Monday, 24 July 2017
Kona Coast Ballroom (Crowne Plaza San Diego)
Several case studies and numerical simulations have confirmed that baroclinic boundaries provide enhanced horizontal and vertical vorticity, wind shear, helicity, and moisture that induce stronger updrafts, higher reflectivity, and stronger low-level rotation in supercells. However, the distance at which a surface boundary will provide such enhancement is less well-defined. Previous studies have identified distances ranging from 5 km to 200 km and only focused on tornado production and intensity, rather than all forms of severe weather. To better aid short-term forecasts, the actual distances at which supercells produce severe weather in proximity to a boundary needs to be assessed.
In this study, the distance between a large number of supercells and nearby surface boundaries (including warm fronts, stationary fronts, and outflow boundaries) is measured throughout the lifetime of each storm; the distance at which associated reports of large hail, strong winds, and tornadoes occur is also collected. Statistical analyses assess the sensitivity of report distributions to report type, boundary type, and boundary strength. Additionally, the range at which each type of severe weather is produced for each boundary is identified to provide a useful operational tool for forecasters. Notably, tornadoes are more likely to be produced closer to a boundary than severe hail and wind. Overall, the observations point to a unique range at which severe weather occurs for each boundary and report type.
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