Adam Pearce

Twister activity gets intriguing treatment in this explorable visualization.

Now that the American tornado season is petering out – petering but not over, as twisters can strike in any month – it's worth looking at what kind of year the country had in terms of big spinning dreidels of destruction.

The good news it that the total number of tornadoes appears like it will be far lower compared to previous years. At the end of August there were 710 verified touchdowns, according to NOAA's Storm Prediction Center. Preliminary stats for September and October add roughly 50 more. With only two months of 2013 left to go it's unlikely the twister count will get near that of past years: 939 in 2012, 1,691 in terrible 2011, and 1,282 in 2010.

Still, at least 45 individuals died by NOAA's count, mostly during the spring inside the screaming wind corral known as Tornado Alley. The worst disaster in terms of mortality was when an EF-5 brute tore through Moore, Oklahoma, and its surroundings on May 20, blasting apart two-dozen structures, killing 24 people, and leaving about $2 billion in damages. For those who don't remember what an awful thing that was, this chaser footage might shake loose memories:

There's a slight chance November could ratchet up the tornado activity, as meteorologist Greg Forbes explained a while ago on the Weather Channel. "November is thought to be second season," he said. "Not so much in that it has a huge jump in the number of tornadoes, but the few days they do occur there can be tornado outbreaks with a large number of tornadoes and some strong tornadoes." If that does occur, you can expect to see a slight bit more angry red scribbling on the above map, which shows every recorded tornado to maraud across the states from 1950 to 2012.

The interactive visualization, available here for your geeking-out pleasure, was assembled by New York City technoartist Adam Pearce, who also did that wonderful presentation of 500 years of meteor spottings. Inspired by a similar model made by John Nelson, Pearce whipped up a map that gives the track and wind intensity for each of the twisters. While meteorologists have noted more than 21,000 tornadoes in the past 63 years, only long-lasting ones that traveled for more than 20 miles are shown here (just under 2,000). Fatter lines represent more powerful ones, and the tracks are approximate, as NOAA "only collects start and end locations – tornadoes do not actually travel in perfectly straight lines," explains Pearce.

He gives more details via email:

Tornadoes with a lower F-Scale are bluer and slightly transparent. To draw more attention to tornadoes with a higher F-Scale – those with the highest wind speeds and which did the most damage – they are drawn in a solid red. Another aspect of the map that I'm happy with: If you're patient with the sliders and drag a small selection across the F-Scale histogram, the color scheme is self-documenting.

In a neat twist, you can adjust the wind direction to reveal the weird twisters that traveled in uncharacteristic southern or northwestern directions. There are also options to search by the hour of the day: Around 5 p.m. seems to be the witching hour for these weather ghouls. Click on a state to get a close-up picture of its historical twister activity, as shown in this short video:

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