10. Lenticular Clouds
There are any number of reasons why the vast majority of UFO sightings are spurious. Most occur in the United States, most are at night, and the few sightings made in the daytime generally involve lenticular clouds. It's true these remarkably smooth formations don't resemble clouds so much as giant lenses or saucers, but they look like spacecraft even less. Altocumulus lenticularis, their formal name, are most often seen on the downwind side of mountains or mountain ranges (although they can occasionally be found elsewhere), when stable, moist air is present. The clouds are also notable for remaining in place for long periods of time, sometimes to the point of stacking up, one atop the other. Airline pilots generally avoid lenticular clouds because of the turbulence they can generate, although they're a favorite of gliders for their generous vertical lift.
9. Thunder Snow
It's just a thunderstorm that develops during the wintertime, right? Well, not exactly. While it is true that some thunder snow events simply begin as regular thunderstorms and then get colder, a precise, narrow set of circumstances has to be present for thunder snow to occur. In thunderstorms, instability is created when warm, moist air at the surface rises into colder air aloft. But for thunder snow to transpire, the air at the surface still has to be cold enough for it to snow, and that's a very small window. If you hear thunder snow, chances are you're experiencing an exceptionally strong snow squall. It's also believed that most thunder snow events happen in early or late winter, not in the middle of the season, but this isn't strictly always the case. As for snow lightning, don't expect to notice much more than a general brightening of the sky.
8. Ball Lightning
Plausible explanations exist for every phenomenon on this list, except ball lightning. There have been countless sightings of it through the centuries, including a great many close encounters, but the seemingly endless ways in which ball lightning can behave, together with the fact that it hasn't been successfully replicated in the laboratory, have given rise to a plethora of highly technical reasons for its existence. One thing is obvious — it is associated with thunderstorms. Ball lightning is often the size of a tennis ball, although it can be smaller or much larger. It moves crazily, seemingly without logic, since it travels along whatever best conducts electricity. It isn't often deadly, although it can be. Four people were killed and 60 injured when ball lightning nearly destroyed a church in Devon, England in 1638. Some parishioners were playing cards in the pews, and God's wrath was blamed.
They're among the more graceful and delicate of the weather phenomena listed here, not showy or violent, which is perhaps why they're so often overlooked. These so-called false suns, which can be found shining on both sides of the real sun, are typically visible when the sun is close to the horizon, in colder climes and at colder times of the year, although they can appear under other conditions. Crystals — hexagonal ice crystals, specifically — and their amazing properties are behind it all. Light from the sun passes through them, causing the crystals to act as prisms and deflect the light toward us at an angle of 22 degrees. If the sundogs aren't too bright, you can look closely and see a spectrum of rainbow light, from red on the side facing the sun to blue. If the sky is chewed up with clouds, a single patch of rainbow light can often be seen on either side of the sun, which is known as iridescence.
6. Mammatus Clouds
They have the distinction of being the most Photo-shopped of all cloud formations, which seems unnecessary given how distinctive they appear without being artificially enhanced. Their bark is worse than their bite, however. The low-hanging, pendulous clouds, so named because they resemble a woman's breast, appear in lobe-like groupings, and are always associated with severe weather. They have a tendency to develop under the anvil of a cumulonimbus cloud, but it is subsiding air that causes their formation. For this reason, the appearance of mammatus clouds generally means the strongest part of a thunderstorm is past. This is also why mammatus are often seen with the sun shining on their weighty undersides. They make for a stunning sight, but are best photographed from the ground. Pilots are wise to avoid them.
5. St. Elmo's Fire
It's often confused with ball lightning, although it shouldn't be. For one thing, St. Elmo's fire is better understood. Like fire, it's a mixture of gas and plasma. Like ball lightning, it usually occurs during a thunderstorm. Air around an object that's typically pointed and high, although it can be at ground level, becomes ionized by an electrical field and a faint glow results, colored blue or purple by the oxygen and nitrogen in the atmosphere. The phenomenon is often considered nautical in origin because of its relatively frequent appearance on ships' masts. It is in fact named after St. Erasmus of Formiae, the patron saint of sailors (Elmo is the Italian slang). References to it in history and culture go back to the ancient Greeks; Shakespeare mentioned it in The Tempest. A popular 1985 American film called St. Elmo's Fire however, simply refers to the name of a bar.
(Note on the video: This supposedly was shot by a pilot flying at 37,000 feet in a thunderstorm near the equator.)
4. The Green Flash
It's not an especially rare phenomenon, but having the good luck to see it can be considered a rarity. And many who do witness a green flash don't realize they have. You need a setting sun over a calm, flat horizon like the ocean, and you need to really pay attention, as the green flash only shows itself for a second or two. As the sun begins to dip below the horizon the green rays at the top of its rim become visible after the red rays at the bottom have disappeared. It's refraction of light, the prism effect, aided by the appearance of a mirage on the horizon. The colors of blue and violet, which follow green in a prism, are scattered out and remain unseen to our eye, and the green is very nearly lost as well. The flash generally appears as nothing but a dot for the briefest instant. Your brain may not register what your eye has seen, but photographic evidence of the green flash abounds.
3. Kelvin-Helmholtz Waves
Even if you never see a Kelvin-Helmholtz cloud pattern in your lifetime — they are exceedingly rare — you've witnessed the principles behind their formation countless times. On a large body of water, when wind causes water at the surface to be pushed along faster than the water below, waves will form. Kelvin-Helmholtz waves are no different, they're just overhead. You need a temperature inversion to create layers of air with different densities, and an especially windy day is also required. Even then Kelvin-Helmholtz clouds are unlikely, although they make for an unmistakable sight, like a neat line of commas in the sky. The bulky name for these "comma clouds" comes courtesy of Lord Kelvin, an 18th-century physicist who has a temperature scale named after him, and Hermann von Helmholtz, a German physicist of the same era who did a lot of work in thermodynamics.
2. Raining Animals
The phrase "raining cats and dogs" does not apply here. There is no documented evidence of those animals ever falling from the sky, although pieces of what appeared to be cows are reported to have fallen to the ground in California and Kentucky in the 1800s. Most commonly, fish and frogs are the unlucky victims, giving credence to the widely accepted theory that waterspouts are usually the cause of these occurrences, which have been witnessed for millennia in nearly every part of the world. Oddly, sightings of waterspout updrafts pulling these aquatic animals up into the sky are unknown. Often the animals are dead before they hit the ground, or encased in ice, but they've also been known to be quite alert, suggesting that the distance and longevity of these events can vary widely. Showers of worms, spiders and disoriented birds are also in the historical record.
1. Poisonous Fog
Links between polluted air and health problems are well known, but it's difficult to tie any deaths to a single episode of poor air quality. There have been exceptions, however, and they're notable. During the winters of 1897, 1902, 1911 and 1930 fog combined with pollution to kill scores of people in Belgium. The Donora, Pennsylvania, smog of 1948, when a temperature inversion interacted with fumes from the town's zinc and steel plants, led to the deaths of two dozen people; mortality in the town, near Pittsburgh, was higher than in the surrounding area for years afterward. And then there was London in December 1952, when coal smoke and that city's legendary fog mixed to create a frightening black soup. Cars were abandoned on the road and people couldn't see their own feet. Over four days as many as 12,000 people died. Modern pollution controls have put an end to these disasters, at least in the developed world.
Todd Hill's first novel, Dutchess County, is now available in stores, or through Amazon.com.