Archive for July 2008

The SPC Archive and the Tornado History Project

One of my favorite recently added features of the site (see Major Upgrade to Tornado History Project 7/19/08) is the ability to easily correlate each tornado in the Tornado History Project database to the original line (or lines) in the Storm Prediction Center (SPC) archive. Why is this important? It is not uncommon for users to email me with a comment such as:

The county listed for tornado X is wrong. It should be Y – I know because it hit my house. Why don’t you do a little research before putting this on the internet?.

Yikes! While I want to know when there is a suspected error in the data, I also want to be clear where the information comes from. So, this will make it much easier to tell if the Tornado History Project is accurately reporting the data as given in the original SPC archive. In short, it adds transparency to the site and takes the mystery out of where the data comes from. And in cases where the Tornado History Project has changed any of the data (which is very rare), notice is given.

Let’s take a look at where you can find this info. On any individual tornado map page, all stats for that tornado are shown in an easy to read format immediately under the map as shown in the picture below. The last line of the section shows the actual text from the SPC archive used to generate those stats.

Of course, being able to actually see the original line from the SPC archive isn’t quite enough. It is also important to know how to read and interpret the information. So, a link is also given to the SPC instructions that explains what each piece of information actually means.

I should point out that there is one situation in which the approximate path shown for a specific tornado may not actually be based on the data in the SPC archive. Please see a previous blog entry (Enhanced Paths Explained 7/19/08) for more information.

And finally, there is one more note on this…Users must be logged in to see the corresponding line (or lines) from the SPC archive, so if you don’t see anything it, just login or register for a free account and you’ll be all set.

Enhanced Paths Explained

One of the most exciting new features of the site (see Major Upgrade to Tornado History Project – 7/19/2008) is the inclusion of enhanced path data derived from the National Climatic Data Center (NCDC) historical archive (thanks to Stuart Hinson for providing access to the archive!) While there are many differences between the Storm Prediction Center (SPC) historical archive (the primary source for the site) and the NCDC archive, the most significant difference is the method used to give coordinates.

In a nutshell, for tornadoes in which path data is available, the NCDC archive gives latitude and longitude coordinates when a tornado enters another county, while the SPC archive only gives coordinates when a tornado enters another state. This means that multi-county tornadoes in the NCDC database may have more data points available to draw a more detailed approximate path on the map. Thus, instead of the straight lines generated for SPC derived paths, NCDC derived paths generally have more turns and zig-zags.

How big of a difference does the inclusion of NCDC data make? Well, that depends on the number of NCDC derived data points given for any specific tornado, but let’s look at an example. The screenshot below shows a few F5 tornado paths using SPC data. As you can see, the approximate paths are straight lines, except for where a tornado crosses a state line.

The screenshot below shows the same area using NCDC derived data, when available. As you can see, some of the paths show a greater amount of detail.  Compare the apparent path near Jackson, Mississippi, for example.  With the enhanced path data below, the path passes the city from the South rather than the North.  And the more you zoom in, the more the difference will become apparent.

Displaying enhanced path data was not an easy task and took me almost a year to complete. The main issue was that there was no easy way to match up the tornado records between the two historical archives. I had to do quite a bit of manual tweaking to get it to work. Nevertheless, I think it was well worth the effort. I haven’t done an exact count, but I estimate that there are roughly 2,000-3000 tornadoes with enhanced path data, out of the 50,000 tornadoes in the database (the vast majority of tornado paths are short and only affect a single county.) Please note that you can only see enhanced path data when you are logged in.

I believe this to be the first time anything like this has been done. If someone knows different, please let me know. In any case, I hope you will sign up and do your own tornado search.

Major Upgrade to Tornado History Project

It has been a long time coming and is long overdue, but I have finally released a significant update to the Tornado History Project. For those who have been here before, the first thing you might notice is a change to the general look of the site. In short, it just looks better. But that is minor compared to the new features. I’ll post more in-depth details on some of the new features later, but the major ones include:

  • Historical data extended through 2007
  • A user account system
  • Enhanced tornado path data for select tornadoes (see Enhanced Paths Explained 7/19/2008)
  • Ability to correlate any tornado with the related line in the original SPC archive
  • Ability to export custom data searches
  • New buttons on the map, including experimental integration with Google Earth
  • Improved functionality in the tornado forums (there are over 50,000 forums available.) Improvements include:
    • Immediate posting of user comments (no need to wait for them to be approved)
    • Ability to watch any tornado forum for comments
    • A user ranking system (F0 through F5)
  • Other minor improvements

While these improvements are important, their real value is that they are the necessary foundation for future development. Keep checking back as I hope to improve the site even further. And remember, the purpose of this site is to recreate the history of as many tornadoes as possible through eyewitness accounts, personal memories, photos, and videos. I can’t do that alone – I need your help. So, tell your friends about this site, post your own memories or photos and videos, and, if you can, make a small donation.