Cloud Seeding

Cloud seeding is a type of weather
modification that aims to change the amount
or type of precipitation that falls from clouds by
dispersing substances (such as silver iodide,
potassium iodide and dry ice (solid carbon
dioxide) and liquid propane) into the air that
serve as cloud condensation or ice nuclei.

• Benefit: It improves a cloud’s ability to
  produce rain or snow, supplements the
  rainwater supply and cleans the
  atmosphere by introducing tiny ice nuclei
  into certain types of subfreezing clouds.
• These nuclei provide a base for snowflakes to form.