Now that we’re starting to see some precipitation in the Upper Basin, cloud seeding programs can help us generate more snow and potentially reduce some of the impact of the initial dry winter months.

Snow Covered MountainThis is one part of how Central Arizona Project, as a water manager, looks for every opportunity to develop water supplies through conservation, augmentation and maximizing existing supplies.

Here are a few frequently asked questions and answers about weather modification – otherwise known as cloud seeding. 

Q: How does weather modification work?

At CAP, when we’re talking about weather modification, we’re usually referring to augmenting the winter snowpack. This involves seeding clouds with material that acts as a catalyst to start, increase or accelerate ice nuclei production. The introduction of additional ice nuclei into a cloud promotes a cloud to produce more snow at temperatures that may be slightly warmer than is typical. We expect to see more precipitation over a target area.

Q: What conditions are needed for weather modification to work?

For a cloud to be seeded effectively, several conditions need to occur. The clouds that will be targeted for seeding must persist long enough for adequate cloud seeding to take place. Additionally, the forecasted trajectory of the storm must coincide with the generator locations and the target seeding site. And, ideally, the temperature will be between 0 and -5 degrees Celsius.

Q: How effective is weather modification in enhancing winter precipitation?

The most recent and relevant analysis by the Wyoming Water Development Office from its six-year randomized cloud seeding study indicated a 5 to 15 percent increase in winter precipitation.

There is a common misconception that cloud seeding reduces the natural precipitation downwind of a target seeding area. However, this concept assumes that a cloud has access to a finite amount of water vapor. In reality, the atmosphere is saturated with water vapor and clouds continually absorb more water vapor to produce precipitation. The net outcome is that precipitation is typically increased, not decreased, downwind of where cloud seeding is taking place.

Q: Can weather modification work too well – produce too much snow that might create adverse weather events?

The winter cloud seeding programs that CAP participates in have safety measures in place to avoid exceeding snowpack thresholds that may lead to events such as avalanches or flooding during the snow-melt season.

Q: Where is weather modification taking place?

Weather modification has been used in more than 20 countries since the 1950s. In the Colorado River Basin, winter cloud seeding programs are currently active in Colorado, Wyoming and Utah.

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