Tornado Warnings: The Map

Posted by on 21 Dec 2011 | 6 comments

One of the most frequently asked maps is for all plot of all the tornado warnings. Here are the tornado warnings issued by year. Each warning was color-filled red with an alpha value of 0.1. Thus, it would take 10 overlaps for the color to display as true red. Thus, the colors are shaded from light pink (no overlaps) to red (at least 10 overlaps). 1 October 2007 the tornado warnings transitioned from county-based warnings to storm-based warnings.

As you can see, the number of warnings increased up through the start of storm-based warnings. After that time period, the number of warnings increased, but the overlap has decreased. One thing that is very apparent is that the number of warnings across the southeast United States has certainly been on the increase…

Also, one visual aspect that should be more disturbing that it is, notice the number of county borders that stand-out in the storm-based warning maps of 2008-2010.

The images begin with 1986 in the upper-left and increase from right-to-left ending with 2010 in the bottom-right.

All Tornado Warnings (1986)

All Tornado Warnings (1986)
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  • Brad Barrett

    Very nice images- I’d love to do some climotology studies using these data – perhaps re-examine the relationship to the various climate indices – the results could be very interesting :)

  • Greg Stumpf

    Pre-2008, I know that the WarnGen software always had the storm-based polygon capability from the get-go, but were the lat-lon pairs just not recorded anywhere? –greg

  • http://www.patricktmarsh.com pmarshwx

    Definitely, Brad! I’m hoping to go that route myself. It’s just tough to do when this has nothing to do with my dissertation and is “just for fun”! I’m trying to code up some efficient gridding routines to put all the warnings on a 1KM grid. Conceptually I’m almost there, then have to code it up…

  • http://www.patricktmarsh.com pmarshwx

    Greg, I have the polygons (if they were issued) from 2002 onward. However, I plotted only the official warnings here, which meant using county-based until 1 October 2007.

  • Anonymous

    Do you know where to find documentation on the switch?  I compared the files and it looked like for a little while they produced BOTH county and polygon warnings.

  • http://www.patricktmarsh.com pmarshwx

    Zack, the files contain a field that has a P (Polygon) or C (County) so that you can differentiate between the two.  The switch was made on 1 October 2007, but a lot of the warnings before then contained polygons. Any county touched by the polygon was subsequently warned.