When tornados strike, which way do they travel?

These gorgeous maps have the answer. Created by datavisualization expert John Nelson, these "Tornado Travel Maps" depict the relative proportion of more than 60 years of U.S. tornadoes by their direction of travel. Notice a pattern?

The maps are the latest in Nelson's growing ouvre of gorgeous, natural-disaster-themed cartography. To date, he's produced maps depicting more than a century's worth of global earthquakes, over 150 years of tropical storms and hurricanes, and a slew of major U.S. wildfires. Each map is created from data made publicly available by organizations like NASA, NOAA and the USGS. Every one of them is stunning, combining troves of data with arresting visualizations to great (and incredibly informational) effect. Nelson's latest creation is no exception. What's more, it might one day be used to improve emergency response protocols for some of America's most devastating tornados.

He writes:

The data comes from archived tornado data via the NOAA/NWS Storm Prediction Center. Not surprisingly, the lion's share of storms travel in a northeastern direction along with the prevailing winds (and carry F5 storms at double the rate as the other quadrants). I was interested in seeing just how great a proportion actually do. Beyond that, I was interested in seeing regional trends where historic storms have bucked that NE trend and traveled some other direction. [Emphasis added.]

When tornados strike, which way do they travel?

Above: historic proportion of tornados by bearing, weighted by distance and intensity | via John Nelson

Nelson tells io9 that these maps are part of a larger, ongoing project to divide the country into tornado warning zones that incorporate the "general runway of storm movement."

The idea came from Robert Staskowski, a meteorologist in New York, who contacted Nelson in the aftermath of last month's devastating storms in Oklahoma. According to Staskowski, the tornado warning grid would build upon existing maps utilized by the National Weather Service (NWS).

In an email to io9, Staskowski says that the NWS, in combination with local weather services and news outlets, does an admirable job at getting warning information to the public in a timely manner, but he thinks steps could be taken to improve the system:

When tornados strike, which way do they travel?

Above: Screenshot of a weather watch issued on Monday, June 17th.

Currently the National Weather Service creates a Tornado Watch box [aka "weather watches"] when conditions are favorable for a tornado or they issue a Tornado Warning when a tornado has been confirmed by radar or spotters. These warnings usually cover a county or two within a state and are giving a cone designation similar to that of a hurricane to indicate which direction the tornado is likely to go. But I truly feel more can be done to save lives.

Staskowski envisions a map that incorporates the predominant angle of travel of the most powerful tornados, and describes how it might be put to use (for a more detailed account of the system, see this helpful visual explanation created by Staskowski):

Lets say you overlay a grid over the midsection of the country from lets say Colorado to Pennsylvania using angles of 47 degrees. Then divide from South to North the grid into 2 mile sections starting at Tornado Zone 1 in Florida to Tornado Zone 400 crossing thru Pennsylvania.

[Let's use the 2013 Moore Tornado] as an example. From what I understand the tornado moved from the Newcastle area into Moore and the path of this tornado appears to be at an angle of 47 degrees give or take a degree or two. Now lets say hypothetically this tornado formed in Tornado Zone 150. Now everyone who lives in Tornado Zone 150 would know they live in this zone because they own a map which was distributed by their local governments. Now let's say [a meteorologist] is reporting on this live. Typically he would say the storm is in the vicinity of Newcastle moving towards Moore which to me could provide some confusion to people who may be in a panic and not know what direction the storm is coming from or going to or what direction to head to get out of harms way.

Now imagine [the meteorologist] makes the following broadcast. "A tornado has formed in Zone 150 in the Newcastle area and is expected to affect Zones 149 thru 151. People living in Zone 150 in the vicinity of Moore should evacuate immediately heading South and East towards Zone 148 and should seek shelter immediately in Zones 148 and below. The tornado which is currently in Newcastle will reach Moore in approximately 30 minutes." Of course you don't want people in Newcastle leaving their houses and jumping in their cars to head South but the people in Moore would have a much better idea of what direction to head in to be safe and avoid the path of the tornado.

Staskowski admits such a grid system has a "very long way to go before it can ever be tested in a real life situation," but his ideas – in combination with Nelson's visualization work – raise important questions about how we can use past data to better respond to threats posed by natural disasters.

Whether the travel trends of America's most powerful storms are consistent enough for us to design better emergency response procedures remains to be seen. But if anyone is up to the challenge of visualizing that threat, it's Nelson. We look forward to seeing what he and Staskowski can produce.

For more information, analysis, and a technical overview of the map's creation, visit John Nelson's blog. For more on the proposed tornado warning grid system, see this helpful visual explanation prepared by Staskowski.