Prediction of Central Arizona Convection. Part I: Evaluation of the NGM and Eta Model Precipitation Forecasts

Abstract

The utility of numerical model guidance produced by the National Meteorological Center has been evaluated for the forecast of convection over central Arizona during the summer monsoon season. Model output from the Nested Grid Model (NGM) and Eta model has been compared to observations taken during the 1990 field experiment referred to as the Southwest Area Monsoon Project (SWAMP). The NGM precipitation forecasts showed little skill for events in which heavy precipitation was observed over Phoenix, Arizona. Selected events during the SWAMP period were simulated using the Eta model. Qualitative comparisons of the Eta model's precipitation forecasts with lightning data and satellite imagery suggest that the model has little skill over Arizona during the warm season. Nocturnal heavy precipitation over the lower deserts of central Arizona is nearly always preceded by afternoon convection over the mountains to the north and east. The convection over the mountains was absent in the model.