Tornado Warnings: The Map
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.
Weather Ready Nation: Counties Warned for Tornadoes by CWAs
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 Elusive Tornado Emergency Product
In light of this year’s extremely violent tornadoes and the reaction to them amongst the meteorological, emergency management, and social science communities, I’ve spent a lot of time thinking about the National Weather Service’s (NWS) practice of issuing tornado emergencies. For those who don’t know, this product is, in theory, designed to serve as a “more severe” tornado warning. Essentially a tornado emergency is nothing more than a regular tornado warning with a variant of the phrase, “This is a tornado emergency,” contained somewhere in the text. This phrase could be contained somewhere in the initial tornado warning or in a follow-up statement known as a severe weather statement.
Over the last few days I have been working on putting together a collection of all tornado emergencies ever issued. The first one was issued on 3 May 1999, as a severe weather statement, as the Bridge Creek F5 tornado threatened downtown Oklahoma City. Since then this product has been issued over 100 times with varying success. Much like the success of the tornado emergency product, I have had varying levels of success in tracking down all the products ever issued. So far I am fairly confident that I have collected all of the tornado emergency statements since 2005. Unfortunately I have run into a problem with tornado emergencies prior to 2005. The problem stems from the fact that the, “This is a tornado emergency,” tagline can be placed in one of several NWS text products. All initial tornado warning statements that contained this tagline are archived and I am fairly confident I’ve retrieved them all. However, obtaining severe weather statements prior to 2005 have proven elusive. (The exception to this is the severe weather statements from the Fort Worth, TX office on 28 March 2000 when a tornado emergency was issued for downtown Fort Worth, which I have found.) This is where you, the amazing people of the Internet, can help. If you are in possession of, or know of, a tornado emergency prior to 2005 that is not listed on my Tornado Emergency page, please contact me as soon as possible.
In the coming days and weeks I will be updating the Tornado Emergency page with a listing of all known tornado emergencies and eventually will provide links to all of the text products and the verification.
About Patrick
Patrick Marsh is a Ph.D. student at the University of Oklahoma's School of Meteorology. He earned a Bachelors of Science in Mathematics and Physics (cum laude) from the University of Arkansas in 2005 and a Masters of Science in Meteorology in 2007. In addition to working on his doctorate, Patrick serves as the National Severe Storms Laboratory Liaison to the Hazardous Weather Testbed where his research interests lie in working with operational forecasters, data mining, data visualization, and all things high-impact weather. For more about Patrick's work, check out his complete CV!
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