Nowcasting of 1-h precipitation using radar and NWP data

A multiple linear regression model complemented by a correction procedure (REG) is applied to nowcasting of 1-h precipitation for warm seasons. The model aims at predicting the mean area precipitation in the 9 km × 9 km squares for the territory of the Czech Republic. Precipitation amounts are calculated from the radar reflectivity measured by two C band radars, which are operated by the Czech Hydrometeorological Institute. The model predictors are obtained from: (i) radar-derived precipitation in the squares; (ii) radar-derived precipitation advected by wind fields at the 700 hPa level produced by ALADIN/LACE NWP model forecast; (iii) variables derived from forecasts of the ALADIN/LACE NWP model. Accuracy of the REG forecast is evaluated and compared with the forecast obtained by the advection of precipitation fields by the NWP wind at the 700 hPa level (ADV). The ADV forecast serves as one of the predictors (ii). Results show that REG yields apparently better forecasts than ADV in terms of RMSE, correlation coefficients and categorical measures. Also local precipitation maxima have better positions with respect to the real ones. However, if ADV did not indicate any precipitation, REG was not capable to forecast a convective precipitation development. This fact deteriorates the REG accuracy during afternoon hours. We may say that the REG forecast is more accurate in night and morning hours since the situation mentioned occurs quite scarcely during those time periods.