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.
Corrections to Previous Posts
It is with regret I am forced to announce corrections to two previous posts:
Weather Ready Nation: Counties Warned for Tornadoes By CWAs
and
Weather Ready Nation: Tornado Warnings By CWAs.
For the post, Weather Ready Nation: Counties Warned for Tornadoes By CWAs, the only update has been to color white all CWA areas with 0 counties warned for tornadoes. Previously these CWAs were colored cyan making it impossible to differentiate between WFOs that warned no county for a tornado and WFOs that did warn counties for tornadoes.
For the post, Weather Ready Nation: Tornado Warnings By CWAs, the updates were a little more serious. I first applied the previous correction so that CWAs with no tornado warnings would be colored white. After doing this correction, I noticed that some of the newer CWAs were consistently white in the early years. I realized this was because the tornado warnings had been issued by different WFOs, some of which no longer exist. To correct for this, I took the county UGC (Universal Geographic Code) of each tornado warning and converted it to the FIPS code. I then took the FIPS code and converted that to one of the current (2011) WFOs. Thus, the maps now depict the number of tornado warnings issued for each geographic region, marked by the current CWA boundaries.
As is always the case, I strive to keep my posts factual and will post corrections as soon as errors are brought to my attention.
Caption This: Me at the Weather Ready Nation Conversation
Those who know me well know that I absolutely love to tease those with whom I am friends. To this end, below is a rather unflattering picture of me taken this week at the Weather Ready Workshop. I encourage everyone to take a moment and create a caption for this photograph. Please post your caption in the comments! (And, please, try and keep the captions somewhat clean!)
Weather Ready Nation: Tornado Warnings by CWAs
Tonight’s blog post depicts the number of tornado warnings issued by year by CWA. I should add a disclaimer: I am using the current CWA boundaries for all prior years. Thus, it one runs the risk of making incorrect assessments if one directly compares the specific increase in CWA tornado warnings counts. Instead, the idea is to look at the general trend in the number of warnings issued by forecast offices.
Data for 2007 and later years need to be understood in the context that WFOs have switched from county-based warnings to storm-based warnings. Thus, it is possible to have situations where multiple storm-based warnings are in effect when in the past a single county-based warning would have been issued. The flip side to that is, a single storm-based polygon can now capture 2 or more counties, which would have required multiple county-based warnings in the old system.
As I mentioned last night, the number of warnings issued can be thought of as a cumulative measure of the number of times the NOAA Weather Radios would have sounded in a specific CWA. Thus, the increasing number of warnings issued can be thought of in terms of the National Weather Service requesting more responses from the residents in their CWAs.
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.
Weather Ready Nation: Tornado Warning Frequency
Today kicked off the first day of the Weather Ready Nation: A Vital Conversation. (OU is recording and posting the presentations on the web.) Dr. Harold Brooks of the National Severe Storms Laboratory really got things going with a presentation on our known challenges. One of his main take-away points was that the number of tornado warnings issued has dramatically increased in the recent era. To illustrate this point, I provided two county-level heat maps (below). The top figure is the average number of tornado warnings per county per year from 1986-2007. The bottom figure is the same figure except for 2008-2010. As you can see, the average number of tornado warnings per county per year has increased almost uniformly across the county, although the increase is much larger in some areas and almost non-existent in others. Whether or not this is an improvement in National Weather Service “service” is one of the topics open for discussion in the following days.
I’m sure I’ll create more figures in the coming days.
Tornado Emergencies: The Map
Below is a map of all tornado emergencies issued since 1999. Keeping with my definition of a tornado emergency, the polygons plotted are the polygon described by the “LAT…LON” tag at the bottom of either a) the first severe weather statement (SVS) that contained the “Tornado Emergency” phrase, or, if no “LAT…LON” tag was present in the SVS, b) the parent tornado warning (TOR). If the “LAT…LON” tag was not present in either the SVS or the TOR, I used the county listed in the original TOR. This only happens 3 times: Ochiltree County, TX (2000); Johnson and Marion County, IN (2002); and Hancock County, IN (2002).
I’ve done more analysis, but will save that for later.
And, since I know I’ll be asked, here is the same map but without 2011.
About Patrick
Patrick Marsh is a Ph.D. candidate 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 from the University of Oklahoma 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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