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God's Gatling Gun (Part I)

If you ever fly through a fusillade of hail, whether you get to experience an abrupt cacophony of tiny bouncing frozen particles of graupel, or the total panic and pandemonium of genuine hailstones pummeling your airplane, it will get your attention.If you ever fly through a fusillade of hail, whether you get to experience an abrupt cacophony of tiny bouncing frozen particles of graupel, or the total panic and pandemonium of genuine hailstones pummeling your airplane, it will get your attention. Any magical memories of millions of milky little balls unexpectedly bouncing down around you on a summer afternoon will probably be worlds away. Like the bumper sticker says: visualize whirled peas (frozen peas)...
  • Pea sized hail would make loud clicking noises, and after you landed, if you looked really close, you might see thousands of tiny impact marks in the painted surface.
  • If it was marble size, the noise would be deafening, and your airplane would look much worse, even from a few feet away. It would still fly though.
  • But now imagine whirled golf ball size chunks of ice dropped from a 747 flying at 30,000 feet, and reaching 100 knots, then visualize you flying into them at 120 knots. That's a net impact speed of about 155 knots, and an impact angle of about 40 degrees from the horizontal, which corresponds rather well (read: poorly) with your windshield. Translation: If the windshield gave way, you'd have ice in your lap, and your face -- you'd have a mayday on your hands. Your plane would look like a wreck, if you managed to land it.
  • Anything bigger is gorilla hail; it would hit with sledge hammer force and probably cause catastrophic structural damage... and will probably kill you. Although it is true that as individual hailstones increase in size, they're further apart and there are fewer of them, once those suckers get big enough, your airplane can wind up looking like the consolation prize in the Tasmanian Devil Dent Derby.
Everyone complains about the weather, but what can you do about it? As always, our answer is knowledge; arm yourself with knowledge.

IN CASE YOU'RE FROM THE SOUTH PACIFIC...
Hailstones are balls of ice that grow as they're held up by winds, known as updrafts, that blow upwards inside thunderstorms. The faster the updraft, the bigger the stones can grow. Most hailstones are smaller than a dime (in diameter), but hailstones can be as large as baseballs, sometimes even bigger, weighing more than a pound.

    Damage: $1 billion worth to crops and property each year. The costliest hailstorm in the United States was in Denver in July 1990 with damage of $625 million. While crops are the major victims, hail is also a hazard to vehicles--and windows.

    Fatalities: At least on the ground, these are rare in the United States -- the National Weather Service has authenticated only two deaths. The first occurred on May 13, 1939, near Lubbock, Texas. A 39-year-old farmer died of injuries received when he was caught in an open field during a severe hailstorm. More recently, an infant lying in its mother's arms was killed by hail at Fort Collins, Colorado, in 1979. Seemingly authentic reports of hailstorms killing people have come from around the world, notably from China and India, whose populations are very concentrated and where many people live in poorly constructed buildings.

Figure 1 HOW IT WORKS: LOADING THE AMMUNITION
Inside a thunderstorm, during its middle “mature” stage, there is a coexistence of warm updrafts (red) and cold downdrafts (blue), but hail is also associated with the final dissipating stage of thunderstorms, as well. If a water droplet gets lifted above the freezing level, it may freeze. Some water droplets hoisted above the freezing level can also drop below freezing and become supercooled. When they reach an area of downdrafts, the frozen ones may thaw, or get cycled in for another ride upward and grow in size as other super-cooled droplets collide with it and instantly freeze. This explains why hailstones often wind up with a stratified interior resembling an onion -- layers of clear ice laminate with layers on granular ice, known as rime. The layers are formed as the hailstone travels up and down within the thunderstorm. Each time around, it may grow until the updrafts can no longer support it, at which point it may drop toward the ground like a major league fastball.

THE LIFE OF A HAILSTONE
Just as there are three stages in the development of a thunderstorm, there are also three stages in the develoment of hail: graupel, small hail, and hailstones.

  1. Graupel (a.k.a. snow pellets) are opaque ice particles, usually round, though sometimes conical, and have a snow-like structure. Typically their size falls between two to five millimeters in diameter (0.1 to 0.2 inch). They're built from the accretion of previously super-cooled water onto the surface of snow crystals. Once the shape of the original snow crystal is no longer identifiable, it is then referred to as graupel. It's somewhat compressible and since it rebounds from a hard surface, can be mistaken for hail. Note that the weather report contraction of this word -- GR -- represents hail, which is a bit misleading! (Depending on where you look, the term graupel comes from the German word 'graupe', for hulled grain or the French word for hail: 'grêle'.)
  2. Small Hail is the same size as graupel, but has a higher density and a partially glazed surface. Graupel becomes small hail by filling air capillaries within its structure with liquid water. (No, it's not alive.) Small Hail is normally semitransparent, rounded, can consist partly of liquid water, and sometimes has a frozen outer shell. (No, it's not a dessert.)
  3. Hailstones are formed -- officially -- when the junior versions of these icy conglomerations reach a diameter of 1/5 inch (5 mm). They are arranged in layers, can be as small as a pea or as large as a grapefruit, are usually spherical, but can be conical, covered by bumpy outgrowths, or flat.
Figure 2
HAIL HOT SPOTS
Thunderstorms roaring across the country often bring periods of hail to many locations in the Rockies and the Plains during spring and summer. Hail can occur anywhere in the United Sates, but is most common in the Plains states just east of the Rockies, in a region known as 'Hail Alley', which extends southeast from northern Alberta, Canada, into Montana and continues southeast to include the eastern parts of Wyoming, Colorado, and New Mexico, as well as most of South Dakota, Nebraska, Kansas, Oklahoma, and western Texas.

Pilot Homes Guide: North America's most hail-prone city is Cheyenne; it receives an average of 9 to 10 hailstorms per season. Some locations in the higher elevations of the Rockies may experience 20 or more hailstorms annually. Other parts of the world that 'frequently' have damaging hailstorms (besides the US, China, and India) include Russia and northern Italy.

Next week, The Gun, Part II: The Enemy's Secrets, And Taking Cover

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