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La Niña Returns, Bringing Blizzards and Misery


Lay in the rock salt. Park the snow shovel next to the door. Winter is about to get real again. That's because La Niña is back. Or at least signs suggest that she is, according to the National Weather Service. The famously frigid cold-weather pattern promises a season of chillier-than-normal weather across much of temperate North America - a jarring contrast to record warmth last winter -- and perhaps a blizzard or two before spring.


Eye in the Sky


A blizzard isn't just any bad snowstorm. An official blizzard, according to the National Weather Service, is no less than heavy snow driven by winds of at least 35 mph (56 kilometers per hour) and temperature of 20º F (-7º C) or lower.

The Real Thing

If you have doubts, consider the "Blizzard of 1888," which still holds the U.S. record. The storm hit the East Coast of the United States on a Sunday and - this is the critical factor - stalled. As it lingered it dumped 50 inches (127 centimeters) of snow on Connecticut and central Massachusetts. Howling winds piled up drifts as high has 50 feet (15 meters), burying houses and trains. Two hundred ships went down or were severely damaged between the Chesapeake Bay in Maryland and Nantucket off the coast Massachusetts. Four hundred lives were lost. Damage was estimated at $20 million.

After that, no wonder the term "blizzard" stuck. The word originally meant a canon shot or volley of musket fire. An Iowa newspaper first used it during the 1870s to describe a snowstorm. Within a few years snow blizzards were being written about in newspapers all over the United States and England.

Most East Coast blizzards, including the debacle of 1888, result from a Nor'easter, the collision of polar air moving south from Eastern Canada and the North Atlantic with warm, moist air moving north from the tropics. The lighter-weight warm air climbs up and over the cold layer and begins to cool. Water precipitating out of the cooling layer falls through the cold layer and becomes snow. Nor'easters that move along an easterly track bring heaviest snowfalls to the Eastern seaboard. If the storm moves quickly, snow falls for only six to eight hours. But if the warm air stalls against a high-pressure wall, as it did in 1888, snowfall can continue around the clock.

A similar effect causes the blizzards immediately south of the Great Lakes in late fall and early winter, when the lake waters are still warm. The "lake effect" results from the collision of cold air moving south over the still-warm lake water. The greater the difference in the temperature between the air and the water, the heavier the snowfall. Heaviest snows occur when a bitter cold front moves southeast across the Lakes.

The lake effect delivers Chicago more than its share of blizzards, but the one no one forgets moved in on a Thursday in January 1967 and lingered through the next day. The accumulation of 23 inches (58 centimeters) with 6-foot (2-meter) drifts killed 60 people, mostly men who died of heart attacks while shoveling. Some of the 75 million tons of snow removed from Chicago's streets was sent by train to children in Florida who had never seen snow before.

Major storms also tend to develop over southeast Colorado in the lee of the Rocky Mountains. Heavy snow often results as these storms move east or northeast to collide with moist air from the Gulf of Mexico.

But without a doubt the strangest blizzard in U.S. history occurred in the summer of 1816, also referred to as "The Year Without a Summer." The record cold caught people entirely off guard. The high in Savannah, Georgia on July 4 was only 46º F (7.8º C). A blizzard stunned Connecticut. Among the explanations was the eruption of Java's Tambora volcano the previous year. Dust and ash that hadn't yet settled out of the atmosphere may have shaded the Earth from the sun's warmth. But we'll never know.

On Top of the Weather

Today we would know not only the cause, but could predict when unusual weather is on the way. Satellite images allow meteorologists to track weather patterns in real time and powerful computers model its probable course. Predictions have become amazingly accurate. Long-range weather forecasting has become so sophisticated that the National Weather Service (NWS) gives a monthly update on what to expect during the next three months.

"The recent cold spell, including the ice storms, is an example of what most of the nation will likely face throughout the winter," says NWS Director Jack Kelly. "Take precautions now to prepare for winter because it's here."

The big factor is the El Niño-La Niña phenomenon. El Niño made for last winter's record warm temperatures. La Niña delivers opposite weather. The driver of these alternating weather patterns is the temperature of surface water in the tropical Pacific Ocean, which in turn alters the position of high-altitude air currents, such as the Polar Jet Stream. This river of air running west to east that separates the main body of colder, drier air to the north from warmer, moist air to the south.

The Polar Jet Stream helps create and steer storms. In warm winters, the Polar Jet Stream stays to the north. During colder winters, like the one predicted for 2000-2001, it dives south, bringing colder-than-normal weather, sometimes as far south as the Gulf of Mexico.

Other factors influence weather, says Wayne Higgins, a meteorologist with the NWS Climate Prediction Center. "However, in the absence of stronger conditions, the Polar Jet Stream will win out."

So expect cold and snow, and maybe blizzards.

But take heart. The same conditions that bring colder, snowier conditions to the north of the Polar Jet Stream make for warmer-than-normal weather to the south. If you can't tough it out until spring, there's always a vacation to Florida or the Southwest…unless a blizzard grounds your flight.

Eye in the Sky is a weekly series that brings you the story behind the headlines using satellite imagery, remote sensing, aerial photography, and maps. This feature is developed by National Geographic News with the sponsorship of the National Imagery and Mapping Agency (NIMA) and Earth-Info. Check out maps and imagery at http://www.earth-info.org.



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More Information
• In an official blizzard, winds over 35 mph (56 kilometers per hour) drive snow, reducing visibility to near zero.
• Rapidly forming winter storms called "bomb cyclones" have delivered some of the Atlantic Coast's worst blizzards.
• Approximately 70 percent of annual snowfall in most of the United States occurs during December, January and February. However, March and April are snowiest months for the eastern slopes of the Rocky Mountains.
• Buffalo, NY, is the snowiest big city in the United States, averaging 94 inches (239 centimeters) annually.
• The amount of water in 10 inches (25 centimeters) of fresh snow varies from as little as 0.10 inches (0.25 centimeters) to as much as 4.0 inches (10 centimeters).


More Information
Blizzard Survival

The first rule of blizzard survival is to stay inside and stayed tuned to weather reports.

The human body is no match for wind-driven snow in temperatures below 20º F (-7º C). Prolonged exposure can lead to frostbite or life-threatening hypothermia. Wind and gusts that accompany a blizzard can knock down trees and power lines.

Heavy snow can collapse roofs. Extreme cold following blizzards can burst pipes in homes without insulation or heat and jam rivers with ice, causing floods.

Blizzards are most dangerous for males over 40, who are at risk of heart attack while shoveling snow. Infants and people over 60 are the most vulnerable to hypothermia.

If you get stuck in your car, run the motor and heater for ten minutes every hour, but crack the window to avoid carbon monoxide poisoning.

Check to make sure the exhaust pipe isn't blocked with snow. Frequently exercise arms, legs, fingers and toes to keep blood circulating.

If you lose power in your home, close off unneeded rooms, stuff towels or rags in the cracks under doors, and cover the windows at night.

If you live in a blizzard-prone area, keep a flashlight and extra batteries, a battery-powered radio, water, and high-energy food that does not require cooking, such as dried fruit or candy on hand. If there's a baby or ill person in the house, also maintain several days' supply of medicines and other needed items.