Blizzard

A blizzard is a severe winter storm characterized by strong winds and blowing snow. The National Weather Service defines a blizzard as a large amount of falling or blowing snow with winds greater than 35 miles (56 kilometers) per hour and visibility reduced to 0.25 mile (0.4 kilometer) for at least three hours. A severe blizzard is defined as having wind speeds in excess of 45 miles (72 kilometers) per hour with temperatures of 10°F (−12°C) or lower.

Most blizzards are accompanied by heavy snowfalls and temperatures of 20°F (−6°C) or lower. The falling and blowing of fine, powdery snow during a blizzard sometimes reduces visibility to less than a few yards (meters).

Blizzards create conditions that are dangerous for motorists and pedestrians. Commerce and transportation systems typically grind to a halt and roofs may collapse under the weight of the snow. Many lives are lost in blizzards due to hypothermia, a drastic drop in body temperature; frostbite, a freezing of the skin; or overexertion while shoveling snow.

Blizzards occur mainly in Canada, the United States, Russia, and the former Soviet Republics, central and northern Europe, and central and northern Asia. The United States usually experiences one to seven blizzards per year, although some winters have recorded as many as thirty-five. Blizzards occur in the United States primarily during the months of December through March.

The blizzard of 1888

From March 10 through 14, 1888, a blizzard besieged the East Coast of the United States and set snowfall records from Virginia to Maine. The Blizzard of '88—with its combination of heavy snowfall, whipping winds, and frigid temperatures—was the most devastating weather event in the history of the northeastern United States. Throughout southern New England and southeastern New York, snowfalls averaged 40 inches (100 centimeters) or more and winds were recorded at 50 to 80 miles (80 to 128 kilometers) per hour. Temperatures hovered near 0°F (−18°C).

WORDS TO KNOW

air mass:

a large quantity of air—measuring thousands of square miles (the size of several states) across—where temperature and moisture content are fairly constant throughout.

blizzard:

the most severe type of winter storm, characterized by winds of 35 miles (56 kilometers) per hour or greater, large quantities of falling or blowing snow, and low temperatures.

frostbite:

the freezing of the skin.

ground blizzard:

the drifting and blowing of snow that occurs after a snowfall has ended.

heavy snow:

snowfall that reduces visibility to 0.31 mile (0.5 kilometer) and yields, on average, 4 inches (10 centimeters) or more in a twelve-hour period or 6 inches (15 centimeters) or more in a twenty-four-hour period.

hollow column:

a snowflake in the shape of a long, six-sided column.

hypothermia:

a condition characterized by a drop in core body temperature from the normal 98.6°F (37°C) to 95°F (35°C) or lower.

nor'easter:

a strong, northeasterly wind that brings cold air, often accompanied by heavy rain, snow, or sleet, to the coastal areas of New England and the mid-Atlantic states. Also called northeaster.

sector plate:

a star-shaped snowflake.

severe blizzard:

a blizzard in which wind speeds exceed 45 miles (72 kilometers) per hour, snowfall is heavy, and the temperature is 10°F (−12°C) or lower.

stratus:

gloomy, gray, featureless sheets of clouds that cover the entire sky, at low levels of the atmosphere.

whiteout:

a condition in which falling, drifting, and blowing snow reduces visibility to almost zero.

windchill factor:

the cooling effect on the body due to a combination of wind and temperature.

New York City, Washington, D.C., Philadelphia, and Boston—the nation's economic and political centers—were all paralyzed by the storm. Two hundred ships in coastal waters were run aground, and many of them were destroyed by winds of 60 to 75 miles (97 to 121 kilometers) per hour. Four hundred people on city streets, in the countryside, and aboard ships perished in the blizzard because of exposure to strong winds and low temperatures. Half of the fatalities were in New York City. Thousands of people were stricken with frostbite and exhaustion.

Blizzard caused by convergence of storms

The intensity of the blizzard was the result of the convergence of two low-pressure systems: one, a warm, moist air mass from the south, and the other a storm system from the west. A low-pressure system is a region of low air pressure measuring thousands of square miles in area, the size of several states, that brings clouds and sometimes stormy conditions.

The southern air mass originated on March 9 over the northern Gulf of Mexico. During the next couple of days it traveled to the northeast, through Georgia and North Carolina, to New England. On March 11 and 12, the air mass held a steady position over the coast of southern New England. At the same time, a cold northeasterly wind, called a nor'easter, blew cold air into the region.

The western low-pressure system developed on March 8 over Salt Lake City, Utah. Over the next two days it moved across Colorado and the Missouri River Valley and on to the Great Lakes region. The western system ran into the southern system over Cape Hatteras, North Carolina, and formed a monstrous storm system. The storm then headed up the coast toward New York City at 80 miles (129 kilometers) per hour.

New York City gets 22 inches of snow

By daybreak on March 12, snowdrifts several feet high made the streets impassable. Visibility was reduced to a few hundred feet. By that afternoon, no trains were entering or leaving New York City. The winds were strong enough to knock people off their feet and tip streetcars off their tracks. The pedestrian bridges into Manhattan were also closed. Several hundred determined people, however, walked between Manhattan and Long Island across a pack of ice that had floated up the East River and became trapped between the two shores.

On the morning of Tuesday, March 13, the temperature was −1°F (−18°C), and the snow was still falling. Several small fires broke out as the result of faulty heating stoves. Fortunately, firefighters were able to extinguish the blazes before they developed into major fires.

By the time the snow quit early on March 14, snowfall in New York City measured 22 inches (56 centimeters), Brooklyn was socked with 26 inches (66 centimeters), and White Plains had 32 inches (81 centimeters) on the ground. The wind continued blowing even after the snow stopped, whipping up enormous drifts.

The damage in New York City

The snowfall in New York City brought power lines to the ground and disabled the city's new telephone and electrical systems. Four workers with the New York and Harlem Railroad were killed when they tried to crash their train through a huge snowdrift. Many horses perished, buried in snowdrifts. March 12 went down in the history books as being the first weekday the New York Stock Exchange closed since its opening in 1790.

The blizzard paralyzes the region

The blizzard socked New Jersey, eastern New York, Connecticut, Vermont, New Hampshire, and other parts of New England, as well as the cities of Boston and Philadelphia. Railroad service was cut off. In parts of upstate New York, Connecticut, and western Massachusetts, 40 to 50 inches (102 to 127 centimeters) of snow fell, and drifts measured 30 to 40 feet (9 to 12 meters). In Middletown, New York, where the snow reached the second stories of buildings, residents dug tunnels across streets. In Pittsfield, Massachusetts, some houses on the main thoroughfare were entirely buried by 20 feet (6 meters) of snow.

Albany and Troy, in northeastern New York state, each received more than 4 feet of snow in just a few hours—as did Middleton, Connecticut. The site of the largest snowfall was Saratoga Springs, New York, with 58 inches (147 centimeters). Gravesend, New York, had a snowdrift of 52 feet (15.6 meters), only topped by New Haven, Connecticut's 53-foot (16-meter) snowdrift.

In Camden, New Jersey, residents were trapped in their homes by mountains of snow. Ferry service to Philadelphia was hampered by severe winds, which blew the water right out of the Delaware River. The water level was driven so low in parts of the river that loaded ferries scraped bottom. One boat full of passengers struck ground and became stranded midway across the channel.

Recent events: Catastrophic blizzards

In recent years the northeastern United States has been hit hard by winter storms. The years between 2000 and 2005 saw three record-breaking storms that were both damaging and deadly.

In 2003 the northeastern United States saw an historic blizzard. The Blizzard of 2003, which is also called the President's Day Blizzard, caused then-record snowfalls across the region. The storm caused over 40 inches of snow to fall in Garrett County, Maryland, and almost as much in parts of West Virginia.

The President's Day Blizzard of 2003 exacted a greater human toll than some major storms in the following years. The 2003 storm caused at least forty-four deaths. The effort to clean up and repair damages caused by the storm cost tens of millions of dollars.

January 2005 brought another powerful winter storm to the northeastern United States. The 2005 blizzard was one of the worst storms on record to hit the region. Heavy snows covered the eastern seaboard from Mississippi to New England. At the height of the storm, as much as three feet of snow blanketed parts of Massachusetts, which saw some of the worst of the storm.

The National Weather Service ranked the Blizzard of 2005 in the top five storms in the past 100 years. The service compared the blizzard to the catastrophic Blizzard of 1978, which caused $1 billion in damage. The temperature in Boston during the storm came within one degree of the record set by the historic Blizzard of 1888. Temperatures during that storm were logged at −2°F (−18°C).

Despite the severity of the storm, the Blizzard of 2005 did not cause the type of casualties and havoc wrought by earlier storms, like the Blizzard of 1978. This is partly due to advances in technology and forecasting, which allowed preparations for the storm to be made.

In 2006, just more than a year after the Blizzard of 2005, another powerful storm hit the northeastern and mid-Atlantic regions of the United States. The storm caused record amounts of snow accumulation. This severe storm lasted from February 11 though 13. The 2006 blizzard dumped at least a foot of snow on mid-Atlantic and northeastern U.S. cities. However, despite record amounts of snow, the storm caused relatively few casualties.

Snow accumulations for the 2006 blizzard broke records. Snowfall in Central Park in New York City was recorded at 26.9 inches, an all-time record for the city. By contrast, the destructive and famous Blizzard of 1888 caused only 22 inches of snow in the city. The 2006 blizzard caused well more than 25 inches of snow throughout Connecticut and New Jersey. The storm's low-pressure system deepened as it moved up the eastern seaboard, causing power outages in tens of thousands of homes.

Dangerous science: How blizzards happen

Blizzards form in winter when two or more air masses of different temperatures and different air pressures collide. One of the air masses must contain warm, moist air, and the other cold, arctic air. For blizzards that occur in the United States, the warm air mass comes from the southern states or the Gulf of Mexico, and the cold air mass comes from Canada.

When a cold air mass advances upon a warm air mass, the approaching cold air is called a cold front. When this happens, the cold air, being denser and heavier than the warm air, wedges underneath the warm air and forces it sharply upward. The infusion of cold air causes the temperature on the ground to drop sharply. The collision of air masses also produces strong winds because of the difference in air pressures between the two masses.

The warm air cools as it rises, and water vapor within it condenses and forms clouds. Those clouds may take the form of a low-lying layer, called stratus, or they may develop steeply upward into thunderstorm clouds.

If the temperature in the clouds drops below freezing, ice crystals form. Ice crystals can then grow into snowflakes by several methods. When the snowflakes become too heavy to remain suspended in the cloud, they fall to the ground. The combination of sudden cold temperatures, high winds, and snow results in a blizzard.

Consequences of blizzards

When a blizzard strikes, it spells danger for motorists, pedestrians, public transportation systems, communication systems, and buildings. Blizzards frequently cause auto accidents, force traffic to a standstill, strand motorists, knock out power, freeze pipes, and shut down entire cities. Airports and railroads close because travel becomes too dangerous. A blizzard's whipping winds can create snowdrifts tall enough to bury cars or even buildings. A blizzard's heavy snows can make roofs collapse. Blizzards can cause agricultural losses by killing livestock and destroying crops.

Blizzards can also claim human lives. Seven out of ten people who die in blizzards are trapped in their cars and succumb to hypothermia, which is a drastic reduction of body temperature. Others die in traffic accidents on snowy, low-visibility roads. Some motorists trapped in blizzards become unconscious or die because of dangerous fumes that enter their running car when the car's tailpipe becomes clogged with snow.

When falling, drifting, and blowing snow reduces visibility to almost zero, the condition is called a whiteout. Everything appears white, making the ground and sky indistinguishable. In such conditions, a stranded person may become disoriented and lose their way. People in whiteouts

have frozen to death just steps from their door. People have even choked to death on the blowing fine, powdery snow. Other causes of death during blizzards are frostbite and heart attacks.

A key reference to: The structure of snowflakes

While snowflakes come in a variety of shapes, they all have the same basic hexagonal (six-sided) configuration. The structure of ice crystals, the smallest units of snowflakes, is also hexagonal. This basic shape can be traced back to water molecules. Because of the electrical attraction between water molecules, they form a hexagon when they freeze.

A snowflake begins its existence as an ice crystal within a cold cloud, where ice crystals coexist with water droplets that are supercooled—meaning they remain in the liquid state below the freezing point. As an ice crystal is bounced between the bottom and top of the cloud by the wind and by currents within the cloud caused by differences in temperature, the crystal grows. This can be the result of coalescence, in which the crystal hits and sticks to supercooled water drops, or by deposition, in which water vapor molecules in the cloud freeze and stick directly onto the ice crystal. As the ice crystal grows, it bonds with other ice crystals and takes on the shape of a snowflake. When the snowflake becomes heavy enough, it falls to the ground.

Snowflakes can exist in the following forms: flat, hexagonal plates; long, six-sided columns; needles that are two hundred times longer than they are wide, or starry shapes called sector plates. When a sector plate accumulates moisture it may develop feathery branches on its arms, thus becoming a dendrite—the most distinctive and most common type of snowflake. As dendrites bounce around through a cloud they may combine with other dendrites, forming a variety of complex patterns.

The shape of a snowflake depends upon the air temperature in which it is formed. Hollow columns, for instance, form when the temperature is either below −8°F (−22°C) or between 14 and 21°F (−10 and −6°C). Sector plates form at temperatures between −8 and 3°F (−22 and −16°C) and between 10 and 14°F (−12 and −10°C). When the temperature is between 3 and 10°F (−16 and −12°C), dendrites are formed. Between 21 and 25°F (−6 and −4°C) you get needles, and over 25°F (−4°C) you get thin, hexagonal plates.

The size of a snowflake depends upon the temperature of the air as the snowflake descends. If the temperature is above freezing, the snowflake melts around the edges. This process produces a film of water, which acts like glue. Snowflakes that strike each other stick together, producing large, soggy snowflakes, 2 to 4 inches (5 to 10 centimeters) or greater in diameter. These snowflakes stick to surfaces and are heavy to shovel.

Snowflakes that descend into cold, dry air, in contrast, do not readily combine with one another. Those flakes produce dry, powdery snow on the ground that is ideal for skiing.

Cold weather is hard on humans

Low air temperatures combine with high winds during blizzards to produce the wind chill factor: the apparent temperature, or how cold it feels. For instance, when it is 0°F (−18°C) outside and the wind is blowing at 20 miles (32 kilometers) per hour, it feels like −40°F (−40°C). In low wind chills, humans are susceptible to hypothermia, which is the drop in the internal body temperature from the normal 98.6°F (37°C) down to 95°F (35°C) or lower, as well as to frostbite, which is the freezing of the skin.

The human body has little natural protection against the cold. Without the proper clothing in cold weather, a person rapidly loses body heat. Even at 68°F (20°C), an unclothed person will begin to shiver. Children and older people are the least able to withstand cold weather since their bodies regulate temperature with less efficiency than people of other age groups.

Once hypothermia sets in, a person will shiver violently and experience a gradual loss of physical and mental functions. As the body temperature continues to drop, however, the shivering will decrease, and the victim may actually feel warm. Advanced hypothermia can lead to unconsciousness and even death.

Another hazard of cold weather is frostbite: the freezing of the skin, which causes damage to tissues. There is a risk of exposed skin freezing when the wind chill is below −22°F (−30°C), and it only takes a minute or so for skin to freeze when the wind chill is below −58°F (−50°C). The parts of the body most susceptible to frostbite are the ears, nose, hands, and feet. In the mildest cases of frostbite, while complete recovery is possible, the affected area may feel numb for several months. Serious cases of frostbite can produce a long-term sensitivity to the cold. In the most severe cases, when the tissue freezes to the point that it dies, the affected limb turns black. In such cases the affected area has to be amputated.

The earliest warning sign of impending frostbite is pain in the fingers, toes, or nose. If the pain is followed by numbness, then frostbite is setting in, and it is necessary to get out of the cold immediately. If you can, run the affected area under warm water, from 105°F to 110°F (41°C to 43°C). If the area hurts as it gets warmer, this is a good sign. It means that the tissues are still alive.

Low temperatures are also hard on humans in other ways. Greater stress is placed on the heart as the outer parts of the body become cool. The heart compensates for this by working harder to pump blood to those areas. Strenuous activity, such as shoveling snow, can bring on heart attacks—especially in older people or people with histories of heart trouble.

Extreme weather: The New England blizzard of 1978

On February 6-7, 1978, southeastern New England suffered its most disruptive snowstorm of the century. The snow was produced by a low-pressure system that remained stationary for more than twenty-four hours just off the eastern tip of Long Island. At the same time, a strong, northeasterly wind known as a nor'easter blew in from southern Canada. The snowstorm, which came just seventeen days after a previous blizzard, claimed at least fifty lives. Most of the deaths were due to overexertion while shoveling snow.

Over a thirty-hour period, heavy snow fell on the upper Chesapeake Bay area, Long Island, parts of eastern Massachusetts, central Rhode Island, eastern Connecticut, Vermont, and New Hampshire. Both Boston and Providence received more than 3 feet (0.9 meter) of snow. Some parts of Rhode Island reported 4 feet (1.2 meters) of snow. The storm also brought significant snowfall to New York City, New Jersey, and eastern Pennsylvania.

The weather paralyzed traffic, caused power outages, and forced businesses to close in Rhode Island, Connecticut, and Massachusetts for the better part of a week. President Jimmy Carter declared emergencies in those three states. In many parts of New England driving in nonemergency cases was banned, and violators were slapped with hefty fines.

Gale-force winds shook much of the region during the storm. A gust measuring 79 miles (127 kilometers) per hour was reported at Boston's Logan Airport, with a two-day wind-speed average at the airport of 30 miles (48 kilometers) per hour. Hurricane-force winds greater than 74 miles (119 kilometers) per hour blasted Massachusetts' eastern shore. Those winds combined with high tides to produce colossal waves that smashed into coastal communities. More damage was caused by coastal flooding during that storm than from any hurricane affecting New England to that date.

More than one thousand army troops from the Midwest and the South were flown to New England to assist in the cleanup from the storm. Over 140 military aircraft, carrying nearly 7 million pounds (3.2 million kilograms) of snow-clearing equipment, landed at airports in Boston, Providence, and Hartford, Connecticut, for use in the effort.

Are humans causing blizzards?

The Blizzard of January 1996, which produced record-breaking snowfalls on the East Coast and caused more than one hundred deaths, made some scientists wonder if global warming was bringing on strong blizzards and other types of extreme weather. Many scientists agree that global average temperatures have begun to rise and will continue to rise, because of an increase of certain gases in Earth's atmosphere. According to the U.S. Environmental Protection Agency (EPA), global average temperatures have increased by 1°F (0.5°C) in the last century. Much of this global climate change, especially during the last fifty years, may be due to human activity.

Human activities have caused the build-up of greenhouse gases in Earth's atmosphere. These gases are called greenhouse gases because they let sunlight come in but don't let heat go back out into space—as if Earth were covered with a big glass greenhouse that keeps everything warm. The most plentiful greenhouse gases are water vapor and carbon dioxide. Other greenhouse gases include methane and nitrous oxide.

The increase of carbon dioxide in the atmosphere is believed to be the main reason for global warming. Carbon dioxide is produced by burning fossil fuels, such as coal, fuel oil, gasoline, and natural gas, and is emitted into the air by homes, factories, and motorized vehicles. During the last century, the amount of carbon dioxide in the atmosphere has increased by 30 percent. During that same period, the planet has become, on average, slightly more than 1°F (0.5°C) warmer.

There doesn't seem to be much doubt that humans have affected global warming by burning fossil fuels and other activities, but is that activity making blizzards more frequent and more intense?

Some say yes; others no

Some scientists say global warming causes more water to evaporate from the oceans into the atmosphere. When this warmer, moister air collides with colder air, it can produce more ice crystals and stronger winds, which can result in stronger blizzards. They also say that because this evaporation process is going on all the time, it also produces a steady supply of moist air, which can result in more frequent blizzards.

Other scientists point out that global warming should also warm the colder regions and therefore produce less cold air to collide with the warm, moist air. This should produce fewer blizzards, they claim. They also note that in many areas, no real increase in the amount of moisture in the air has occurred. These scientists claim that although global warming is real, it has not resulted in more frequent or more intense blizzards.

Technology connection

There are many ways to predict, prepare for, and respond to blizzards. Today's weather forecasters use satellite images, radar, data from weather stations on the ground, and computer models to determine where and when blizzards are forming.

In blizzard-prone regions, residents attempt to lessen the impact of the storms by erecting snow fences, which reduce drifts on roads. They also maintain fleets of snowplows for snow removal, stock salt for melting ice, and stock sand for providing traction on slippery roads. When a blizzard starts, snowplows and salt and sand spreaders are dispatched to keep roads open—at least for use by emergency vehicles.

Weather satellites

Weather satellites, circling the globe in space, provide meteorologists with pictures and other information about blizzards and other storms. The first weather satellite, called TIROS 1 (Television Infrared Observation Satellite), was launched in April 1960. Today, several nations operate satellites that continuously monitor global weather.

For most people, the words "weather satellite" conjure up images of swirling clouds that are seen on television newscasts. While weather satellites do produce those photos, they also perform other functions. Weather satellites determine the temperature throughout the atmosphere, from the cloud tops down to the land and oceans. They also measure humidity and wind speeds in the upper air and even track plumes of invisible water vapor. Weather satellites give meteorologists their first look at blizzards and other storms forming over land or sea. Once a developing storm is spotted, it is probed in greater detail using Doppler radar located on the ground.

Doppler radar

Doppler radar is a sophisticated type of radar that relies on the Doppler Effect—when a wave, like a radio wave, bounces off a moving object, it changes the frequency of the wave. Scientists use this technique to determine wind speed and direction, as well as the direction in which precipitation is moving. Radar, which is an abbreviation for "radio detection and ranging," works by emitting short radio waves, called microwaves, that reflect off clouds and raindrops. This information allows forecasters to identify potential blizzards in their earliest stages.

In 1996 a network of 156 high-powered Doppler radars, called NEXRAD (Next Generation Weather Radar), was installed across the United States. Data from these radars around the nation are sent, via high-speed computers, to National Weather Service (NWS) centers and field offices around the country. At the NWS' Storm Prediction Center in Norman, Oklahoma, meteorologists analyze weather data from Doppler radars and other systems twenty-four hours a day. When they detect conditions that could give rise to winter storms, they notify the weather center in that area. The local weather center may then issue a winter storm alert.

Extreme weather: The great Midwest blizzard of 1967

One of the largest blizzards on record for the Midwest came on January 26-27, 1967. The storm of snow and ice affected central and northern Illinois, central and northern Indiana, southeast Iowa, lower Michigan, Missouri, and Kansas. Kalamazoo, Michigan, received 28 inches (71 centimeters) of snow. Gary, Indiana, and Chicago, Illinois, both reported 24 inches (61 centimeters).

The blizzard was produced by a storm system that formed over the Gulf of Mexico and traveled north to the Ohio River Valley. The system had brought unseasonably warm weather to the Midwest in the five-day period prior to the blizzard. Then on January 24, just two days before the blizzard, a cold air mass arrived from the North. The combination of warm and cold air produced severe thunderstorms and tornadoes. The tornadoes tore through Missouri, Illinois, and Iowa. They killed several people and damaged or destroyed 200 houses.

On January 26 the weather changed sharply in Chicago. While lightning still flickered in the sky, the temperature dropped and the wind picked up. Snow began falling and a blizzard was soon underway. A record-setting 24 inches (61 centimeters) of snow fell in a little more than twenty-nine hours. Winds clocked at 50 miles (80 kilometers) per hour, and gusting to 60 miles (97 kilometers) per hour, piled up snowdrifts 20 feet (6.6 meters) high. There were seventy-six deaths due to the storm, most of them in Chicago.

Chicago remained at a stand-still for several days under 24 million tons (22 metric tons) of snow. The city was a tangled mass of stranded cars, taxicabs, and trucks. More than three hundred city buses and even some snowplows were among the stalled vehicles. The city's expressways looked like huge parking lots. Long-distance and commuter train service was suspended. Chicago's O'Hare Field (now O'Hare International Airport), one of the busiest airports in the world, was closed for a record three days.

In central Illinois, central Indiana, Missouri, and Kansas the snow, plus sleet and freezing rain, brought down power lines and put much of the region in a blackout. National Guardsmen were called out to help with snow removal in Indiana.

Computer-based prediction

Computer-based prediction relies on a sophisticated computer program called a numerical prediction model. The model incorporates mathematical equations that mimic processes in nature. When data from weather instruments is entered into a computer, the program projects how the weather will change over the next twelve hours, twenty-four hours, forty-eight hours, and several days into the future.

Due to improved computer forecasting models in recent years, the amount of time between when a blizzard warning is issued and when the storm strikes has greatly increased. In fact, major storms can now be predicted by computer even before their associated conditions are detected by weather stations.

Snow fences

Snow fences are devices that slow winds and reduce the blowing and drifting of snow. They are erected along highways to reduce the amount of snow that ends up on the road. As the wind whips across a clearing, it picks up snow. When the snow-laden wind hits a snow fence, it slows down. The wind then deposits its snow, forming a gradual drift on the other (downwind) side of the snow fence.

A snow fence must be placed far enough from the road to allow room for the snowdrift to form, without reaching the road. The rule of thumb is that snow will accumulate downwind of the fence for a distance approximately ten times the height of the fence. Therefore, if a fence is 10 feet (3 meters) high, it should be placed at least 100 feet (30 meters) from the road.

Salting icy roads

Salt is applied to snowy, icy roads because it melts ice and prevents the water from refreezing. Salt is also relatively cheap and easy to apply, making it the de-icing agent of choice since the 1960s.

Sodium chloride (NaCl), the type of salt used on roads, melts ice through an equilibrium change. Ice on the ground is in a state of dynamic equilibrium between the liquid and the solid states. When sodium chloride comes into contact with the ice, it is dissolved. When dissolved, sodium chloride breaks down into one positively charged sodium ion (Na+) and a negatively charged chloride ion (Cl−). At the same time it causes the water molecules making up the ice to disassociate into one hydroxide ion, OH−, and one hydronium ion, H+. The positively charged hydrogen atoms are drawn to the negatively charged chloride atoms, and negatively charged oxygen atoms are drawn to the sodium atoms.

The sodium and chloride ions bond with the hydronium and hydroxide ions so that hydronium and hydroxide are not free to recombine into water. The sodium and chloride ions also draw water molecules away from one another. Salt, in this way, both prevents liquid water molecules from forming ice crystals and breaks up existing ice crystals. The speed of melting is increased, while the speed of freezing is not changed. Sodium chloride is only effective at melting ice at temperatures down to 20°F (−7°C).

Whereas salt provides an efficient means of melting snow and ice on roads and has greatly contributed to highway safety, it also has a downside. Salt is bad for the environment. It kills vegetation along the side of the road and can seep down into wells, making the water undrinkable. Salt also causes vehicles to rust and bridges to corrode. For these reasons, salt is applied only in the minimum quantities necessary to get the job done.

Experiment: Freezing salty water

Normally, water freezes at 32°F (0°C). However, salt can be used to lower the freezing point of water. This is why some communities throw salt on roadways during winter storms. To demonstrate how this works, take two cups of water of the same size. The water should be the same temperature. Place a tablespoon or so of salt in one of the cups and place both cups in the freezer. Then check each cup every ten minutes or so. You'll see that the cup of plain water freezes before the cup of salty water. This is because a chemical reaction between the salt and the water lowers the water's freezing point. You can vary this experiment by doing more trials in which you add more or less salt. The more salt you add, the colder the water will have to become before it freezes.

A matter of survival

The National Weather Service issues blizzard warnings whenever blizzard conditions are expected. If forecasters predict a winter storm that is less severe than a blizzard, but still serious enough to create dangerous travel conditions, they will issue another type of winter storm alert. Four classes of winter storm alerts, based on the seriousness of the storm, are defined as follows:

• A winter weather advisory states that snow, sleet, freezing rain, or high winds may be on the way. It advises people to exercise caution when traveling.
• A winter storm watch states that at least 6 inches of snow and an ice storm may be on the way. It advises people to limit their travels and to exercise great caution if they must venture onto the roads.
• A winter storm warning states that a storm, including heavy snow and possibly ice, has already begun or will soon begin. It advises people not to travel, except in an emergency.
• A blizzard warning states that a blizzard—including blowing or falling snow, low temperatures, and winds of at least 35 miles (56 kilometers) per hour—is on the way. The combination of moving snow and low clouds make it appear that the ground and sky are a continuous white sheet (called a whiteout), making travel nearly impossible. It advises people to remain indoors.

Reports from the past: Tragedy at Donner Pass

One of the most famous blizzard-related tragedies in history occurred during the winter of 1846–47 in the Sierra Nevada Mountains of California. A group of eighty-seven pioneers, including men, women, and children, left Illinois for California in April 1846. The group, led by George and Jacob Donner, was known as the Donner Party.

On October 31, the Donner Party began their ascent into the mountains in northeastern California. When they reached a pass (today called Donner Pass) at an altitude of 7,085 feet (2,160 meters), the snow and wind forced them to a halt. A few members of the party pressed on to seek help, while the others erected shelters and prepared to wait for better weather.

The snow and wind relentlessly blasted the pioneers in the mountain pass. Some drifts reached 60 feet high. "We cannot see twenty feet looking against the wind," Donner Party member J. F. Reed wrote in his diary, "I dread the coming night."

Before long the group's food supplies ran out. The oxen they had planned to kill and eat had become lost in the snowstorms. For a time the pioneers lived on mice and twigs; then the winter became so severe that people dared not venture outside. Forty people died of disease or starvation in the following months. In time, the survivors became so desperate and addled by starvation that members of the party resorted to eating their own dead. Food supplies were finally brought to the trapped group in February 1847 after the men who had gone for help finally reached the Sacramento Valley and organized a rescue party.

Today a major highway and railroad tracks connecting San Francisco with Reno, Nevada, run through the Donner Pass. The Donner Memorial State Park was erected near the pass to commemorate the pioneers who lived and died through that terrible winter.

Preparing for blizzards

If you live in an area affected by winter storms, it is wise to take the following precautions at the start of the season:

• Store extra blankets and warm clothing and boots for every member of the family.
• Put together a supplies kit for your home containing first aid materials, a battery-powered flashlight, a battery-powered radio, extra batteries, nonperishable food, a nonelectric can opener, and bottled water.
• Store a similar supplies kit in the trunk of your car, plus a shovel, a bag of sand, tire chains, jumper cables, and a piece of brightly colored cloth to tie to your antenna.
• Keep your car's gas tank full to prevent the fuel line from freezing.

Tips for outdoor survival

If you must go outside during a winter storm, follow these rules:

• Be aware of the current temperature and wind chill. When dangerous conditions are present, only venture out for short periods.

• Wear several layers of lightweight clothing, mittens, a warm hat with ear flaps, a scarf covering your face and neck, warm socks, and waterproof boots. Wear wool clothing closest to your skin. (Wool will trap your body heat even if it gets wet.) Wear a brightly colored coat.
• Don't venture out alone.
• Walk carefully over icy ground.
• When shoveling snow, take frequent breaks to avoid overexertion.
• If you must drive, inform someone of your route, destination, and expected time of arrival.
• Stay away from downed wires—they can cause burns or electrocution. Report downed wires to the power company.
• If you're trapped outdoors in a blizzard, dig a large hole in the snow and climb in. This "snow cave," as it is called, will protect you from the wind and decrease the rate at which your body loses heat.

Surviving a blizzard in your car

If you get stranded in your car during a blizzard, follow these rules:

• Stay with your car. Tie the brightly colored cloth to your antenna so rescuers can spot you. Don't attempt to walk away! It's easy to become disoriented and lose your way in a snowstorm.
• Only start the car and turn on the heater for ten minutes out of every hour. When the car is running, leave on the inside light so you can be spotted. When the car is not running, periodically check the tailpipe and clear it of snow, if necessary. If your tailpipe is blocked, dangerous exhaust fumes can back up into the car.
• Move your arms and legs continuously to stay warm and maintain your blood circulation.
• Let in fresh air by slightly opening the window that's opposite the direction of the blowing wind.

[See AlsoForecasting; Precipitation; Weather: An Introduction ]

For More Information

BOOKS

Allaby, Michael. Blizzards. 2nd ed. New York: Facts on File, 2003.

Cable, Mary. The Blizzard of '88. New York: Antheneum, 1988.

Erlbach, Arlene. Blizzards. Chicago: Children's Press, 1995.

Hopping, Lorraine Jean. Blizzards! New York: Scholastic Inc., 1998.

Rosenfeld, Jeffrey P. Eye of the Storm: Inside the World's Deadliest Hurricanes, Tornadoes, and Blizzards. New York: Basic Books, 2005.

WEB SITES

Blizzard of 1996. National Snow and Ice Data Center. 〈http://nsidc.org/snow/blizzard/〉 (accessed August 17, 2006).

Historical Winter Storms. The Weather Channel. 〈http://www.weather.com/encyclopedia/winter/history.html〉 (accessed August 17, 2006).

Northeastern Regional Climate Center. 〈http://www.nrcc.cornell.edu/〉 (accessed August 17, 2006).

USA Today Weather. USA Today. 〈http://asp.usatoday.com/weather/weatherfront.aspx〉 (accessed August 17, 2006).

bliz·zard / ˈblizərd/ • n. a severe snowstorm with high winds and low visibility. ∎ fig. an overabundance; a deluge: a blizzard of legal forms.

blizzard A storm of blowing snow with high winds and low temperatures. Blizzards are a notable climatic feature of the northern and central parts of the USA in winter, and are related to depression tracks. In the USA, a blizzard is defined by the National Oceanic and Atmospheric Administration (NOAA) as a storm with winds of at least 56 km/h, temperatures below −6.7°C, and enough falling or blowing snow to reduce visibility to less than 0.4 km. In a severe blizzard, wind speed is at least 72.5 km/h, temperatures below −12.2°C, and visibility is close to zero.

blizzard A storm of blowing snow with high winds and low temperatures. Blizzards are a notable climatic feature of the northern and central parts of the USA in winter, and are related to depression tracks. In the USA, a blizzard is defined by the National Oceanic and Atmospheric Administration (NOAA) as a storm with winds of at least 56 km/h, temperatures below −6.7°C, and enough falling or blowing snow to reduce visibility to less than 0.4 km. In a severe blizzard, wind speed is at least 72.5 km/h, temperatures below −12.2°C, and visibility is close to zero.

blizzard XIX. of unkn. orig. (first (U.S.) senses ‘sharp blow’, ‘shot’).