September 11, 2012 weather map (National Weather Service)

Meteorologist Sean Potter, writing for Weatherwise magazine, opens his retrospective on the weather of 9/11/2001 like this:

“Tuesday, September 11, 2001, dawned temperate and nearly cloudless in the eastern United States.”

The still, clear weather enabled the hijacked flights to take-off and may have assisted the terrorists in carrying out their plots. As Potter explains:

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.

September 11, 2001 weather map (National Weather Service)

Both today and in 2001, the picture perfect late summer (or early fall) weather resulted from sprawling areas of high pressure.

Today’s conditions are slightly cooler compared to 2001 in the East for two reasons: 1) The high pressure area is stronger than its 2001 counterpart. 2) It’s centered smack dab over the East Coast today whereas it was focused on the Ohio Valley in 2001.

Morning lows ranged from mid-50s to mid-60s (between the cooler suburbs and urban areas) in 2001 in both the New York City and Washington, D.C. regions. Today’s lows ranged from the more crisp upper 40s to upper 50s.

Under full sunshine, high temperatures promise to be very similar today compared to the low 80s of 2001, maxing out in the upper 70s.

It’s interesting to note that in both years, there were active tropical systems in the mid-to-high latitudes near or just off the East Coast of North America. In 2001, after a close brush with Bermuda, hurricane Erin spun several hundred miles east of New England.

Hurricane Erin, September 11, 2001. The inset panel on the upper right shows smoke from the Twin Towers as viewed by the GOES-8 satellite. (NOAA)

Smoke from the Twin Towers. Via NASA “This true-color image was taken by the Enhanced Thematic Mapper Plus (ETM+) aboard the Landsat 7 satellite on September 12, 2001, at roughly 11:30 a.m. Eastern Daylight Savings Time.” (NASA Earth Observatory)

Today, tropical storm Leslie is lashing Newfoundland - having followed a similar track to Erin.

Satellite view of hurricane Leslie on September 10. Today it is a few hundreds miles north of that position having made landfall in Newfoundland. (NOAA)

Mercifully, the skies are smoke-free.