Contrast Between Good and Bad Forecasts of Warm Season MCS Rainfall

Abstract

Large variations in the accuracy of warm season MCS rainfall predictions are investigated by examining several wellforecasted and poorly forecasted cases from a sample of 20 events simulated using a 10 km grid spacing version of the Eta model. Two different convective schemes, the Betts–Miller–Janjic and Kain–Fritsch, have been used in the simulations to investigate in detail differences in simulated rainfall fields. The accuracy of the forecasts is evaluated using both subjective analysis and objective skill measures. The fact that subjective analysis does not necessarily agree with an objective analysis further argues for the development of new objective verification methods for quantitative precipitation forecasting. To gain some insight into possible causes of errors in the most poorly forecasted events, tests are performed where initialized relative humidity is adjusted to either encourage or discourage rainfall formation in specific regions.