Thanks, I didn’t know about them before today and this is probably why
en.wikipedia.org/wiki/Hail_cannon
There is no evidence in favor of the effectiveness of these devices. A 2006 review by Jon Wieringa and Iwan Holleman in the journal Meteorologische Zeitschrift summarized a variety of negative and inconclusive scientific measurements, concluding “the use of cannons or explosive rockets is a waste of money and effort”.[7]
There is also reason to doubt the efficacy of hail cannons from a theoretical perspective.[8] For example, thunder is a much more powerful sonic wave, and is usually found in the same storms that generate hail, yet it does not seem to disturb the growth of hailstones. Similarly, hail cannons are placed at ground level, while hail formation occurs at altitudes above 10,000 meters; a device with an effective range of 500 meters, above, would be unlikely to have an impact at an elevation 20 times higher.[9][10][11] Charles Knight, a cloud physicist at the National Center for Atmospheric Research in Boulder, Colorado, said in a July 10, 2008, newspaper article that “I don’t find anyone in the scientific community who would validate hail cannons, but there are believers in all sorts of things. It would be very hard to prove they don’t work, weather being as unpredictable as it is.”