On days with little wind at the surface, there will likely be calmer winds in the middle and upper levels of the atmosphere. Calm winds aloft allow the visible white
streams from aircraft exhaust, or contrails, to be seen for a longer period of time. When there are stronger winds the atmosphere mixes and contrails dissipate sooner.
However, calm winds on day one does not mean it will be windy the next. Winds are generated by difference in air pressure. A weather pattern that produces calm winds can last for days, and until a low pressure system approached and squeezes near an area of high pressure, calm winds continue.
Contrails have been described as man made clouds. When the water vapor condenses and freezes from the tiny particles in jet engine exhaust, it becomes visible. Some of the water vapor comes from the air around the plane, and formation depend a lot of the temperature and moisture of the atmosphere.
I receive questions about contrails because of the interesting pattern they make in the sky. I was sent a picture a few years ago, where the photographer thought
there was a high altitude game of tic-tac-toe going on.
From time to time I am asked about chemtrails. Though they often look similar to contrails some very strongly believe they are trails of chemicals the government puts into the atmosphere. These folks are very passionate and enjoy debating.
Next time you have some time search “chemtrails” on the Internet. It’s interesting stuff, but I am still not a believer, at least not yet.
If you have a weather question for Dan, send it to: askdan@kjrh.com
