If you looked at the western sky as the sun set over Southern California Monday you might have seen a spectacular show of contrails.
"When it's humid at higher altitudes contrails remain visible in the sky longer. Spectacular contrails today - like a tic-tac-toe board!" Ian Gregor, Communications Manager, FAA Western-Pacific Region told NBCLA in an e-mail.
Contrails (short for "condensation trails") are artificial clouds that are the visible trails of condensed water vapor made by the exhaust of aircraft engines.