By Michael E. Ruane
Washington Post Staff Writer
Saturday, February 11, 2006; B01
There was no doubt the snow was coming. Meteorologist Steve Rogowski, watching the weather system unfurl on three big computer screens, predicted four to eight inches. The question for the forecasters at the local National Weather Service office yesterday was: How much more to tell you?
David Manning, the warning coordination meteorologist, suggested adding the words "blowing and drifting snow" to the forecast. But Meteorologist-in-Charge James E. Lee warned that could be too much data. Plus, coastal storms produce moist snow that doesn't blow. And the storm they had been tracking all day was 12 hours and 1,000 miles away.
Better to be succinct, Lee said: "Heavy Snow Warning."
That seemed to sum things up yesterday as the year's first significant winter storm drifted across the South and veered up the Atlantic Coast, threatening the Washington area with up to 10 inches of snow today and tonight and New York and New England with blizzard conditions.
The snow, perhaps mixed with sleet, was forecast to begin early this morning in some areas. It was expected to intensify this afternoon and evening, then taper off overnight, the weather service said.
More snow would fall east of the District -- in Southern Maryland and eastern Virginia -- with areas west of town getting less, the weather service said.
The storm, accompanied by low temperatures, marks a return to the full spectrum of winter. The government said last month was the nation's warmest January on record.
Aided by a northern flow of the jet stream, last month's average temperature was 39.5 degrees -- 8.5 degrees above the mean, according to the National Oceanic and Atmospheric Administration (NOAA).
But the jet stream brought back the cold, and the Gulf of Mexico and the Atlantic Ocean provided moisture, prompting the Washington region to lurch yesterday into storm preparation mode. Snowplows and shovels were readied, and Metro canceled track work scheduled for today and tomorrow.
At the weather service's Baltimore-Washington field office, in Sterling, a team of meteorologists worked to sift and weigh an avalanche of computer modeling data and put it into plain forecast language.
Much of the work involved comparing the output of three huge computers, nicknamed Red, White and Blue, that use mathematical models to process weather data and generate forecasts, a NOAA spokesman said.
But the models don't always agree, and the forecasters, often under intense pressure, must reach conclusions based on conflicting data. "The models vary from system to system," Lee said, "and that's part of what we do here, is analyze which model is going to work best for each particular situation."
Lee said his meteorologists know each model's strengths and weaknesses. "If it was a perfect system, there probably wouldn't be much of a need for forecasters," he said. "But it's not. Limitations remain. And that's where our forecasters come in."
As Lee sat before a bank of computer screens depicting versions of the coming storm, he showed how the model forecasts could diverge.
One, the Global Forecast System, or GFS, predicted maximum local accumulations of about 10 inches. But another, the North American Mesoscale model, or NAM, forecast maximum accumulations of about four inches.
"We're in a nice position when the models come together in what we call a coincident solution," Lee said. "Those are our best days.
"This," he said, "is a nice challenge for us."
Rogowski, who was in the forecasting hot seat yesterday afternoon, said he was analyzing four or five model forecasts as well as other data.
Lee said today's storm is the result of two systems -- one from the gulf, the other from the upper Midwest -- that merged overnight in southern Mississippi. The system's center was expected to be over South Carolina by midday today and over North Carolina's Outer Banks by tonight.
Lee said it was expected to slide north off the New Jersey coast early tomorrow and "bomb out" -- rapidly intensify -- as it rumbled across New England. Accumulations of a foot or more of snow were forecast there. "Looks like the jackpot could be up in southern New England come Sunday," Lee said.
Tomorrow's forecast in the Washington area was for cloudy and cold conditions with a chance of light morning snow.
