If you want current information on flights in our skies or any place in the world check out https://www.flightradar24.com. The site provides a live map showing  ground speed, calibrated altitudes, type of aircraft, stating point, destination etc. of all commercial fights. I am not sure if it is amazing or scary (from an environmental perspective)  at how many flights take place daily over the Alaska skies and the world. But I find it interesting that two flights on nearly the same fight path, at nearly the same altitude and speed can produce two different jet exhaust streams. Take Tuesday afternoon as an example. I counted nine distinct contrails in an east/west pattern over a 2-3 hour period. These jet trails lingered in the sky for hours drifting north with the upper airstreams.  Data from flightradar24 confirmed that 13 fights flew the same flight path, same elevations and speeds during that time frame but only 9 flights left contrails from horizon to horizon. How does that work?