Can "hail cannons" really protect a vineyard?
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Dear Dr. Vinny,
With all of the hailstorms that have been plaguing Europe, I have read a mention here and there about “hail cannons.” I gather these are designed to prevent/minimize the damage, but have no idea how they work or if they are in any way effective. Can you help me out?
These stories about hail have been bumming me out. There are two different types of “cannons” shot at hail, one of which seems to work well enough, while the other is less conclusive.
One hail cannon is a cone-shaped tower that’s supposed to disrupt the formation of hailstones by creating shockwaves. An explosive charge of acetylene gas and air is fired through this tower, which makes a loud boom followed by the annoying reverberating whistling sound of a 200 mph shockwave. The thinking is that the shockwave will disrupt the hailstones as they’re forming.
I’ve seen some video footage of these hail cannons and, man, they are really loud, and not only that, they’re fired repeatedly every minute or so as a storm is passing. As you might imagine, if you live next door to someone using a hail cannon, you’re going to hate it, because it sounds like artillery fire. Some farmers feel that the price tag ($50,000 and up) is a better investment than hail insurance.
The effectiveness of these hail cannons is pretty inconclusive. Some people swear by them, while others point out that thunder also creates loud booms and shockwaves, but it often hails in the middle of a thunderstorm. Hail cannons may have developed out of the firing of actual cannons that were set off as storms approached, which evolved from the practice of ringing church bells at the sign of a storm. People making loud noises during storms seems to have a long history.
Then there’s another type of cannon that shoots silver iodide into the air, a process known as ground-based “cloud seeding” (cloud seeding can also be performed from an airplane). Silver iodide lowers the temperature in clouds and creates ice crystals, which can then fall in the softer forms of snow or slush rather than hail.
Cloud seeding seems to be effective but unpredictable. It might vary because of other variables at play, such as temperature and cloud composition. Some folks are nervous about the supposedly non-toxic silver iodide, and moreover, it’s expensive.
One problem with both of these devices is that it’s difficult to do experiments on their effectiveness, as you would have to watch hail not being formed. Also? We can’t really control the weather.