2011 was a bad year for tornadoes, and 2012 has started with some dangerous ones as well. I’ve been wanting to visualize them for a long time and finally found a source of clean data – the Tornado History Project which allows you to download data that was cleaned from the Storm Prediction Center. There is some really interesting information in there:
- Time of day peaks and lows for tornadoes
- Most dangerous time of day (there are fewer storms at night, but they are just as dangerous)
- Southern states have a completely different set of peak months than the ‘tornado alley’ states
- The sheer number of tornadoes per year and on aggregate
- The increase in number of tornadoes recorded (lots of smaller ones are now recorded that were never before)
It also makes you think about population growth as state and once-rural population increases and how deadly encounters with tornadoes are likely to increase. Equally, how the advent of better weather radar and emergency warning systems can help save lives (excluding 2011, for tornadoes 4 or more on the Fujita – deaths have dropped from between 5 and 10 per storm to 1 to 2). Finally, there are some interesting questions around data quality, especially with historical data. The Fujita scale was only created in 1970 and changed again in 2007, so this brings into question equivalent comparison between the years. Also as the scale is somewhat subjective, based on damage to houses and crops, the data will be affected as our ability to measure damage has improved, but also as the increased likelihood that obvious damage to structures occurs (as there are more structures). And of course, there’s the fact that today we are much more likely to observe weak tornadoes than 50 years ago. Click here to go the viz.Creation notes: This is the first time I’ve used the path shelf in Tableau; in this case to draw the trail of the tornado – there are only touchdown and lift-off coordinates so all of the tracks are a straight line. I used some custom SQL to create the path information and to join a table containing state population and sq miles. I also have a desktop copy of the viz that has animation on the page shelf.