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Environmental and Observational Characteristics Associated with Tornadic QLCSs

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Monday, 5 November 2012
Symphony III and Foyer (Loews Vanderbilt Hotel)
Matthew E. Anderson, NOAA/NWSFO, Calera, AL; and K. B. Laws, B. M. Williams, and C. J. Rohrbach

Quasi-linear Convective Systems (QLCS) also known as bow echoes and Mesoscale Convection Systems (MCSs) are one of the convective modes known to produce an array of severe weather including damaging straight-line wind, large hail, and weak EF0 to strong EF3 tornadoes. Previous work found that 18% of the tornadoes across the U. S. from 1998-2000 were associated with QLCSs, and a maximum in QLCS tornado occurrence stretches from Alabama and Mississippi northward into the Ohio River Valley. A local study at the National Weather Service in Birmingham, AL found that 38% of all tornadoes across Central Alabama from 2007-2012 were attributed to QLCSs. Therefore, it is imperative that forecasters understand the environments and radar characteristics associated with QLCS tornadoes. The warning process is further exacerbated by the transient nature of the meso-vortices that develop along the leading edges of QLCSs. The same local study also indicated that overall statistical performance during QLCS events continues to lag behind that for supercells.

Environments favorable for QLCS tornado formation are usually associated with high values of shear in the lower atmosphere. However, the strength of low level shear alone cannot be used to determine the likelihood of tornadogensis within QLCSs. Studies have shown that tornadic meso-vortices associated with QLCSs tend to be more persistent, deeper, and tighter than their non-tornadic counterparts. Environmental and radar characteristics of QLCS events from 2007-2012 that occurred across the County Warning Area of the National Weather Service in Birmingham, AL were evaluated in this study. Although the study was limited to Central Alabama, the results should be applicable across the Southeastern U.S. This presentation will build upon others in developing a better understanding for the environmental conditions favorable for tornadic QLCS events compared to non-tornadic events as well as their radar characteristics. Additionally, weaker QLCSs that produced EF0 and EF1 tornadoes will be contrasted with those that produced the stronger EF2 and EF3 tornadoes. These results will lead to a better understanding of the mesoscale environment and radar characteristics, improving warning performance during QLCS events