How to find out if they are spraying above your head. There are parameters for a contrail to form.
The temp must be colder than -38C. The Humidity level must be above 55%
The warmer it is, the more humidity needed to form a contrail.
below 55%, contrails will not form, according to NASA.
above -38C, contrails will not form.
Atmospheric Soundings.
Satellite Meteorology. Methods for retrieval of atmospheric temperature and humidity profiles.
http://weather.uwyo.edu/upperair/sounding.html
Predicting Contrails Using an Appleman Chart [Student]
Background: Military planners have been interested in condensation trail (contrail) forecasts since World War II. Contrails can make any aircraft easy to locate by enemy forces, and no amount of modern stealth technology can hide an aircraft if it leaves a persistent contrail in its wake. In 1953, a scientist named H. Appleman published a chart that can be used to determine when a jet airplane would or would not produce a contrail. For many years, the US Air Force Global Weather Center used a similar chart to make contrail forecasts.
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