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.