The very earth herself tells you a storm is coming. Here's a good one to try when you want to impress your friends. Walk outside some day, look up into a clear blue sky, and tell them in will rain within 24 hours. After they are through laughing, just smile and show up the next day in a raincoat and laugh as they get wet. Just don't tell them you used jet contrails to make your prediction.
Contrails are a trail of condensed water vapor produced by jet aircraft flying at high altitudes.
The water droplets freeze within seconds and ice crystals develop. Even small particles released in the exhaust fumes are sufficient to generate ice crystals and hence condensation trails. When jets produce very short trails that dissipate quickly there is very little moisture in the atmosphere at jet level, indicating dry weather for a while. But when long trials hang around and begin to criss-cross the sky, there is an abundance of moisture at high levels. Clouds could begin to form within hours and look for rain within 24 hours.