More hail cannons, but not much more evidence.

The lesson for today is “Just because I can't disprove it doesn't mean you have sound evidence.”

According to USA Today, more farmers are investing significant capital in cannons to guard against hail damage. How are they supposed to work? When Doppler signals a nearby storm, the cannons let out loud electronic blasts every few seconds. The manufacturers claim that sound waves from the cannon disrupt airborne water droplets, preventing them from developing into hail stones.

Scientists dispute these claims. I can see why farmers are willing to try new ways of protecting crops -- I just hate to see them spend hard-earned money without supporting evidence. Evidence Soup wrote about hail cannons last year:

There is anecdotal evidence that this works: 'For the last few years, the fields that got hailed on were the fields that were unprotected,' said Amy Kunugi, general manager for Southern Colorado Farms. But scientists dismiss the effectiveness of this approach, saying that... 'thunder - louder than the cannons - would occur in the same storm, and would disrupt creation of hailstones more effectively than a sonic wave.'

In a July 10, 2006 story, the Rocky Mountain News quoted Charles Knight, a cloud physicist at the National Center for Atmospheric Research in Boulder: Though he said he was unaware of any NCAR scientists who had validated the effectiveness of hail cannons, he acknowledged that "It would be very hard to prove they don't work, weather being as unpredictable as it is."