normally just vaporize.. I understand that there’s probably differences in temperature/air pressure involved but we’ve had some consistent weather the past few weeks and they’ve been hit and miss. what’s happening?
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Contrails form when hot water vapor from an airplane engine mixes with cold air in the sky. Sometimes the air is just the right temperature and humidity for contrails to stay in the sky for a long time. Other times, the air is not as humid and the contrails quickly disappear.
They’re formed by hot jet exhaust condensing in colder air at high altitudes.
Whether they stay put or disperse (or form at all) is a function of the temperature, humidity, and wind speed at that altitude.
You may notice you see a lot more of them in the winter when it’s really cold up there, and practically none in the heat of the summer.
If it’s really windy up there they may disperse quickly even if it’s more stagnant at ground level. Your weather at ground level won’t always reflect air movements higher up.
If the air is cold enough and humid enough for visible condensation of water vapour in the engine exhaust to freeze before it evaporates, then the contrail persists until its ice crystals disperse or sublime back into water vapour. Otherwise, the condensation quickly evapourates and disappears.
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