## Author Contributions

Conceptualization, H.Z. and X.M.; data curation, X.M. and A.A.; formal analysis, H.Z. and H.L.; funding acquisition, H.L.; investigation, H.Z., X.M. and A.A.; methodology, H.Z., J.L. and H.L.; resources, J.L., H.L. and A.A.; software, H.Z., J.L. and A.A.; supervision, X.M. and H.L.; validation, H.Z., J.L. and A.A.; visualization, J.L.; writing—original draft, H.Z.; writing—review & editing, H.Z. All authors have read and agreed to the published version of the manuscript.

**Figure 1.**
The two nested domains with horizontal grid spacings of 9 and 3 km for Weather Research and Forecasting (WRF) simulation. The inner simulation domain covers Xinjiang completely.

**Figure 1.**
The two nested domains with horizontal grid spacings of 9 and 3 km for Weather Research and Forecasting (WRF) simulation. The inner simulation domain covers Xinjiang completely.

**Figure 2.**
The soil moisture contents of 10–cm topsoil layer of the Noah land surface model (LSM) of six WRF simulations: (**a**) 1.0 multiple of National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) soil moisture; (**b**) 1.25 multiples of NCEP GFS soil moisture; (**c**) 1.5 multiples of NCEP GFS soil moisture; (**d**) 2.0 multiples of NCEP GFS soil moisture; (**e**) 2.5 multiples of NCEP GFS soil moisture; and (**f**) 3.0 multiples of NCEP GFS soil moisture.

**Figure 2.**
The soil moisture contents of 10–cm topsoil layer of the Noah land surface model (LSM) of six WRF simulations: (**a**) 1.0 multiple of National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) soil moisture; (**b**) 1.25 multiples of NCEP GFS soil moisture; (**c**) 1.5 multiples of NCEP GFS soil moisture; (**d**) 2.0 multiples of NCEP GFS soil moisture; (**e**) 2.5 multiples of NCEP GFS soil moisture; and (**f**) 3.0 multiples of NCEP GFS soil moisture.

**Figure 3.**
The water vapor evolution of the single-column model (SCM) simulations under different initial conditions of soil moisture content: (**a**) soil moisture = 0.1; (**b**) soil moisture = 0.2; (**c**) soil moisture = 0.4; and (**d**) soil moisture = 0.6. The potential temperature evolution of the SCM simulations under different initial conditions of soil moisture content: (**e**) soil moisture = 0.1; (**f**) soil moisture = 0.2; (**g**) soil moisture = 0.4; and (**h**) soil moisture = 0.6. All simulations are at Urumqi (43.79° N, 87.65° E). The x-axis represents the hours since the simulation, while the y-axis shows the model vertical coordinate (the small value represents high altitude).

**Figure 3.**
The water vapor evolution of the single-column model (SCM) simulations under different initial conditions of soil moisture content: (**a**) soil moisture = 0.1; (**b**) soil moisture = 0.2; (**c**) soil moisture = 0.4; and (**d**) soil moisture = 0.6. The potential temperature evolution of the SCM simulations under different initial conditions of soil moisture content: (**e**) soil moisture = 0.1; (**f**) soil moisture = 0.2; (**g**) soil moisture = 0.4; and (**h**) soil moisture = 0.6. All simulations are at Urumqi (43.79° N, 87.65° E). The x-axis represents the hours since the simulation, while the y-axis shows the model vertical coordinate (the small value represents high altitude).

**Figure 4.**
The (**a**) sensible heat fluxes (SHFs); (**b**) latent heat fluxes (LHFs); (**c**) LHFs + SHFs and (**d**) upward moisture fluxes at the ground surface (QFXs) of the SCM simulations under different soil moisture initial conditions. The black line represents the soil moisture equal to 0.1; the green line represents the soil moisture equal to 0.2; the blue line represents the soil moisture equal to 0.4; and the red line represents the soil moisture equal to 0.6. The x-axis represents the number of hours since the simulation.

**Figure 4.**
The (**a**) sensible heat fluxes (SHFs); (**b**) latent heat fluxes (LHFs); (**c**) LHFs + SHFs and (**d**) upward moisture fluxes at the ground surface (QFXs) of the SCM simulations under different soil moisture initial conditions. The black line represents the soil moisture equal to 0.1; the green line represents the soil moisture equal to 0.2; the blue line represents the soil moisture equal to 0.4; and the red line represents the soil moisture equal to 0.6. The x-axis represents the number of hours since the simulation.

**Figure 5.**
The (**a**) downward long-wave radiation fluxes (GLW); (**b**) downward short-wave radiation (SWDOWN); (**c**) upward short-wave radiation (UPSW) and (**d**) upward long-wave radiation (UPLW) of the SCM simulations under different soil moisture initial conditions. The black line represents the soil moisture equal to 0.1; the green line represents the soil moisture equal to 0.2; the blue line represents the soil moisture equal to 0.4; and the red line represents the soil moisture equal to 0.6. The x-axis represents the number of hours since the simulation.

**Figure 5.**
The (**a**) downward long-wave radiation fluxes (GLW); (**b**) downward short-wave radiation (SWDOWN); (**c**) upward short-wave radiation (UPSW) and (**d**) upward long-wave radiation (UPLW) of the SCM simulations under different soil moisture initial conditions. The black line represents the soil moisture equal to 0.1; the green line represents the soil moisture equal to 0.2; the blue line represents the soil moisture equal to 0.4; and the red line represents the soil moisture equal to 0.6. The x-axis represents the number of hours since the simulation.

**Figure 6.**
The specific humidity of 700-hPa at 002 UTC 17 August 2019 of the WRF simulations under different soil moisture initial conditions. (**a**) 1.0; (**b**) 1.25; (**c**) 1.5; (**d**) 2.0; (**e**) 2.5; and (**f**) 3.0 multiples of NCEP GFS soil moisture represent (**a**) “1.0 soil moisture”; (**b**) “1.25 soil moisture”; (**c**) “1.5 soil moisture”; (**d**) “2.0 soil moisture”; (**e**) “2.5 soil moisture”; and (**f**) “3.0 soil moisture”, respectively.

**Figure 6.**
The specific humidity of 700-hPa at 002 UTC 17 August 2019 of the WRF simulations under different soil moisture initial conditions. (**a**) 1.0; (**b**) 1.25; (**c**) 1.5; (**d**) 2.0; (**e**) 2.5; and (**f**) 3.0 multiples of NCEP GFS soil moisture represent (**a**) “1.0 soil moisture”; (**b**) “1.25 soil moisture”; (**c**) “1.5 soil moisture”; (**d**) “2.0 soil moisture”; (**e**) “2.5 soil moisture”; and (**f**) “3.0 soil moisture”, respectively.

**Figure 7.**
(**a**) Specific humidity; (**b**) potential temperature; (**c**) geopotential height (GPH) and (**d**) wind speed BIAS verified against observations of 14 meteorological sounding stations in Xinjiang under different soil moisture initial conditions. Note that the 1.0, 1.25, 1.5, 2.0, 2.5 and 3.0 multiples of NCEP GFS soil moisture are denoted as black, green, blue, red, brown and yellow lines, respectively. The figure shows the verification results for the upper air forecasts. The x-axis represents the BIAS, while the y-axis represents the values of different isobaric surfaces.

**Figure 7.**
(**a**) Specific humidity; (**b**) potential temperature; (**c**) geopotential height (GPH) and (**d**) wind speed BIAS verified against observations of 14 meteorological sounding stations in Xinjiang under different soil moisture initial conditions. Note that the 1.0, 1.25, 1.5, 2.0, 2.5 and 3.0 multiples of NCEP GFS soil moisture are denoted as black, green, blue, red, brown and yellow lines, respectively. The figure shows the verification results for the upper air forecasts. The x-axis represents the BIAS, while the y-axis represents the values of different isobaric surfaces.

**Figure 8.**
The (**a**) 2-m specific humidity BIAS; (**b**) 2-m specific humidity RMSE; (**c**) 2-m temperature BIAS and (**d**) 2-m temperature RMSE verified against observations of 105 meteorological stations in Xinjiang under different soil moisture initial conditions. Note that the 1.0, 1.25, 1.5, 2.0, 2.5 and 3.0 multiples of NCEP GFS soil moisture are denoted as black, red, orange, green, blue and yellow lines, respectively. The figure shows the verification results of the surface forecasts. The x-axis represents the hours since the simulation, while the y-axis represents the BIAS or RMSE.

**Figure 8.**
The (**a**) 2-m specific humidity BIAS; (**b**) 2-m specific humidity RMSE; (**c**) 2-m temperature BIAS and (**d**) 2-m temperature RMSE verified against observations of 105 meteorological stations in Xinjiang under different soil moisture initial conditions. Note that the 1.0, 1.25, 1.5, 2.0, 2.5 and 3.0 multiples of NCEP GFS soil moisture are denoted as black, red, orange, green, blue and yellow lines, respectively. The figure shows the verification results of the surface forecasts. The x-axis represents the hours since the simulation, while the y-axis represents the BIAS or RMSE.

**Figure 9.**
The 24-h accumulative precipitation at 002 UTC 17 August 2019 of the WRF simulations under different soil moisture initial conditions. Note that (**a**) 1.0; (b) 1.25; (**c**) 1.5; (**d**) 2.0; (**e**) 2.5; and (**f**) 3.0 multiples of NCEP GFS soil moisture are denoted as (**a**) “1.0 soil moisture”; (**b**) “1.25 soil moisture”; (**c**) “1.5 soil moisture”; (**d**) “2.0 soil moisture”; (**e**) “2.5 soil moisture”; and (**f**) “3.0 soil moisture”, respectively. Precipitation is measured in millimeters.

**Figure 9.**
The 24-h accumulative precipitation at 002 UTC 17 August 2019 of the WRF simulations under different soil moisture initial conditions. Note that (**a**) 1.0; (b) 1.25; (**c**) 1.5; (**d**) 2.0; (**e**) 2.5; and (**f**) 3.0 multiples of NCEP GFS soil moisture are denoted as (**a**) “1.0 soil moisture”; (**b**) “1.25 soil moisture”; (**c**) “1.5 soil moisture”; (**d**) “2.0 soil moisture”; (**e**) “2.5 soil moisture”; and (**f**) “3.0 soil moisture”, respectively. Precipitation is measured in millimeters.

**Figure 10.**
The critical success index (CSI) and frequency bias (FBIAS) values of 24-h accumulative precipitation of the WRF simulations under different soil moisture initial conditions at each precipitation magnitude: (**a**,**g**) 0.1 mm; (**b**,**h**) 3.1 mm; (**c**,**i**) 6.1 mm; (**d**,**j**) 12.1 mm; (**e**,**k**) 24.1 mm; and (**f**,**l**) 48.1 mm. The 1.0, 1.25, 1.5, 2.0, 2.5 and 3.0 multiples of NCEP GFS soil moisture are represented as black, red, orange, green, blue and yellow columns, respectively.

**Figure 10.**
The critical success index (CSI) and frequency bias (FBIAS) values of 24-h accumulative precipitation of the WRF simulations under different soil moisture initial conditions at each precipitation magnitude: (**a**,**g**) 0.1 mm; (**b**,**h**) 3.1 mm; (**c**,**i**) 6.1 mm; (**d**,**j**) 12.1 mm; (**e**,**k**) 24.1 mm; and (**f**,**l**) 48.1 mm. The 1.0, 1.25, 1.5, 2.0, 2.5 and 3.0 multiples of NCEP GFS soil moisture are represented as black, red, orange, green, blue and yellow columns, respectively.

**Table 1.**
Initial conditions of the single-column model (SCM) ideal experiment.

**Table 1.**
Initial conditions of the single-column model (SCM) ideal experiment.

Vertical Level | Model Top (km) | Soil Moisture (%) | U (m/s) | V (m/s) | Potential Temperature (K) | Specific Humidity (k/kg) | Coordinates (°) | Start Time (UTC) |
---|

60 | 6 | 0.1 0.2 0.4 0.6 | 10 | −7 | 301(surface)–328(top) | 0 | 43.78° N 87.65° E | 2019081500 |