https://bcwwa.org/resourcelibrary/Fall%202012%20-%20Weather%20Modification%20and%20Geoengineering.pdf

Persistent Contrails:

Many people have begun to notice what NASA has termed “persistent contrails.”
For those who have not observed the phenomena, spend some time watching the sky
throughout the day, and if weather conditions are right, you will see contrails
linger in the sky all day and eventually spread out. If you are in a high air
traffic path, you will notice that the sky will eventually be covered in a
contrail haze. The potential impact of this on climate has become such a concern
that NASA has developed an online tool for predicting where and when persistent
contrails will form so that air traffic can be re-routed.

You can view this resource at:
http://enso.larc.nasa.gov/sass/contrail_forecast/contrail_prediction.html#REALTIME.
With air traffic expected to increase, and environmental conditions possibly
changing to favor the development of persistent contrails, we may find that
clear blue skies will not be so common in the future.

Most people now accept that day-to-day human activity is inadvertently modifying
global climate. Less well known, however, is that active weather modification
has also been around for a long time, and is becoming increasingly prevalent
today. Active weather modification may have begun with the observation that it
often rained after field battles, which was attributed to the smoke from cannon
and gunfire. This observation spawned a generation of rainmakers, one of the
most famous of whom was Charles Hatfield.

Hatfield, the American Rainmaker, was purported to have developed a secret brew
of 23 chemicals intended to make it rain, which he released from towers that he
constructed. He claimed to have over 500 successes, and was paid for his
rainmaking abilities. One of Hatfield’s more notable results occurred in San
Diego in late 1915 when he was hired by City Council to fill the Morena Dam
reservoir. Hatfield wanted to get paid $1,000 per inch up to 50 inches, and any
rain after that was free. Council voted in favor of a $10,000 fee payable when
the reservoir was filled. Hatfield immediately got to work on building a six
meter tower, which was in operation at the beginning of January 1916. Heavy rain
began on January 5 and continued throughout the month causing massive damage,
which included a dam failure that resulted in a number of people losing their
lives.

To read more about the Rainmaker, visit:
http://www.sandiegohistory.org/journal/70winter/hatfield.htm