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September-October 2011

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Retrospect: September 11, 2001: Attack on America

Caption: NOAA/NWS Daily Weather Map for 8:00 a.m. EDT, September 11, 2001. High pressure behind an advancing cold front dominated the eastern United States, providing a beautiful and pleasant start to a day that would end in tragedy with the worst terrorist attack on American soil.

“Tuesday, September 11, 2001, dawned temperate and nearly cloudless in the eastern United States.” This simple, unassuming statement serves as the opening line to the official 9/11 Commission report on the series of terrorist attacks that were launched against the United States that morning. The attacks, which killed approximately 3,000 people in New York City; Arlington, Virginia; and rural Pennsylvania, were carried out by the terrorist organization al-Qaeda, who hijacked four commercial airliners and used them as guided missiles, striking each of the Twin Towers of New York's World Trade Center and the Pentagon, with the fourth plane crashing in a field near Shanksville, Pennsylvania, before it could reach its apparent target.

The opening line to the commission's report underscores the role that weather played in people's lives at the time. Barely a week after the Labor Day holiday, many Americans across the eastern United States awoke to pleasant, late summer weather, not realizing that something much more profound and insidious than the seasons was about to change—and alter their lives, their country, and the world as they knew it forever.

Just two days prior to the attacks, an article titled “What's Doing in New York” appeared in the travel section of the Sunday edition of The New York Times, proclaiming that fall “is the city's most glorious season, with clear skies and a crackle in the air.” Unlike the “signature lineup of cool weather events” that The Times proclaimed “means visitors pour into town and residents stay put until the moment summer evaporates,” the clear skies of September 11 only gave way to a scene that one witness described as “hell on earth.”

“The day began in the brilliance of a late summer morning, then was obscured in gray balls of dust and smoke that seemed to touch everyone,” wrote The New York Times the next day.

A series of warmer-than-average 80-degree days was about to come to an end, as a cold front pushed across the eastern United States, bringing with it cooler, drier air and clear skies associated with a large area of high pressure centered over the southern Great Lakes.

Several hundred miles out in the Atlantic, Hurricane Erin—the first Atlantic hurricane of the 2001 season—was weakening as it began to turn toward the north-northeast, away from the East Coast. Though it posed no threat to land, Erin had been producing large swells along local beaches and was one of the main headlines early that morning. In fact, The New York Times weather report on September 11 included a special “Focus” write-up on what it called “Hurricane Day,” explaining how in “9 out of 10 years since 1886, at least one tropical storm or hurricane has raged in the Atlantic on Sept. 11.”

Back in New York, the city's official weather observing site in Central Park reported clear skies up until 8:51 a.m., just five minutes after the first plane, American Airlines Flight 11, crashed into the North Tower of the World Trade Center. Two of the three major New York-area airports—La Guardia and JFK—also reported clear skies in the early morning hours, with partly cloudy skies by the time the first plane struck. At Liberty International Airport in Newark, New Jersey, skies remained clear all morning.

Could the fact that is was such a clear morning have been a factor in the hijackers' decision to strike that day? It certainly aided them in navigating and finding their targets, as none of the hijackers was a professional pilot, though several had taken pilot training courses in the United States. “For those heading to an airport,” the 9/11 Commission report stated, “weather conditions could not have been better for a safe and pleasant journey.” The 8:51 a.m. temperature reading was 68°F at Central Park, 72°F at La Guardia, and 73°F at both JFK and Newark Airports.

When American Airlines Flight 11 struck the North Tower of the World Trade Center at 8:46 a.m. and United Airlines Flight 175 struck the South Tower at 9:03 a.m., the resulting explosions created a thick plume of smoke and debris that lasted for days. The 9:51 a.m. hourly METAR weather observation from La Guardia contained the coded message “FU PLUME SW DRFTG SE” in the remarks section, indicating that a smoke plume was observed to the southwest, drifting southeast. A special observation taken at 10:51 a.m. added additional detail to the statement with “FU AND DEBRIS PLUME SW FROM SFC-035 DRFTG SE,” indicating that a smoke and debris plume was observed to the southwest rising from the surface to a height of 3,500 feet and drifting southeast. Similar remarks would be included in observations from all three New York-area airports for the next two days, and at La Guardia and JFK well into the third day. Less than two hours after they were struck, “The mighty towers themselves were reduced to nothing,” The New York Times reported. “Dense plumes of smoke raced through the downtown avenues, coursing between the buildings, shaped like tornadoes on their sides.”

Less than an hour after the first plane struck the World Trade Center, the FAA ordered all civilian flights over United States airspace grounded—an unprecedented undertaking that was aided by the relatively fair weather that predominated across most of the country, that day.

In the days and weeks following the disaster, the monitoring of weather conditions played an important role in the recovery efforts with government, private sector, and academic researchers providing detailed forecasting and air quality support services at both Ground Zero in lower Manhattan and at the Pentagon outside Washington, D.C. (For more on this, see “In the Wake of September 11” in the September/October 2002 issue of Weatherwise.)

Many have postulated that America lost part of its innocence on September 11, 2001. If we have regained any of it over the course of the past decade, perhaps it comes in the form of once again being able to enjoy a pleasant, late summer morning without the worry of what may come.

Contributing Editor SEAN POTTER is a New York-based Certified Consulting Meteorologist (CCM), Certified Broadcast Meteorologist (CBM), and science writer with an interest in weather history.

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