Was That a Tornado in New York City?

While we pick the branches from our stoops and await official ruling from the National Weather Service and the city’s Office of Emergency Management on whether that really was a tornado that caused Thursday night’s storm damage, here’s an overview of the choices they’ll have to make:

1) Judging by the Doppler radar echos during the event, was there significant rotation of the storm system? Doppler radar has the unique advantage of being able to determine wind speeds towards and away from the radar. Experts should be able to determine if rotation occurred by using this data. For those interested, here’s the radar that was recorded during rush hour Thursday night. Since a tornado warning was issued, NWS forecasters obviously believed that this storm was capable of producing rotation and funnel clouds.

2) Looking at the damage path on the ground, does it appear that the damage was caused by a funnel cloud? Debris strewn in twisting or converging patterns, trees falling in opposite directions, and “projectile” impacts are all evidence of tornadoes. Evidence of straight-line winds (from a downburst or microburst) could be things like debris blown all in the same direction, divergent debris patterns or localized pockets of damage. For more, or to try some amateur detection, check out the National Weather Service Office in LaCrosse, Wis.’s post-storm damage survey guidelines. (Alas: No corn fields to give researchers clues in Forest Hills.)

Until we hear back from the meteorologists visiting the affected areas, we’ll just have to amuse ourselves with video from the event and its aftermath. Here’s a video taken from a rooftop in Park Slope.

http://blogs.wsj.com/metropolis/2010/09/17/tornado-in-queens-brooklyn-new-york-city-how-to-tell/