THE GIUNESS BOOK OF AMAZING NATURE: SNOW STORMS.
HAIL is a form of precipitation comprised of ball-shaped ice particles, or hailstones. It forms when turbulent cumulonimbus clouds create strong updrafts of wind. These clouds can rise to vast heights of 16km where temperatures are as low as -62C. At such heights, water vapour is sucked up into the cloud. Newly formed ice pellets become heavy as they collect freezing water droplets. Ice crystals acquire one coat of ice after another as the updraft tosses them around the cloud. Eventually, hailstones become too heavy for the updraft to support them in the air and they plummet to the ground. Strong updrafts cause monster hailstones.
Bullets of ice
The heaviest known hailstone weighed 1kg and fell in the Gopalganj district of Bangladesh in 1986. The USA's largest reported hailstone fell in Coffeyville, Kansas, on Sept 3, 1970. This giant lump of ice had a diameter of 19cm, weighed 757g with a circumference of 44cm. In the USA, large hailstones cause up to $25million worth of property damage every year. In Hunan province, China, on June 19, 1932, a record- breaking hailstorm killed 200 people and injured many thousands more. The highest death toll caused by a hail storm took place in Moradabad, India, on April 20, 1888. During this storm, hailstones the size of cricket balls killed 250 people and more than 1,600 sheep and goats perished. The main picture shows a man in the town of Rebenacq in the French Pyrenees repairing his roof after it was hit by hailstones the size of tennis balls.
On July 12, 1984, the German city of Munich was hit by a hailstorm which caused $1billion worth of damage and injured over 400 people. The storm lasted just 20 minutes, but in that time 70,000 roofs were torn off or badly damaged and 250,000 cars had their windows smashed by hailstones up to 9.5cm across and weghing up to 300g. Outside the city, farm animals were killed and crops attened. At the airport, 150 aircraft were wrecked.
A hailstorm that hit Alberta, Canada, on July 14, 1953, flattened crops and killed around 36,000 birds. Four days later another hailstorm hit the same area and killed a further 27,000 wildfowl.
Menace in the air
On April 4, 1977 a DC9 aircraft, descending to land through a violent hailstorm, lost engine function and crash-landed on a highway near New Hope, Georgia, USA. The hail smashed a cockpit window and caused the plane's second engine to catch fire. Sixty-eight people died.
SNOW is a solid form of water that crystallizes in the atmosphere. Whereas some parts of the world are permanently snow-covered, others experience snowfall only intermittently. Snow can become treacherous in temperate regions, where it can cause havoc to transport systems and threatens livestock. In these areas, the snow often arrives in a blizzard and departs as an avalanche or in a sudden thaw.
A blizzard is a snowstorm where wind causes drifting on the ground and extremely poor visibility. The US Weather Service denes a blizzard as a storm with winds of more than 51km/h and visibility of less than 150metres (see picture of New York below left).
On Thursday Jan 26, 1967, snow began to fall on Chicago and continued through to the early hours of Friday morning. Periodic snowfalls over the next 10 days caused havoc. An estimated 75 tonnes of snow fell on the city during the storm. Some of the snow was sent in empty rail carriages as a present to children in Florida who had never seen snow before. Fatalities are usually uncommon in winter storms, but 60 deaths were attributed to the snowstorm in Chicago that year, mostly due to heart attacks brought on from shovelling the snow.
Most brutal blizzard
Five hundred people died in a storm that traversed the entire East Coast of the USA on March 12, 1993. A meteorologist described it as `a storm with the heart of a blizzard and the soul of a hurricane'. Total damage amounted to $1.2billion.
Snow falls over every continent in the world, but in areas of low latitudes it only falls on the tops of high mountains. Snow lies on the ground whenever the air temperature is below 3C. When air temperature is near this key figure, altitude can make a surprising difference to the weather. On Nov 3, 1958, rain fell on 34th Street in New York while guards on the top of the Empire State building were making snowballs.
The Swedish historian Olaus Magnus was the rst man to study individual snow crystals in the 16th Century, but it was the German astronomer Johannes Kepler who described the six-sided symmetry of every snow crystal in a pamphlet in 1611. Snow crystals come in an innite variety of pattern and shape although they all form around a basic hexagonal symmetry. Temperature and humidity are the inuencing factors that shape snow crystals. The nature of the nuclei on which the crystal forms can also affect their composition. At Bratsk, Siberia, in 1971, snowakes measuring 30cm were recorded.
Transparent hail, less than 0.5cm in diameter, which is formed when raindrops freeze, snow flakes melt and refreeze, or when snow pellets become encased in a thin layer of ice
Hailstones formed from small cloud droplets frozen together
Avalanches occur when a change in temperature causes snow particles to loosen and slide down hill
Vision impairment brought about by the dazzle of sunlight on snow
The limit of permanent snow cover, defined by altitude or longitude
What is a white-out?
A white-out blurs normal perception in a snowstorm. Clouds appear to merge into snow and without a visible horizon the normally distinguishable contours of the landscape disappear. Multiple reflection from ice crystals and the clouds prevent shadows forming, and all sense of direction and balance may be lost.
What are snow rollers?
These are naturally occurring snowballs. They form when snow flakes are driven along the ground by the wind to form giant cylinders or balls.
What is firn?
Firn is old compacted snow. It is less white than fresh snow and because of the closely packed crystals, reflects less light, making it look like plaster.