in fact any thunderstorm has such ice balls.
the warm air goes up through thermal reasons, cools out and freezes.
the frozen water forms balls around ~10 cm.
these fall down, smashing on upstreaming ice balls.
without that crashes there couldnt be a flash or thinderstorm at all.
they dont reach the ground normally cause such is happening always in warm atmosphere.
in southern germany theres such happenings very often (if u believe the insurances).
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