May 5, 2008
Residents in some rural Texas counties with a small population are less likely to be issued a severe thunderstorm warning by the National Weather Service than if they live in an urban county with a large population, even though the storm's intensity might be the same. That's just one of the findings from a Baylor University's 2008 study looking at the issuance of severe weather reports and severe thunderstorm warnings over a 20-year period.
The study analyzed choropleth maps and statistical data for 132 counties in Texas along the Interstate 35 corridor, and approximately 240 miles to the west of I-35 and 220 miles to the east. The study area, encompassing more than 122,000 square miles, is served by five National Weather Service Warning Forecast Offices - Fort Worth, New Braunfels (Austin/San Antonio), San Angelo, and out-of-state offices in Shreveport, La., and Norman, Okla.
The Baylor study found:
Nearly twice as many severe thunderstorm warnings were issued for the urban, more-populated counties compared to the rural counties, and more than four times the number of severe weather reports like large hail or damaging wind were issued for urban counties.
Not only are there fewer warnings issued in distant rural counties, but severe thunderstorm warning false-positive rates also are higher for the rural counties in the study area. False-positives, or unverified warnings, are severe thunderstorm warnings that are issued where no documented severe thunderstorm event occurred during the time the warning was in effect.
The physical distance between the storm and the warning center also played a role. Specifically, when researchers compared the normalized average number of severe thunderstorm warnings to the distance to the Fort Worth NWS office, there was an overall decrease in the number of severe thunderstorm warnings when the distance from the Fort Worth office was increased. Researchers found the outermost counties received about half as many warnings as Dallas and Tarrant counties.
Additional non-meteorological county warning and severe weather report biases were found for several particular counties in the study area that may relate to socioeconomic factors and physiographic influences. The proximity to interstate highways also appears to have an effect on the reporting of severe weather events and the issuance of severe thunderstorm warnings.
"Ideally you would want some sort of uniform standard that mirrors the meteorological truth," said Kevin Barrett, a geology graduate student at Baylor who conducted the study. "It seems logical to assume that meteorologists, in general, are concerned about the greater good of the population, and that more of a 'heads up' would be given to larger cities than rural areas. But, acting on a purely scientific basis, the weather person issuing the severe weather warning should issue it based on the strength of the storm, without regard for the population density of a certain area."
Severe thunderstorm warnings are issued based on radar returns, surface weather instrument reports or visual observation by storm spotters or pilots, although more of an emphasis is put on visual observation than radar data, Barrett said.
The results were presented at the Association of American Geographers conference in Boston.
For more information, contact Kevin Barrett or Dr. Don Greene at (254) 710-2361.
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