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Posted by on Jun 1, 2016 in Tell Me Why |

What Makes Hail?

What Makes Hail?

During a thunderstorm, balls of ice, called hail, may fall. Hail starts as rain. Before the drops can fall, strong air currents carry them to the upper part of the cloud, where it is freezing cold.

The drops turn to ice and get a coating of snow. As they start to fall, the drops pick up a coat of rain, and again the wind forces them upward.

Up they go time after time, adding more coats of ice and snow, until at last the air currents let them fall to earth. Hailstones are usually not much bigger than peas, but sometimes they can be as large as tennis balls.

The size of hailstones is best determined by measuring their diameter with a ruler. In the absence of a ruler, hailstone size is often visually estimated by comparing its size to that of known objects, such as coins.

Using the objects such as hen’s eggs, peas, and marbles for comparing hailstone sizes is imprecise, due to their varied dimensions.

The UK organisation, TORRO, also scales for both hailstones and hailstorms. When observed at an airport, METAR code is used within a surface weather observation which relates to the size of the hailstone.

Within METAR code, GR is used to indicate larger hail, of a diameter of at least 0.25 inches (6.4 mm). GR is derived from the French word grêle. Smaller-sized hail, as well as snow pellets, uses the coding of GS, which is short for the French word grésil.

Content for this question contributed by Chris Valiquette, resident of Walnut, Los Angeles County, California, USA