Prime conditions for cloud seeding generally occur during the winter when cumulus clouds and the moisture content within the clouds are high.
SACRAMENTO – A. Vassallo asked the following question, posted to the News10 email address:
"Why while we have had this monsoonal cloud cover, for several days now, has no one sent up cloud seeding airplanes. Just think of all the moisture we have let slip on by?"
Cloud seeding is a weather modification to artificially stimulate the amount or kind of rain or snow. The most common chemical used for cloud seeding is silver iodide. Dry ice and potassium iodide can also be used.
The chemical is put into the clouds either by ground generators or by airplanes. Once the chemical is in the cloud, water droplets form on the silver iodide particle, just as it would naturally occur on dust or pollen.
The conditions have to be prime for cloud seeding. The type of clouds over the region from the monsoon moisture are mainly stratus clouds. These are low-level clouds that are layered in the atmosphere. They are formed of ice crystals.
Cloud seeding works best with cumulus clouds, the white billowing clouds that tower high into the atmosphere. The cumulus clouds hold more moisture and the cloud tops range between 6,000 and 23,000 feet into the air. The winter season produces conditions most conducive for cloud seeding.
According to the California Department of Water Resources, winter orographic cloud seeding has been practiced in the state since the early 1950s.