## 2 Field Experiment and WRF Model Setup  
### Field Measurement and Instrumentation  
This field experiment was conducted over the northern slope of the middle Tian Shan area on 27 July 2019. As shown in Figure 1, a vertical pointing radiometer, located at Mushi site, was used to measure the ambient conditions such as the temperature and humidity. The precipitation rate was measured by rain gauges (Figure 1b) operated by the China Metrological Administration. Two ground-based radars, including a Ka-band cloud radar on a truck and a micro-rain radar (MRR), were deployed to measure the cloud and precipitation structure. The MRR, which has a wavelength of 12.38 mm (24 GHz), is able to measure the vertical structure of precipitation. It may respond to clouds as well if there are large particles, such as in convective clouds, but it struggles to detect cloud tops. Ka-band cloud radar is more sensitive to clouds compared to MRR because of its shorter wavelength (8.59 mm); thus, it can be used to measure the characteristics of non-precipitating clouds and for estimating the cloud tops. By combining MRR and cloud radar, the fine structure and evolution of clouds and the precipitation system could be investigated. The radiometer had 22 channels, which were used to measure the intensity of the radiation emitted by the atmosphere from a near-surface level to a 10 km height. It included two radio frequency subsystems in the same cabinet that shared the same antenna and antenna pointing system. The temperature profiling subsystem utilized sky observations at selected frequencies between 51.25 GHz and 58 GHz. The water vapor profiling subsystem received at selected frequencies between 22.235 GHz and 28 GHz. Temperature profiles could be obtained by measuring the radiation intensity or brightness temperature using the 14 channels along the side of the oxygen feature at 60 GHz. By scanning downward from line center, where the opacity is so great that all signal originates from just above the antenna, onto the wing of the line, where the radiometer \"sees\" deeper into the atmosphere, the instrument could obtain altitude information. Emissions at any altitude are proportional to the local temperature and density of oxygen; thus, the temperature profile could be retrieved. Water vapor profiles could be obtained by observing the intensity and shape of emissions from pressure-broadened water vapor lines. The eight channels in the water vapor absorption band were used for the retrieval. The emissions from water vapor were in a narrow line at high altitudes and were pressure-broadened at low altitudes. The  
Figure 1: (**a**) Domains of the WRF model simulation and topography. D01, D02, and D03 indicate the three nested domains used in the simulation; (**b**) Topography of the middle of the Tian Shan area. The red triangle indicates the location of Ka-band radar, the red vertical line in (**b**) indicates the range of the range–height indicator (RHI) scan, the blue dot indicates the location of an MRR, and the black dots in (**b**) indicate the locations of rain gauges. intensity of the emissions was proportional to the vapor density and temperature. Scanning the spectral profile and mathematically inverting the observed data could therefore provide water vapor profiles. The liquid water path (LWP) was obtained by measuring the contribution of vertically integrated liquid water to atmospheric spectral features of varying opacity. Liquid water information in both the oxygen and water vapor absorption bands was utilized by the radiometer. To calculate the relative contribution from liquid water, the temporally closest clear-sky opacity was used as a reference in the retrieval. The MRR, pointing vertically with 30 range gates and a range resolution of 100 m, was located at the Mushi site (Figure 1b) and used to measure the precipitation system. The core component of the radar was a frequency-modulated Gunn diode oscillator with an integrated mixing diode.