A Brief Overview of the History of Convective Lines and Bow Echoes from the 1950s to Now. A Review of the Advancement of Research of Convective Systems and Transfer of Knowledge to Operational Meteorology

Organized convective lines (quasi-linear convective systems, or QLCSs), and bow echoes represent one of the most unique challenges to warning operations at the National Weather Service (NWS). These convective complexes may be responsible for the production of long swaths of damaging surface winds, tornadoes of varying intensities, and a mixed mode of supercells and bowing segments within the larger convective line. This study will summarize the early studies of convective lines to the current research and warning practices applied today at Weather Forecast Offices (WFOs). One of the first studies relating accelerations and decelerations within a convective line to severe straight line winds and tornadoes was conducted by Nolen (1959) who coined the term “LEWP,” a line echo wave pattern (LEWP). Other researchers following him also associated severe straight line winds and tornadoes occurring with LEWPs (e.g., Cook 1961; Hamilton 1970). However, it was not until 1978 that the term “bow echo” was first established. The NIMROD project was led by T. Theodore Fujita, during which he developed the classic Bow Echo model, providing a conceptual model basis for the operational community. Other early critical studies furthered this operationally-based bow echo research, including Fujita's study of intense wet and dry microbursts, as well as Wakimoto's and Forbes' case study of leading-edge tornadoes and downbursts. In the late 1970s and early 1980s, research on the characterization of bow echo patterns was beginning to surface. Johns and Hirt investigated numerous long-tracked wind storms (“derechos”) across the central and eastern United States, and categorized these radar echo structures into two categories, progressive and serial (1987). Przybylinski, and DeCaire's (1985) investigations of reflectivity patterns of bow echo cases led to the development of four reflectivity conceptual models of mature bow echo systems. Concurrently, the “Pre-Storm Project” (1985) investigated reflectivity and velocity structures of mature mesoscale convective systems (MCSs). Houze and Smull (1987) and other collaborators made further strides in this research, namely the discovery of two dominate mesoscale airflow structures, front-to-rear (F-T-R) flow and the rear inflow jet (RIJ). Additional observational insights on bow echo evolution continued into the early 1990s (Smull and Burgess (1990); Moller, Doswell and Przybylinski (1990)). With the growing interest in long-lived convective lines, numerical modeling was introduced to the operational community around the same time. Early theory work started in the late 1980s by Rutunno and Wesiman; however, it was not until early 1990s where Weisman introduced this to the operational community. New insights were gained by these simulations, including the four stages of an idealized bow echo, the origins and role of book-end vortices, and a newly named feature, the “mesovortex” (Weisman and Davis 1998). The next significant advancement in bow echo research came with the installation of the WSR-88D network during the 1990s over the United States, furthering observational research. Many of these studies focused on storm-scale mesovortices (less than 10 km in diameter) to book-end vortices (10 to 30 km in diameter). Many bow echo and mesovortex studies were completed in the 1990s (e.g., Atkins and Przybylinski; Funk; McAvoy; Pence; Przybylinski and Schmocker; and Trayers and Riordan). Importantly, Przybylinski published an article summarizing the various radar reflectivity patterns of bow echoes and larger convective lines (1995). Parker and Johnson (2000) conducted an extensive study of MCSs, classifying them into three modes: trailing stratiform (TS), leading stratiform (LS) and parallel stratiform (PS). Another increase in bow echo research came with The Bow Echo and MCV Experiment (BAMEX), conducted during the summer of 2003 over the Midwest. This field study led to new observational insights on the environment and kinematic structure of MCSs and meso-convective vorticies (MCVs). Several damaging wind cases were collected, though one case in particular revealed that tornadoes and damaging downbursts occurred during the early part of the bowing stage, while the bow echo system evolved into a damaging wind event thereafter. The second component of the BAMEX project included the study of MCVs from both ground and aircraft observations. Trier, Davis, Galameau Jr. and Bosart led this component of the study, where numerous publications resulted during the 2000s (e.g., Wheatley, Trapp, and Atkins; Atkins et al.; Wakimoto et al.; Trier and Davis; and Galameau Jr. and Bosart). After the BAMEX project, a limited number of numerical simulation studies on bow echoes and mesovortex evolution were completed (e.g., Atkins and St. Laurent Parts 1 and 2; Weisman et al.), with observational convective line case studies continuing through 2010 from numerous WFOs (e.g., Izzi et al.; Sieveking and Przybylinski). All of the aforementioned numerical and observational research has led us to the present. There are a few theories on conceptual models of bow echoes, and continued observational studies and discoveries with the advancements in radar technology. This presentation will summarize the early studies of convective lines to the current research and warning practices applied today at NWS Offices (WFOs). Thereafter, the authors will discuss where the community needs to go from here in order to solidify conceptual models of the bow echo, and how best to apply these in warning operations.