Size and Terminal Velocity
The size of hail stones is best determined by measuring their diameter with a ruler. In the absence of a ruler, hail stone size is often visually estimated by comparing its size to that of known objects, such as coins. Below is a table of commonly used objects for this purpose. Using the objects such as hen's eggs, peas, and marbles for comparing hailstone sizes is often 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 hail stone. 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, use the coding of GS, which is short for the French word grésil.
Terminal velocity of hail, or the speed at which hail is falling when it strikes the ground, varies by the diameter of the hail stones. A hail stone of 1 centimetre (0.39 in) in diameter falls at a rate of 9 metres per second (20 mph), while stones the size of 8 centimetres (3.1 in) in diameter fall at a rate of 48 metres per second (110 mph). Hail stone velocity is dependent on the size of the stone, friction with air it is falling through, the motion of wind it is falling through, collisions with raindrops or other hail stones, and melting as the stones fall through a warmer atmosphere.
| United States | Canada | |
|---|---|---|
| Dime | 0.705 inches (17.9 mm) | 18.03 millimetres (0.710 in) |
| Cent (or "Penny") | 0.75 inches (19 mm) | 19.05 millimetres (0.750 in) |
| Five cents (Nickel) | 0.88 inches (22 mm) | 21.2 millimetres (0.83 in) |
| Twenty-five cents (Quarter dollar) | 1.00 inch (25 mm) | 23.88 millimetres (0.940 in) |
| Dollar (Loonie) | 1.043 inches (26.5 mm) | 26.5 millimetres (1.04 in) |
| 50 Cents/Half Dollar | 1.25 inches (32 mm) | 27.13 millimetres (1.068 in) |
| Two Dollars (Toonie) | 28 millimetres (1.1 in) |
| Object | Diameter |
|---|---|
| Pea | 0.25 inches (6.4 mm) |
| Marble (small) | 0.50 inches (13 mm) |
| Mothball | 0.50 inches (13 mm) |
| Grape (small) | 0.62 inches (16 mm) |
| Olive (large) | 0.75 inches (19 mm) |
| Shooter Marble | 0.75 inches (19 mm) |
| Walnut/Ping-pong ball | 1.50 inches (38 mm) |
| Ping-pong ball | 1.60 inches (41 mm) |
| Squash ball | 1.65 inches (42 mm) |
| Golf ball | 1.75 inches (44 mm) |
| Hen egg | 2.00 inches (51 mm) |
| Billiards (Pool) Ball | 2.25 inches (57 mm) |
| Orange (Valencia/sweet) | 2.38 inches (60 mm) |
| Tennis ball | 2.50 inches (64 mm) |
| Baseball | 2.75 inches (70 mm) |
| Cricket ball | 2.80 inches (71 mm) |
| Teacup | 3.00 inches (76 mm) |
| Grapefruit | 4.00 inches (102 mm) |
| Softball | 4.50 inches (114 mm) |
| Melon (small) | 4.75 inches (121 mm) |
| Computer CD | 5.00 inches (127 mm) |
| Cantaloupe | 6.50 inches (165 mm) |
| 45 RPM Phonograph Record | 7.00 inches (178 mm) |
| Volleyball | 8.00 inches (203 mm) |
| Bowling Ball | 8.25 inches (210 mm) |
Read more about this topic: Hail
Famous quotes containing the words size and/or terminal:
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—Aristotle (384 B.C.–322 B.C.)
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—W.H. (Wystan Hugh)