A Lightning Activity Forecast Scheme Developed for Summer Thunderstorms in South China

Based on the relationship between lightning flash density and radar echoes and a statistical analysis using satellite and radar observations, a scheme was introduced into the mesoscale model GRAPES (Global and Regional Assimilation and PrEdiction System) to forecast the cloud to ground (CG) flash activities. Because the relationship is a necessary but not sufficient condition for lightning, an additional constraint condition related to temperature of cloud top is added into the scheme to determine whether the lightning activity really occurs. Only if the lightning activity meets the criterion to occur, the CG flash density in a grid is considered to be valid. This was proved to be necessary for reducing the false prediction. Two cases that occurred on the edge of the subtropical high in coastal regions of South China were simulated to examine the efficiency of the scheme. The results showed that the scheme was capable of forecasting lightning activities in South China. The simulated lightning areas agreed with the CG flash observations, and the CG flash density forecast by the model was also consistent with observational results in magnitude. In consideration of the forecast aging of the explicit cloud microphysical scheme in GRAPES, lightning activities can now be forecast accurately within 6 h.