Damaging winds produced by cold-season quasi-linear convective systems in the southeast US: preliminary findings and planned research

Quasi-Linear Convective Systems (QLCS's) are a very common meteorological phenomenon in the southeastern United States. This term covers squall lines, bow echoes, line-echo wave patterns (LEWP's) and other mesoscale convective systems with a linear precipitation structure. With regards to bow echoes, Johns (1993) states that the “dynamic” pattern of bow echo development reaches a maximum in the southeast U.S. in the winter months. Normally, these systems occur in advance of a cold front with an extensive squall line and embedded LEWP's. Ashley & Mote (2005) indicated that 20.9 derecho events occur each year over the entire United States, accounting for $95.7 M in damage (per event), as well as 8.5 fatalities and 144.7 injuries annually. This study only covered convective wind events classified as derechoes; it did not take into account smaller-scale events that can still cause massive damage and loss of life.

QLCS's in the southeast are not a well-researched topic. There have been large field campaigns such as PRE-STORM (1985) and BAMEX (2003), but these have mainly focused on warm-season systems in the Great Plains and upper Midwest. Only a few studies have been solely focused on cold-season QLCS's (Elkins and Knupp 2010). The focus of this research is to determine the typical mode of cold-season QLCS's in the southeast by understanding their general structure, typical features and verifying their governing dynamics. It is hypothesized that cold-season frontal QLCS's in the southeast exhibit mainly slabular convection (i.e., the value of slabularity is close to unity), owing to generally low CAPE, stable low levels, and high values of low-level wind shear. The cold pool is fairly homogenous along the line, while the precipitation structure is very linear near the surface.

This question and hypothesis will be examined through radar analysis of numerous case studies. Thus far, 28 cases have been identified from November 2000 to October 2009. Priority is given to the cases exhibiting the highest damage estimates. The majority of the analysis will be within a single-Doppler vertical plane normal to the QLCS major axis, for cases that exhibit a 2-D structure. This condition facilitates a relatively accurate calculation of 2-D airflow and insight into the dynamic processes of the systems.

In addition to the archived cases, a field study will be conducted over the next two cold seasons (2010-11, 2011-12) in which the UAH MAX (Mobile Alabama X-Band radar) and MIPS (Mobile Integrated Profiling System, including a 915 MHz profiler, X-band profiling radar, lidar celiometer, microwave profiling radiometer and a balloon sounding system) will be deployed in conjunction with other surface-based radars to achieve multi-Doppler analyses of cold-season QLCS's. The main network will be centered on Huntsville (using KHTX WSR-88D and UAH ARMOR,) while secondary networks will be located in Columbus, MS (KGWX) and Memphis (KNQA and a TDWR.)