Forecasting the onset of Cloud-Ground Lightning Using Layered VerticallyIntegrated Liquid Water

Accurate forecasting of cloud-ground (CG) lightning onset at the Kennedy Space Center (KSC), Florida is critical for personnel safety, but presents a difficult problem. Current methods for predicting CG lightning onset rely on radar analyses that require a reflectivity threshold to be exceeded at a specified temperature level. Although the requisite temperature level used in lightning forecasting lies within the critical region of convection for lightning initiation (-10 to -20 degrees C), current methods of prediction do not employ a complete description of the storm structure. This thesis hypothesizes that diagnosing the storm structure within the -10 to -20 degrees C layer is a key element in forecasting lightning onset. This storm structure can readily be described by the variation of the liquid water content, termed layered vertically integrated liquid (LVIL), within two layers in the supercooled region (-10 to -15 degrees C and -15 to -20 degrees C). An LVIL value for each layer, described together as a threshold pair, quantifies the minimum vertical structure required for lightning onset. The optimal threshold pair follows from weighting measures of forecast skill; in order of importance, they are probability of detection (POD), Kuipers skill score (KSS) and false alarm rate (FAR). LVIL amounts of 0.5 mm in the -10 to -15 degrees C layer coinciding with amounts of 0.25 mm in the -15 to -20 degrees C layer indicate that lightning is imminent, with a POD of 96%, a KSS of 51% and a FAR of 21%. This two-layer approach is superior to one-parameter methods currently in use at the KSC.Air Force Inst of Tech Wright-Patterson AFB OH is the author of 'Forecasting the onset of Cloud-Ground Lightning Using Layered VerticallyIntegrated Liquid Water', published 2000 under ISBN 9781423551737 and ISBN 1423551737.