It is very satisfying to notice the first long contrail, it’s one of the earliest warnings of a weather change. A front is likely on its way.
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”). The white lines only last if there is enough moisture in the atmosphere at that level.
If you notice that a clear blue sky has changed and suddenly appears to be covered in lots of long white contrails, it’s a sign of moisture high in the troposphere and means wet weather may be on the way. But spotting the first long contrail is very satisfying.
For more see the book, The Secret World of Weather.
24 hours after seeing the contrail above, the sky looked like this:
You might also enjoy:
How to Forecast the Weather with Contrails
How to Navigate Using the Upper Winds and Clouds