Forecasts: Signs of Clearing

March 21, 1993|By DOUGLAS BIRCH

The Blizzard of '93 slathered the Atlantic coast in 10 to 50 inches of snow, scattered record lows from Florida to upstate New York, fanned winds up to 110 mph, poured a quick-freezing mix of snow and hail on Baltimore, blocked interstate highways, sank ships and caused at least 193 deaths.

It was a monster, a killer, a once-in-a-century snowstorm. But it did a lot less damage than it might have because people had plenty of time to get out of its way.

What made that early warning possible, said Robert Derouin, deputy chief of meteorological operations at the National Weather Service's National Meteorological Center, is bigger computers, more raw data and a better understanding of how to put the two together to accurately mimic the daily clash of forces in the atmosphere.

Forecasters at the center, located in a run-down office building in Camp Springs, first spotted the brewing atmospheric imbroglio on Monday, March 8 -- four days in advance.

Day-by-day, the scientists watched the storm develop, just as their computers predicted. Meanwhile, they fed their increasingly gloomy weather maps and data to 274 local weather service offices scattered around the country, as well as private forecasters, television and radio stations.

By Tuesday, local forecasters began spreading the news that snow was expected over the weekend as far south as Georgia. By Wednesday, "we had the first indication that it was going to be a superfantastic East Coast storm," said Paul J. Kocin, a research meteorologist with the meteorological center.

Road crews and the National Guard were alerted. Motorists canceled weekend travel plans. Most folks had ample time to strip supermarket and video store shelves, then hunker down in their dens and club rooms for the long winter's weekend.

Fewer people were killed, chilled, stranded and stressed than if the storm had sneaked up unnoticed. The credit, colleagues say, belongs mostly to the meteorologists and computer jockeys at Camp Springs.

Eugene M. Rasmusson, a senior meteorologist at the University of Maryland at College Park, called it "a stunningly good forecast" that took some courage to make.

"I told my wife Friday evening, this storm's either going to be one tremendous hit or one tremendous bust," he said. "The weather service didn't hedge on it. They went all out. And it worked out beautifully."

In 1955, computers could calculate local weather patterns with reasonable accuracy for only about three days in advance. Today, local forecasts are relatively reliable out about six days.

Those three extra days may not seem like much, but predicting the weather is very difficult because of what scientists call the butterfly effect. The weather is so sensitively balanced, that it can be strongly influenced, in the long run, by tiny changes in conditions.

The beating of a butterflies wings in Brazil, it is sometimes said, can spawn a hurricane in the Caribbean three months later.

Of course, meteorologists hope the weather is not quite that sensitive.

But so far they have little luck with extremely long-term forecasts.

The weather service's detailed, local 24-hour forecasts are now more than 95 percent reliable.

By contrast, monthly forecasts -- which predict broad temperature and precipitation ranges for regions of the country -- are just 14 percent better than random guesswork for temperatures and 5.7 percent better for rain or snow.

Ninety-day forecasts score just 5 percent for temperatures and 3 percent for precipitation.

Predicting that the Blizzard of '93 would develop four days in advance was not an astounding feat in itself, meteorologists said.

The storm was a classic example of what is called a Northeaster -- where cold polar air sweeps south along the Mississippi Valley into the Gulf of Mexico, picks up prodigious moisture and then takes a U-turn up the East Coast, spreading snow in winter and rain in summer.

"This is just sort of a hybrid of a fairly typical weather system, just very extreme," said Mr. Kocin, an expert on Atlantic storms.

What was remarkable was that forecasters saw early on that the storm would do something very unusual -- quickly approach peak intensity over the Gulf and the southern United States. Typically a Northeaster doesn't turn vicious until it reaches New England.

Meteorologists were able to predict the storm's size, its production of rain and snow, its timing and its track with great precision, Dr. Rasmusson said.

"I started forecasting weather in 1952 when we drew our own maps with a pencil, so I've seen the changes," he said. "Even as recently as three years ago, I don't think this kind of accuracy would have been possible."

Every day, the Camp Springs scientists harvest thousands of readings of air temperature, pressure, wind speed and other data from all over North America, the Caribbean, North Atlantic ,, and the North Pacific.

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