DISCRIMINATING BETWEEN TORNADIC AND NONTORNADIC THUNDERSTORMS USING MESOSCALE MODEL OUTPUT

The ability to discriminate between tornadic and nontornadic thunderst orms is investigated using a mesoscale model. Nine severe weather even ts are simulated: four events are tornadic supercell thunderstorm outb reaks that occur in conjunction with strong large-scale forcing for up ward motion, three events are bow-echo outbreaks that also occur in co njunction with strong large-scale forcing for upward motion, and two a re isolated tornadic supercell thunderstorms that occur under much wea ker large-scale forcing. Examination of the mesoscale model simulation s suggests that it is possible to discriminate between tornadic and no ntornadic thunderstorms by using the locations of model-produced conve ctive activity and values of convective available potential energy to highlight regions of likely thunderstorm development, and then using t he values of storm-relative environmental helicity (SREH) and bulk Ric hardson number shear (BRNSHR) to indicate whether or not tornadic supe rcell thunderstorms are likely. Values of SREH greater than 100 m(2) s (-2) indicate a likelihood that any storms that develop will have a mi dlevel mesocyclone, values of BRNSHR between 40 and 100 m(2) s(-2) sug gest that low-level mesocyclogenesis is likely, and values of BRNSHR l ess than 40 m(2) s(-2) suggest that the thunderstorms will be dominate d by outflow. By combining the storm characteristics suggested by thes e parameters, it is possible to use mesoscale model output to infer th e dominant mode of severe convection.