Below is a short excerpt from the book, The Secret World of Weather, on how contrails can be used to predict changes in weather
Contrails
Watch high jets pass over you and you will notice how sometimes they leave long, straight, white lines behind them and sometimes they don’t. The long white lines are jet-made clouds known as contrails.
Contrail is short for “condensation trail,” and the clue they offer us lies in the name. The aircraft are flying at a height where these clouds can always form, so the fact that sometimes they do and sometimes they don’t reveals something about the moisture levels and wind in the atmosphere at that level.
The best way to think about contrails is not actually to ask whether they form, but how long they last. It is best to assume that contrails are forming behind every aircraft, then either disappearing instantly or lasting for long periods.
The contrails that last a long time indicate moist air and the ones that disappear instantly signify dry. A trend from a blue sky with no contrails toward lots of these white lines stretching over your head is a clear sign of rising moisture levels in the atmosphere. And this is one of the signs of an approaching warm front and rain.
Continued in the book, The Secret World of Weather, by Tristan Gooley.
24 hours after seeing the contrail above, this is what the skies looked like:
