Towering thunderstorms erupt over the American prairies to delight from afar and terror underneath. These violent clashes of airmasses can produce rotational winds that occasionally culminate in a tornado touching down. More often, however, the rising air currents are responsible for sending droplets of moisture through a roller-coaster path from the bottom to the top of the cloud. If the updraft is strong enough to repeat this with increasingly-larger iceballs that form with each cycle, the hailstones which eventually break this grasp and fall to the Earth’s surface become accordingly larger.
A larger hailstone is less buoyed by air turbulence and, so, it falls faster as its diameter increases. Couple this with the added mass, and increases in hailstone size begin to exponentially increase the resulting strike force. A 1-cm growth in hailstone diameter, for instance, can mean the difference between a stinging pelt, a stunning impact, or even a deadly blow (depending on the species in question).
In the attached graph, the more than century old data produced by Martin (1907) are plotted. The lines indicate how hailstone speed (right y-axis) and strike force (left y-axis) increase as a function of hailstone diameter. Also shown are the animal body sizes – by weight – that Martin (1907) estimated would be stunned by the corresponding hail strike.
Martin, Paul. 1907. “Étude Sur La Grosseur Des Grelons Dangereux Pour Les Oiseaux.” In Proceedings of the Fourth International Ornithological Congress, edited by Ernst J.O. Hartert and J. Lewis Bonhote, 656–58. London: Dulau & Co.