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  To understand the movement of water, to understand weather, one has to appreciate the earth for what it is: a spinning round ball with a rough surface. If the world were flat, facing the sun, receiving equal amounts of sunlight across every square inch, it would be a simpler place. It is not flat. It is a sphere. A square foot of sunlight hitting the equator at noon spreads out across a square foot of the earth’s surface, while a square foot of sunlight hitting the earth near the poles, where the globe curves away and the earth’s surface is turned at an angle to the sun, spreads out over two square feet or three square feet or ten square feet of the earth’s surface, depending on where one stands. The square foot of light and heat and sustenance that hits the ground at the equator has to be shared across those multiple square feet at higher latitudes.

  Air at the equator, warmed by the sun, rises. Rising air leaves behind an area of low pressure — a low, as it is called. Wind blows from areas of high pressure to areas of low pressure, performing the singular role of restoring equilibrium, of preventing too much air from piling up in any one place. But in fulfilling this role, wind transfers heat. Near the surface of the earth, air rushes in to fill the low, replacing the warm air that has risen. The new air itself warms under the tropical sun and rises. More air is sucked in. Meanwhile, the rising hot air spreads out as it gains altitude. In spreading out, its pressure drops, and the heat contained in the air mass spreads out too, making the air mass cooler. The drop in pressure is accompanied by a drop in temperature. The whole mass spills outward from the equator. Along the way, water vapor carried in the air mass grows cool enough to condense and tumble downward as liquid water. Around the latitude of Shanghai and Jacksonville in the Northern Hemisphere and Easter Island and Cape Town in the Southern Hemisphere, and moderated by local geography and the myriad factors that affect air movements, it tumbles down. George Hadley imagined these global patterns in 1735, before satellites, before computers, before reasonable maps of the world. The global loops of rising and cooling air near the equator became known as Hadley cells. Farther north, similar patterns of rising and falling air became known as Ferrel cells and Polar cells.

  The earth, spinning, moves beneath the air above it. The air — cycling up and down in Hadley cells and Ferrel cells and Polar cells, then spilling out north and south in what should be a straight line — is turned by a spinning earth. In the Northern Hemisphere, the earth’s spin tends to move wind to the right of its direction of travel. In the Southern Hemisphere, the earth’s spin moves wind to the left of its direction of travel. This effect, this odd rightward and leftward trending of moving air, was described in 1835 by the Frenchman Gaspard-Gustave de Coriolis and has become known as the Coriolis effect.

  But the earth is rough, with mountains and valleys and their attendant shadows. Here on the southern slopes of this mountain, the sun bathes the earth in warmth, but there in that shadowed valley, the earth is cool. And the ground itself is patchy. Here on this dull patch of bare dirt, sunlight warms the soil, while there on that patch of snow — on that patch of crystalline water turned white and smooth to form what amounts to the closest thing nature offers to a perfect reflector — the warmth bounces off, back into the sky. Under this clear blue sky, the heat is lost, reflected back into space. There under that cloud, the heat is trapped, held in by a blanket of dust and moisture. This shoreline warms quickly under the morning sun, sending its air skyward, and the air above the ocean or lake or river blows shoreward to fill what would otherwise become a vacuum. The air above that black roof is hot, and when it moves skyward, it sucks in air from around the yard, which then is heated and sent skyward, too. The air is heating and cooling and tumbling about, cells within cells within cells, none of it standing still for very long, all of it moving with a Coriolis twist.

  Even within the simplicity of Hadley cells and Ferrel cells and Polar cells, ignoring the spinning earth and the irregularities of mountains and reflections from snow, local complexities arise. Superimposed on the simplicity of global patterns is the nature of fluid dynamics. High in the atmosphere, where warm and cold air meet, vortices form, like the eddies and whirlpools of fast-flowing rivers, spinning around themselves and floating downstream, confusing the eye by combining directional motion with spinning and chaotic dancing. The eddies become regions of low pressure, depressions that must be filled. They suck in air and moisture, pulling it skyward, and high in the sky condensing damp air to rain or snow or sleet or hail and then tossing it back to the earth.

  Wind moves frigid air to warmer climes. It creates blizzards that trap schoolchildren on the prairie. It creates raging gales into which people walk or sail or ski. It picks up snow that sand-blasts bark from trees.

  In the end, weather can be described as a mishmash of events, each one alone predictable, but intermingling to compound one another and confuse the issue, and in the end adding up to nothing less than a complex mess of unpredictability.

  The ancient Babylonians said, “When a halo surrounds the sun, rain will fall. When a cloud grows dark in the sky, the wind will blow.” Before Socrates, Thales of Miletus made a weather calendar. Aristotle commented on clouds, dew, snow, and hail, recognizing that they differ because of temperature. The barometer was invented in 1643 and the anemometer, for measuring wind speed, in 1667. Ben Franklin realized that the weather in Philadelphia came from somewhere else and left for somewhere else. His attempts to observe a lunar eclipse in 1743 were foiled by storm clouds, but his friends in Boston watched the eclipse and then, four hours later, watched his storm clouds roll in.

  By 1846, weather reports transmitted by telegraph could be purchased for between twelve and twenty-five cents a day. During the Crimean War, the warship Henri IV was lost in a storm on November 14, 1854, and Urbain Leverrier, director of the Paris Observatory, urged the French government to recognize the need for improved weather forecasting. A year later, in the United States, the Smithsonian was posting weather maps in its Great Hall. Networks of weather reporters — some paid, some amateurs — sent information on local conditions to central repositories. A man wearing a raincoat and carrying an umbrella might sit on a park bench in the city, studying the contents of a rain gauge, while another might record temperatures on Texas rangelands from the back of his horse. A third might measure the wind blowing in off a busy harbor, and a fourth might record the presence of morning dew on his cornfield. And then, with all of these observers working, with all of them piping in information through more than twenty thousand miles of telegraph wires, Adolphus Greely, not long back from the Arctic, failed to effectively foresee the Blizzard of 1888, the School Children’s Blizzard, predicting instead a cold wave with snowdrifts. The failure left nineteen-year-old Etta Shattuck alone for three days, bivouacked in a haystack, singing hymns and praying while the storm raged, saved from the haystack only to die from the infections that followed frostbite. The failure left a seventeen-year-old girl frozen to death standing up. Because of the failure, the bodies of the Kaufmann brothers, who died huddled like penguins trying to stay warm, had to be thawed in front of a woodstove before they could be separated.

  Vilhelm Bjerknes, a Norwegian working at the beginning of the twentieth century, was the first to propose the application of thermodynamics and fluid mechanics to the atmosphere. His thoughts evolved to rely on a system of cells, stacked one above the other and covering the entire earth in nothing less than a three-dimensional checkerboard. The idea was to populate the three-dimensional checkerboard with data from observations and then use the data to predict what would happen next.

  During World War I, the English meteorologist Lewis Fry Richardson tackled the rat’s nest of calculations needed for numerical forecasting. In 1922, he published a book saying that the calculations would require sixty-four thousand people working day and night to keep up with the weather. He envisioned a city of workers in a building laid out to mimic the globe itself, with each of the workers struggling through his equations in a space representing his part
of the globe. There would be green space outside, soccer fields and lakes. Those who predicted the weather, Richardson believed, should have the opportunity to experience it. In the end, though, the city was never built. It turns out that this decision was justified. Had the city been built, it would have failed in its purpose, doomed from the outset by a naive belief in a strictly deterministic universe.

  The Americans were the first to use electronic computers in weather prediction, in the 1950s. The data, one might think, would be adequate: more than ten thousand weather stations check conditions around the globe, another five thousand ships and planes send in information, unmanned buoys transmit data from remote reaches of the world’s oceans, more than a thousand weather balloons go up each day to sample the sky, and satellites circle endlessly with their gaze turned back toward earth. But the data are not adequate. In 1963, Edward Lorenz set up weather models on a computer. He compared models run with data offering three decimal points of accuracy and those run with data offering six decimal points of accuracy. The results were completely different. Tiny differences in the starting point resulted in major differences at the end point. It would be comparable to a banker counting his wealth in dollars and in pennies, only to discover that he was well positioned in dollars but flat broke in pennies. It made no sense. It led to what was later called chaos theory. Lorenz delivered a talk to the American Academy for the Advancement of Science titled “Predictability: Does the Flap of a Butterfly’s Wings in Brazil Set Off a Tornado in Texas?” The answer: yes. Or at least it might.

  In medieval times, weather predicting was an occult art. Forecasters were burned at the stake.

  It is January ninth and twenty below at the Anchorage airport, close to the record cold set in 1952. The ground hides under four feet of snow, with plowed piles and drifts running deeper. Long icicles hang from roofs. El Niño, where have you gone?

  I head south. By the time I fly over the Canadian border, temperatures on the ground are above forty. They hover in the forties for more than a thousand air miles, and then, as abruptly as a color change on a weather map, they reach the fifties. And by the time I land in New Orleans, the mercury flirts with seventy. I have flown across almost ninety degrees of temperature change.

  For the most part, the flight path, at thirty thousand feet, took me through the troposphere. Puffy white cumulus clouds call the lower troposphere home. Cumulonimbus clouds can start down at the level of cumulus clouds, but they tower skyward as much as six miles, with updrafts that send pellets of water screaming toward space, turning to ice or snow as the air cools, then plummeting back down — not drifting down with gravity, but flushing down in rushed gusts. They roller-coaster up and down, sometimes freezing and thawing repeatedly, maybe eventually breaking loose to parachute to the ground as rain or snow or ice or undecided sleet. A cumulonimbus cloud can hold five hundred thousand tons of water.

  For every mile upward in the troposphere, for every mile farther from the earth’s surface, the temperature drops seventeen degrees, plummeting to 65 below. But then it rises again in the stratosphere, warming up to the freezing point in the blanket of ozone that drifts around between nine and twenty-five miles up. Beyond, it cools back down. Around the fifty-mile mark, near what most would consider the edge of space, the thermometer drops to 180 below. At this temperature, carbon dioxide freezes solid. A few miles farther up, where the northern lights dance but still well below the realm of weather satellites and space shuttle orbits, the temperature rises. It exceeds 1,000 degrees, hot enough to melt lead and zinc, but in air so thin that it does not matter, in air so thin that it is not worthy of the name.

  A hundred and fifty years ago, in England, not far from Westminster Abbey and Windsor Palace, a man named James Glaisher amused himself by sketching snowflakes. Not satisfied with what he found on the ground, he strapped a basket to the bottom of a balloon, loaded the basket with a drawing pad and an assistant, and rode it upward. In warmer clouds, reasonably close to the earth and ripe with humidity, Glaisher sketched the star-shaped flakes of Christmas cards. As he went higher, the air cooled. His assistant grew cold. The assistant’s hands, in particular, were chilled. Glaisher pressed on. The assistant, his loyalty guaranteed by the absence of any reasonable alternative to staying in the basket, stood by his side. Glaisher sketched hexagonal crystals of snow at five degrees above zero and column-shaped flakes at fifteen below. At twenty-nine thousand feet, in very thin air, Glaisher collapsed. The basket swung wildly beneath the balloon. Glaisher’s assistant tried to release gas from the balloon, but his freezing hands were too stiff to pull the dump cord. He gripped it in his teeth and pulled. Gas flowed out of the balloon, and both men survived.

  Glaisher wrote of the snowflakes he had seen: “Their forms are so varied that it seemed scarcely possible for continuous observations to exhaust them all.”

  I amuse myself on the airplane with a collection of quotations about weather lore:

  A bad winter is betide,

  If hair grows thick on a bear’s hide.

  If onions are more abundant than bears, there is this:

  Onion skins very thin,

  Midwinter coming in;

  Onion skins very tough,

  Winter’s coming, cold and rough.

  Or this gem about February second, Candlemas Day, still three weeks off:

  If Candlemas Day be fair and bright

  Winter will have another fight.

  If Candlemas Day brings cloud and rain,

  Winter won’t come again.

  In 1776, a son of the parish clerk of Bampton in Devon, England, was killed by an icicle that plummeted from the church tower and speared him. His memorial:

  Bless my eyes

  Here he lies

  In a sad pickle

  Kill’d by an icicle

  On August 16, 1970, a chunk of ice fell from an airplane and crashed through the roof of a home just outside London. On March 25, 1974, ice eighteen inches across slammed into the hood of a woman’s car, again near London. She was later compensated by an airline. In March 1978, Chicago police sealed off roads around the city’s tallest buildings while ice, accumulated during a storm, crashed to the sidewalks.

  On March 7, 1976, in Virginia, a basketball-size chunk of ice crashed into a roof, but this time there were neither airplanes nor skyscrapers anywhere in the vicinity. On June 4, 1953, in southern California, fifty lumps of ice fell, weighing in total about a ton and with individual pieces as heavy as an adult man. Farther back, on August 13, 1849, a block of ice nearly seven feet in diameter fell in Scotland. According to an 1849 issue of the Edinburgh New Philosophical Journal,

  a curious phenomenon occurred at the farm of Balvullich, on the estate of Ord, occupied by Mr. Moffat, on the evening of Monday last. Immediately after one of the loudest peals of thunder heard there, a large and irregular-shaped mass of ice, reckoned to be nearly 20 feet in circumference, and of a proportionate thickness, fell near the farm-house. It had a beautiful crystalline appearance, being nearly all quite transparent, if we except a small portion of it which consisted of hailstones of uncommon size, fixed together. It was principally composed of small, square, diamond-shaped stones, of from 1 to 3 inches in size, all firmly congealed together. The weight of this large piece of ice could not be ascertained; but it is a most fortunate circumstance, that it did not fall on Mr. Moffat’s house, or it would have crushed it, and undoubtedly have caused the death of some of the inmates. No appearance whatever of either hail or snow was discernible in the surrounding district.

  The May 1894 Monthly Weather Review reported an ice-encased gopher turtle falling during a hailstorm in Bovina, Mississippi, and in December 1973, a newspaper reported frozen ducks falling in Stuttgart, Arkansas.

  And then there is snow. The journal Nature reported three-and-a-half-inch flakes from a 1997 storm. In January 1915, snowflakes three and four inches across fell on Berlin. According to the Monthly Weather Review of February 1915, the flakes “resembled a ro
und or oval dish with its edges bent upward.” And on January 28, 1887, a report from Montana described flakes — “flakes” in this case perhaps an odd choice of word — fifteen inches across and eight inches thick.

  The chaos of weather spills over with freakish events. But it is usually the merely unusual ones, not the freakish, that make history. There is, for example, nothing freakish about hail. It forms regularly in cumulonimbus clouds, with little balls of water and ice riding winds skyward, reaching altitudes beyond the realm of jet planes and temperatures of one hundred degrees below zero, often falling and rising many times, buffeted by the internal chaotic gales of cumulonimbus thunderheads, but finally falling from the sky.

  There are records of freakishly big hailstones: A 1697 hailstorm in England dropped four-inch hailstones that killed at least one person. A hailstone in Kansas weighed just under two pounds. The largest recorded hailstone, weighing more than two pounds, fell in 1896 in Bangladesh. But it is the lesser hailstorms that leave historical footnotes: A hailstorm in April 1888 killed 246 people in India. In April 1977, a hailstorm took out the engine of an airplane and smashed its cockpit window, killing 68 people after a crash landing on a Georgia highway. And in 1984, a hailstorm caused well over a billion dollars’ worth of damage in Munich.