Weather Ready Nation: Counties Warned for Tornadoes by CWAs

Posted by on 14 Dec 2011 | 1 comment

UPDATE: Zac Flamig, a fellow graduate student at OU and founder of Weather Wary (iOS weather software development company), has turned these maps into an animation viewable on YouTube. Check it out!

In the wake of last night’s post, several questions were raised regarding the time periods of the two images. The biggest concern was that you can’t compare a 22-year average and a 3-year average, as the 3-year average is more easily biased by one or two high years than the 22-year average. Tonight I’ve added a plot that shows the number of counties under a tornado warning by National Weather Service County Warning Areas (CWAs) broken down by year.

Starting with 1986 and advancing toward 2010, one can easily see that the number of counties warned by CWA has increased substantially, with most of the increase occurring in last few years. Although this isn’t the same as the number of tornado warnings (because a single tornado warning could affect multiple counties), it is still an important number. This is because it represents the number of times NOAA Weather Radios would have sounded in each CWA. Why is that? This is because the NOAA Weather Radios, as they currently stand, cannot activate based on the storm-based warning. They are activated based on the county-level warning. Thus, two small storm-based warnings issued for the same county would require two activations of the NOAA Weather Radio for that county, even if the warnings were issued only minutes apart. Thus, for a large portion of the population, the county-level warning is what they would receive.

Tomorrow I’ll post similar maps but instead of counting the number of counties warned, I’ll count the number of tornado warnings.

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

Counties Warned (1986)

Counties Warned (1986)
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  • Jeff Duda

    Quoting you in this post: “This is because the NOAA Weather Radios, as they currently stand, cannot activate based on the storm-based warning. They are activated based on the county-level warning.”

    BINGO. This is part of the whole high-FAR-causing-lack-of-action issue. The NWS needs to revamp the warning technology.