Cloud seeding

Dear Tom,
I used to hear about cloud seeding to create rain, but I don't hear much
about it anymore. What is cloud seeding, and why has it faded away?
Donna Sweetser
Dear Donna,
Cloud seeding is controversial. Thorny legal issues often arise with the
process, and many states have banned it.
Cloud seeding involves adding certain chemicals to clouds, usually to
stimulate cloud development and enhance rainfall production, but there can
be other uses (such as hail suppression) as well.
Cloud seeding does not "create" rain. Rather, it encourages a cloud on the
verge of producing rain to produce more rain than it otherwise might. Many
scientists are skeptical of the results, and meteorologists point out that
clouds favorable for seeding often don't exist when drought conditions
prevail, whereas irrigation systems, though costly, guarantee the desired
benefits.