Biases in the Severe Weather Report Database across Vermont and Northern New York

Severe weather records for Weather Forecast Office National Weather Service Burlington, Vermont, (BTV) date back to the 1950s. These records include reports of tornadoes, hail and convective wind gusts (measured and estimated). Spatial and temporal trends in severe weather occurrences across northern New York and Vermont were analyzed from 1950–2016 for the warm season convective months, May–September. All storm reports were accessed through the Storm Prediction Center Severe Weather database and plotted graphically using Excel and spatially with ArcMap GIS. For this study, the total number of reports from this database included 2379 wind reports, 953 hail reports and 59 tornado reports.

Overall, severe weather reports across Vermont and northern New York exhibit some of the same biases inherent within the national severe weather database. The annual distribution of wind and hail reports showed a sharp increase in reports following 1985. This is likely attributed to the implementation of a national warning verification program in the 1980s. Spatial plots of reports also show biases attributed to population, which are especially evident in hail and wind reporting, while tornado reports did not exhibit either one of these biases. Previous literature has shown that deployment of NEXRAD radars can augment reports due to increased detection of storms and subsequent issued warnings. However, annual differences in prevailing weather patterns that produce severe weather in New England can influence the ability to identify such artifacts. Additionally, the topography of the region, such as the low-lying plains of the St. Lawrence and Champlain valleys, and the high terrain of the Adirondack and Green Mountains, influence the spatial distribution of severe weather reporting. These topographic features not only influence the distribution of population, but also the locations of convective initiation and development of mesoscale boundaries. This was most noticeable in tornado reports which were more commonly seen in the St. Lawrence and Champlain valleys compared to the high terrain.