CHEYENNE, Wyo. (AP) — Preparations are being made for a final winter of seeding clouds over Wyoming mountains as part of the state's unique research project to determine whether the practice actually works.

The state has invested about $13 million since 2005 in the project, which seeks to determine whether cloud seeding increases the amount of snowpack in several of the state's mountain ranges.

Cloud seeding involves injecting silver iodide into clouds. Under the right conditions, the chemical can help water droplets grow and fall to the ground.

The Wyoming project has been hampered by drought conditions that have limited chances for cloud seeding the past two winters.

Project manager Barry Lawrence, of the Wyoming Water Development Office, says he's cautiously optimistic that enough cloud seeding cases will be obtained for a valid study.