Storm Mode Variability over northern Alabama Within the Domain of the ARMOR Radar

Collectively known as part of Dixie Alley within the meteorological community, northern Alabama and southern middle Tennessee experience a broad spectrum of tornado producing thunderstorms. Since the Advanced Radar for Meteorological Research (ARMOR) became operational in April 2005, about 300 tornadogenesis events have been documented within the 120 km range of this radar. An analysis of the ARMOR data was undertaken to classify the parent storms associated with these tornadoes. The results show a nearly equal number of parent storms when classified into the broad categories of Mesoscale Convective Systems (MCS's) and supercell tornadoes. These broad categories were further decomposed into respective supercell genre consisting of high precipitation, hybrid, miniature, and classic, with high precipitation supercells dominating over half the categorical distribution. MCS events were further divided into separate genre consisting of Quasi-Linear Convective Systems (QLCS's), mesoscale vortices, embedded supercells, line segments, and bow echoes. To contribute to the understanding of tornado producing storm mode frequency with respect to number of tornado days, the total number of storm events was calculated pertaining to individual storm mode category. This feature provided valuable insight into how often the ARMOR domain experiences supercell and MCS tornado producing events holistically.

Also of interest to this investigation are research results regarding the synoptic and mesoscale meteorological parameters contributing to the tornadoes within this database. Consequently, Lifting Condensation Level (LCL) heights were recorded via archived surface data, and compared with measured ceilometer cloud base height data for tornadic storms occurring within 60 km of ARMOR. Other useful parameters including Mixed Layer CAPE (MLCAPE), 0-6 km bulk shear, and upper trough placement were assimilated in the study and correspondingly linked to storm mode category and respective genre. This set of parameters were also used to determine their dependence on the time of day (e.g., daytime vs nocturnal). This study provides insight into the occurrence of tornadoes in this region by linking calculated storm mode frequency to parameters that have been considered relevant to tornadogenesis.