## 3 Results
### Quantitative Analysis for Precipitation Forecast  
An evaluation of the model QPF was conducted using the scores of TS, BS, RMSE, PPMCC and SRCC, as defined in Section 2.4. The surface forecasts of the C1, C2 and C3 experiments were compared with the AWS observations. At the thresholds of 5, 10, 15, and 20 mm, the differences between the forecasts and observations for the 6-h accumulated precipitation were compared to examine forecast performance. Compared with group C1, groups C2 and C3 revealed substantial improvement in TS, with higher scores closer to one for the different thresholds of 6-h accumulated precipitation (Figure 14a). Among the C2 experiments, DA02 had the highest TS at the threshold of 5 mm but a lower TS at the thresholds of 10, 15, and 20 mm. DA03 had the highest TS at the threshold of 5 mm but a lower TS at the thresholds of 10, 15, and 20 mm. DA04 had a TS higher than or comparable to that of the other experiments for the thresholds of 5, 10, and 15 mm but a lower TS at thresholds of 20 mm. Among the C3 experiments for most of the thresholds, CDA01 had the lowest TS, and CDA02 and CDA03 had highest TS. Forecasting performance under different experiments was better if the BS was closer to one (Figure 14b). All C1 experiments with a BS < 1 provided an underestimated forecast for the different thresholds. C2 experiment DA04 and C3 experiment CDA04 also had a BS < 1 and featured an underestimated forecast. However, C2 experiments of DA01, DA02 and DA03 and C3 experiments of CDA02 and CDA03 generally had BS > 1 and produced an overestimated forecast. Similar to the TS (Figure 14a), at the thresholds of 15 and 20 mm, the BS had better scores close to one in the group C2 than in the group C1 (Figure 14b). Among the C2 experiments, DA04 had the highest skill of the BS at all thresholds, followed by DA02 and DA01 (Figure 14b). Among the C1 experiments, NDA03 and NDA04 had better skill of the BS at the thresholds of 5 and 10 mm (Figure 14b). Figure 13: Vertical cross section of maximum reflectivity and horizontal wind vector of CDA03 simulations at (**a**) 0600, (**b**) 0700, and (**c**) 0800 UTC (from 1400 to 1600 LST) on 5 August 2018, along the northwest-to-southeast plane (from x to x\({}^{\prime}\)) depicted in Figure 10. The title of each chart showed the accurate location of reflectivity we selected and the approximate location of Pingtung Air Force Base was depicted as black star. For the C1 and C2 group experiments, TS and BS tended to be higher at the thresholds of 5 and 10 mm than at 15 and 20 mm. Higher thresholds with lower scores might be due to the low forecast quality or lower number of observation stations for verification for the 6-h accumulated precipitation. For the thresholds of 5, 10, 15, and 20 mm, the station numbers  
Figure 14: (a)Threat Score (TS) and (b) Bias Score (BS) of C1, C2 and C3 experiments for the 6-h accumulated precipitation (mm) against the corresponding AWS observations during 0500–1100 UTC (1300–1900 LST). Verification thresholds are 5, 10, 15, and 20 mm. (percentage of station numbers for different thresholds relative to the total station numbers) were 70 (52%), 18 (13%), 12 (9%), and 8 (6%), respectively. A smaller RMSE indicates superior forecasting performance in the experiments. PPMCC and SRCC values closer to one also indicate better forecasting performance. The RMSE values (Figure 15a) revealed that the C2 experiment DA04 and C3 experiment CDA01 performed better than other experiments due to lower RMSE. In contrast, C2 experiments DA01 and DA03, and C3 experiment CDA02 had higher RMSE. The PPMCC values (Figure 15a) revealed that C2 performed better than C1 in all four experiments, with significant improvement in DA03 and DA04. Among all the experiments, CDA03 was the best-performing one. Among C2 experiments, DA04 was the best-performing, with an RMSE of 16.3 mm and a correlation coefficient of 0.3.