Environments Associated with Slow-Moving Supercells: Tornadic and Nontornadic

Slow-moving supercells, defined by storm motion of ≤ 9 knots (4.5 ms^-1), provide operational and communication challenges for forecasters, the media, and emergency managers, especially when slow storm motions occur unexpectedly or are not well forecasted. Additionally, these slow-moving supercells also frequently produce long periods of heavy rain, causing flash flooding, which can carry high socioeconomic impacts. This study produces a climatology of slow-moving supercells and their respective synoptic and mesoscale environments over a 5-year period from 2009-2013 across the central contiguous United States. Aside from the traditional analysis of the instability and wind profile of the atmosphere, potential mesoscale contributions to slow storm motions, such as surface boundaries in the near-storm environment, are also analyzed to determine how boundary interactions contribute to slow storm motions. Further, in order to differentiate the environmental conditions encountered by slow-moving tornadic and nontornadic supercells, a comparison is drawn to identify which forecast parameters provide skill in discriminating situations where slow-moving supercells may be more likely to produce tornadoes.