Evaluating Severe Convective Wind Environments and Radar Signatures

The National Weather Service (NWS) has defined a severe thunderstorm as one with large hail (≥1” in diameter) and strong winds (≥50 kt wind gust). Due to recent improvements to the WSR-88D network, large hail has become easier to identify in radar data, while recognizing damaging winds remains a challenge. A downburst is a strong downdraft that causes an outflow of damaging winds at or near the surface. When downburst winds strike the surface, they spread out horizontally very quickly and can pose a threat to aviation and property. Forecasting for downburst events proves challenging even for veteran forecasters. The dual polarization upgrade to the WSR-88D network provides forecasters with additional information to better evaluate storms with downburst potential. This research seeks to isolate any trends or patterns in environmental parameters and radar signatures leading up to downburst events, with the specific goal of assisting NWS forecasters in improving precision, confidence, and lead time when making downburst warning decisions. This study evaluated 19 downburst events throughout northern Ohio and northwest Pennsylvania between 2012 and 2017. BUFKIT was used to analyze numerical weather model environmental parameters believed to indicate a prime environment for downbursts. Additionally, GR2Analyist was used to interrogate radar data, specifically changes to Base Reflectivity (Z), Differential Reflectivity (Z_DR), and Specific Differential Phase (K_DP) in the time leading up to downburst initiation. A set of guidelines were developed to increase the situational awareness and confidence of NWS Cleveland, Ohio forecasters when making downburst warning decisions.