The 21 January Huntsville tornado: Storm and mesoscale characteristics inferred from combined high-resolution dual-polarization radar data and video images

The 21 January tornado formed from a relatively shallow supercell storm that produced relatively few CG flashes. The mesocyclone and tornado formed on the upshear (western) flank within close range (10-20 km) of the ARMOR dual polarization radar. Because only weak precipitation (low concentration of large drops) developed within the upshear flanking line, the tornado and its antecedent wall cloud were clearly visible to thousands of people in the Huntsville area between 1700 and 1730 CST (rush hour). Consequently, a large number (>500) of high quality video images were taken data from many viewing locations around the tornado, from short range to long range. Such a diversity of video images offers an opportunity to document the visual appearance of the tornado and its parent supercell storm (mini supercell), and combine with high-resolution dual polarization radar data. This analysis focuses on the western storm flank containing the mesocyclone and tornado. Visual images indicate essentially no degradation in visibility around the tornado, even though ARMOR data show a thin hook echo (with large ZDR) in this region. Images showing the entire storm indicate that the mesocyclone and tornado formed within a relatively shallow flanking line feature in which the convective cloud top was about 6 km AGL. However, video animations indicate that this region of the storm was convectively vigorous. The video images also show an east-west line of shallow cumulus clouds close to the developing tornado; and perhaps indicate of a thermal boundary that played a role in tornadogenesis. These images are combined with available surface data to provide a meso-γ-scale analysis of the boundary layer immediately adjacent to the parent storm.