Geological and Atmospheric Sciences Publications Geological and Atmospheric Sciences 2010 Spring and Summer Midwestern Severe Weather Reports in Supercells Compared to Other Morphologies Jeffrey Dean Duda Iowa State University, [email protected] William A. Gallus Jr. Iowa State University, [email protected] Follow this and additional works at: http://lib.dr.iastate.edu/ge_at_pubs Part of the Atmospheric Sciences Commons, and the Geology Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ ge_at_pubs/61. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Geological and Atmospheric Sciences at Iowa State University Digital Repository. It has been accepted for inclusion in Geological and Atmospheric Sciences Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Spring and Summer Midwestern Severe Weather Reports in Supercells Compared to Other Morphologies Abstract This study compares severe weather reports associated with the nine convective system morphologies used in a recent study by Gallus et al. to an additional morphology, supercell storms. As in that previous study, all convective systems occurring in a 10-state region covering parts of the Midwestern United States and central plains were classified according to their dominant morphology, and severe weather reports associated with each morphology were then analyzed. Unlike the previous study, which examined systems from 2002, the time period over which the climatology was performed was shifted to 2007 to allow access to radar algorithm information needed to classify a storm as a supercell. Archived radar imagery was used to classify systems as nonlinear convective events, isolated cells, clusters of cells, broken lines of cells, squall lines with no stratiform precipitation, trailing stratiform precipitation, parallel stratiform precipitation, and leading stratiform precipitation, and bow echoes. In addition, the three cellular classifications were subdivided to allow an analysis of severe weather reports for events in which supercells were present and those in which they were not. As in the earlier study, all morphologies were found to pose some risk of severe weather, and differences in the two datasets were generally small. The 2007 climatology confirmed the theory that supercellular systems produce severe weather more frequently than other morphologies, and also produce more intense severe weather. Supercell systems were especially prolific producers of tornadoes and hail relative to all other morphologies, but also produced severe wind and flooding much more often than nonsupercell cellular morphologies. These results suggest that it is important to differentiate between cellular morphologies containing rotation and those that do not when associating severe weather reports with convective morphology. Keywords bow echoes, cellular morphology, convective events, convective systems, data sets, isolated cells, radar imagery, severe weather, squall lines, stratiform precipitation, super cell, radar, storms, weather forecasting Disciplines Atmospheric Sciences | Geology Comments This article is from Weather and Forecasting 25 (2010): 190, doi: 10.1175/2009WAF2222338.1. Posted with permission. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ge_at_pubs/61 190 WEATHER AND FORECASTING VOLUME 25 Spring and Summer Midwestern Severe Weather Reports in Supercells Compared to Other Morphologies JEFFREY D. DUDA AND WILLIAM A. GALLUS JR. Department of Geological and Atmospheric Science, Iowa State University, Ames, Iowa (Manuscript received 23 July 2009, in final form 18 September 2009) ABSTRACT This study compares severe weather reports associated with the nine convective system morphologies used in a recent study by Gallus et al. to an additional morphology, supercell storms. As in that previous study, all convective systems occurring in a 10-state region covering parts of the Midwestern United States and central plains were classified according to their dominant morphology, and severe weather reports associated with each morphology were then analyzed. Unlike the previous study, which examined systems from 2002, the time period over which the climatology was performed was shifted to 2007 to allow access to radar algorithm information needed to classify a storm as a supercell. Archived radar imagery was used to classify systems as nonlinear convective events, isolated cells, clusters of cells, broken lines of cells, squall lines with no stratiform precipitation, trailing stratiform precipitation, parallel stratiform precipitation, and leading stratiform precipitation, and bow echoes. In addition, the three cellular classifications were subdivided to allow an analysis of severe weather reports for events in which supercells were present and those in which they were not. As in the earlier study, all morphologies were found to pose some risk of severe weather, and differences in the two datasets were generally small. The 2007 climatology confirmed the theory that supercellular systems produce severe weather more frequently than other morphologies, and also produce more intense severe weather. Supercell systems were especially prolific producers of tornadoes and hail relative to all other mor- phologies, but also produced severe wind and flooding much more often than nonsupercell cellular mor- phologies. These results suggest that it is important to differentiate between cellular morphologies containing rotation and those that do not when associating severe weather reports with convective morphology. 1. Introduction cipitation, whether the initial convection was linear or areal in coverage (or a combination), and whether sys- Many studies have attempted to classify mesoscale tems merged with others. Baldwin et al. (2005) used 1-h convective systems by organizational mode. Bluestein rainfall amounts to develop an automated classification and Jain (1985) classified squall lines in terms of their procedure that separated rainfall events into stratiform development as broken line, back building, broken areal, nonconvective, convective linear, and convective cellular and embedded areal. Parker and Johnson (2000) con- categories. Other studies used isolated cells as an orga- sidered squall lines with trailing stratiform precipitation, nizational mode (Grams et al. 2006), and Baldwin et al. parallel stratiform precipitation, and leading stratiform (2005) alluded to classifying systems as both isolated cells precipitation. Jirak et al. (2003) used satellite and radar and clusters of multicells. Gallus et al. (2008; hereafter data to separate mesoscale convective systems into four G08) used several of these morphologies and related categories: mesoscale convective complexes, persistent severe weather reports in the midwestern United States elongated convective systems, meso-b circular convec- to morphology type and added clusters of cells, squall tive systems, and meso-b elongated convective systems. lines with no stratiform precipitation, and nonlinear The same study also classified systems by development convective systems to the typology. on radar in terms of the presence of stratiform pre- No matter which classification system is used, classi- fication of convective system morphology can be diffi- Corresponding author address: Jeffrey D. Duda, 3134 Agronomy, cult. Some subjectivity is inherent in the classification Iowa State University, Ames, IA 50011. since some systems exhibit aspects of multiple mor- E-mail: [email protected] phologies (G08) with changes occurring both spatially DOI: 10.1175/2009WAF2222338.1 Ó 2010 American Meteorological Society FEBRUARY 2010 DUDA AND GALLUS 191 and temporally. For example, Parker and Johnson (2000), Detection Algorithm (MDA) (Stumpf et al. 1998) and Parker (2007), and Storm et al. (2007) noticed that squall the Tornado Detection Algorithm (TDA; Mitchell et al. lines with leading stratiform and parallel stratiform pre- 1998). Stumpf et al. (1998) showed the MDA to be a cipitation had a tendency to transform gradually to better identifier and predictor of supercells than the trailing stratiform precipitation squall lines. In addition, recent operational algorithm, the WSR-88D Build 9.0 the assignment of severe weather reports to particular Mesocyclone Algorithm, by comparing the probability morphologies also poses challenges (see G08 for a de- of detection and critical success index on a dataset. tailed discussion). Many of the difficulties are related to Mitchell et al. (1998) showed the TDA to be a better the methods used to report storms and how they appear identifier and predictor of tornadoes than the recent in the National Climatic Data Center’s (NCDC) Storm operational algorithm, the WSR-88D Tornadic Vortex Events Database. Such issues include the overreporting Signature Algorithm, by comparing the probability of or underreporting of severe wind and hail events (Trapp detection, false alarm rate, critical success index, and et al. 2006), the affects of population density on the re- Heidke skill score on a different dataset. The MDA may porting of severe wind events (Weiss et al. 2002), the be particularly useful for identifying supercells since methods by which tornadoes are reported (Doswell and a defining characteristic of a supercell is the presence