The Spatial Distribution of Contiguous United States Thunderstorm Related Short-Fuse Severe Weather Warnings
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The purpose of this research is to define the spatial distribution of short-fuse severe weather warnings as they relate to population density within the Contiguous United States (CONUS). Using Geographic Information Science and statistical techniques, the overall spatial pattern of National Weather Service (NWS) warning issuance was determined along with correlations to population distribution. Four basic short-fuse warning types were studied; severe thunderstorm county-based warnings, severe thunderstorm storm (polygon) based warnings, tornado county-based warnings, and tornado storm-based warnings. Severe weather warning and ambient population data were obtained from United States Government sources and were spatially joined to the United States Geological Survey’s 7.5 minute, 1:24,000 (1:25,000 metric) Quadrangle Series. Counts of the number of warnings issued and population density for each Quadrangle in the CONUS were statistically compared to find correlations between the two data types. The direction of the center of mean warning distribution was compared to the geographic center of National Weather Service County Warning Areas to determine if a directional bias exists. This study finds that a spatial relationship to population exists for three warnings types: severe thunderstorm storm-based warnings, tornado county-based warnings and tornado storm-based warnings. Population bias statistical evidence is most prevalent for severe storm-based warnings. This study also finds that the spatial distribution of warnings has shifted with the transition to storm-based warnings from the central part of the Nation to the southeastern United States. The annual frequency of county-based severe and tornado warnings was highest for the Central Plains, where severe storm-based warnings were issued for distinctly defined county warning areas mainly in the south and southeastern United States. Tornado storm-based warnings were issued more frequently in the Deep South, southeast, and Gulf Coast areas. Several National Weather Service Weather Forecast Offices showed a tendency to have a high frequency of warnings when compared to neighboring NWS offices. Directional distribution varied drastically between weather forecast offices, but the overall tendency was for warnings to be issued to the south of the geographic center of National Weather Service County Warning Areas. Several weather forecast offices showed a tendency to issue more warnings in the up-range direction associated with climatological storm movement. Results from this study indicated that human influence is the main factor that contributes to warning frequency and spatial distribution.