A breakthrough experiment has shown it is possible to create heavy snowfall on demand, scientists have said.

The latest cloud-seeding experiment was conducted by a team flying small planes through clouds in Idaho.

Thanks to technological advances allowing researchers to measure snow particles, the technique has been shown for the first time to make snowfall heavier, they said.

"What they've done is identify the chain of events from seeding to precipitation on the ground, which has been sorely needed for the last 80 years," William Cotton, a former professor of atmospheric science at Colorado State University, told the magazine Science.

The act of cloud seeding - sowing tiny particles in clouds to cause them to break into rain or snow - has been studied for decades, but it is only now that researchers say they have proven how it works outside a laboratory.

The evidence for whether the technique works is still contentious however, due to the difficulty of carrying out controlled experiments in the outside world.

One experiment in China in 2009 forced the authorities to close 12 highways around Beijing when snow caused by cloud seeding fell heavily.

In Idaho, the researchers sprayed the clouds with silver iodide from the wings of their aircaft and also using canisters.

They found that within a couple of hours, the snowflakes had grown from a few microns in diameter to eight millimetres - large enough to fall to the ground and settle.

"The radar can only see [water] particles that are big enough, and these clouds had tiny droplets not detectable by radar," said Katya Friedrich, one of the atmospheric scientists behind the research.

"Suddenly, we saw lines appear. It was really astonishing."

Questions remain about whether the technique could work for drought-hit areas, with the technique having been researched since the 1940s in an attempt combat drought.

"Does it make enough snow to make an impact on a water budget?" Friedrich asked in Science. "We still have to answer those fundamental questions."